MPLAB C Compiler for PIC32 v2.01, Release Notes

# Release Notes for MPLAB® C Compiler for PIC32 MCUs

## v2.01
August 2011

# Table of Contents

1. Overview
2. GNU General Public License
3. Devices Supported
4. Installation
5. Compiler Documentation
6. What's New
7. Migration Issues
8. Documentation Updates
9. Fixed Issues
10. Known Issues
11. Editions and License Upgrades
12. Customer Support

1. # Overview

   The 32-Bit language tools consist of a compiler (pic32-gcc), an assembler (pic32-as), a linker (pic32-ld), and an archiver/ librarian (pic32-ar). Additional tools distributed with this release include a binary to Intel[intl] Hex converter (pic32-bin2hex) and miscellaneous binary utilities (pic32-strip, pic32-strings, pic32-readelf, etc). In addition, the compiler utilizes a license manager (pic32-lm) as part of the time-limited MPLAB C Compiler for PIC32 MCUs Standard Evaluation edition.

   As described in the user's guides, all of the language tools are sensitive to case on the command line, including the case of file names. In particular, the C compiler shell (pic32-gcc) requires that C source files be named on the command-line with a lower-case .c extension. If an upper-case .C filename extension is used, the compiler assumes that the file is a C++ file, which is not supported. Similarly, the compiler shell passes a file with an upper-case .S filename extension through the C preprocessor before passing it to the assembler, but it passes a file with a lower-case .s extension directly to the assembler.

2. # GNU General Public License

   The MPLAB® C Compiler for PIC32 MCUs tools are written and distributed under the GNU General Public License (GPL) which means that its source code is freely distributed and available to the public.

   The source for the tools under the GNU GPL may be downloaded separately from the Microchip WWW web page. You may read the GNU GPL in the file named COPYING3.GPL located the docs subdirectory of your install directory. A general discussion of principles underlying the GPL may be found at www.gnu.org/copyleft.

   Support code provided for the header files, linker scripts, and runtime libraries are proprietary code and not covered under the GPL. See the full MPLAB C Compiler for PIC32 MCUs License Agreement for details.

3. # Devices Supported

   The following PIC32MX devices are supported:

   Part Number | Part Number | Part Number | Part Number
   --- | --- | --- | ---

   PIC32MX110F016B
   PIC32MX110F016C
   PIC32MX110F016D
   PIC32MX120F032B
   PIC32MX120F032C
   PIC32MX120F032D
   PIC32MX210F016B
   PIC32MX210F016C
   PIC32MX210F016D
   PIC32MX220F032B
   PIC32MX220F032C
   PIC32MX220F032D

   PIC32MX320F032H
   PIC32MX320F064H
   PIC32MX320F128H
   PIC32MX320F128L
   PIC32MX340F128H
   PIC32MX340F128L
   PIC32MX340F256H
   PIC32MX340F512H
   PIC32MX360F256L
   PIC32MX360F512L
   PIC32MX420F032H
   PIC32MX440F128H
   PIC32MX440F128L
   PIC32MX440F256H
   PIC32MX440F512H
   PIC32MX460F256L
   PIC32MX460F512L

   PIC32MX534F064H
   PIC32MX534F064L
   PIC32MX564F064H
   PIC32MX564F064L
   PIC32MX564F128H
   PIC32MX564F128L
   PIC32MX575F256H
   PIC32MX575F256L
   PIC32MX575F512H
   PIC32MX575F512L
   PIC32MX664F064H
   PIC32MX664F064L
   PIC32MX664F128H
   PIC32MX664F128L
   PIC32MX675F256H
   PIC32MX675F256L
   PIC32MX675F512H
   PIC32MX675F512L
   PIC32MX695F512H
   PIC32MX695F512L

   PIC32MX764F128H
   PIC32MX764F128L
   PIC32MX775F256H
   PIC32MX775F256L
   PIC32MX775F512H
   PIC32MX775F512L
   PIC32MX795F512H
   PIC32MX795F512L

   The PIC32MXGENERIC device is, as its name implies, a non-specific target that can be used to represent a generic core device.

4. # Installation on Windows

   If using MPLAB IDE, be sure to install MPLAB IDE v8.10 (or later) or MPLAB X beta 7 (or later) before installing these tools.

   To install the MPLAB C Compiler for PIC32 MCUs tools, perform the following steps:

   1. Locate the setup program on the 'MPLAB C Compiler for PIC32 MCUs' CD ROM.
   2. Run the setup program.
   3. Follow the directions on the screen. To install the standard evaluation edition, leave the license-key field blank when prompted. To install the full standard edition, enter your full license key.
   4. If the installation program indicates that it is necessary, reboot your computer to complete the installation.
   5. When the installation is complete, verify that the executable directory has been correctly added to your PATH (i.e., if you chose to install the tools in the default directory, c:\Program Files\Microchip\mplabc32\<version>, then ensure that c:\Program Files\Microchip\mplabc32\<version>\bin has been added to your PATH.

      From a Windows command prompt (cmd.exe), type: c:\>PATH

   To upgrade to a full standard-edition license from a lite or standard -evaluation edition license, follow the steps described in this section.

5. # Compiler Documentation

   The following documents pertain to the MPLAB C Compiler for PIC32 MCUs. They may be installed in the compiler's doc subdirectory, but you should check Microchip's website for the latest revisions.

   - MPLAB® C Compiler for PIC32 MCUs User's Guide (DS51686)
   - MPLAB® 32-Bit Language Tools Libraries (DS51685)
   - Microchip PIC32MX Peripheral Library - Compiled Help (CHM)1
   - MPLAB® MPLAB Assembler, Linker and Utilities for PIC32 MCUs User’s Guide (DS51833)

   1 Other CHM files may be available from the main CHM file by clicking a link (such as for Interrupts). When you do this, a Security Warning dialog may display. Click on Open to view the CHM file.

   Additional documentation on the GNU Assembler and Linker is available on the GNU Binutils v2.20 website.

6. # What's New

   ## New Features in v2.01

   - New device support -- This release introduces support for several new PIC32MX1 and MX2 devices.

   - unsupported(message) attribute -- Use the unsupported(message) attribute to emit a message whenever an unsupported function or variable is used.

     `__attribute__((unsupported("this feature is not supported on this device"))) void function(void);`

   ## New Features in v2.00

   - Upgrade to GCC 4.5.1 technology -- The MPLAB C compiler is now based on the GNU Compiler Collection (GCC) v4.5.1. This new base technology introduces a new optimization framework that allows for significantly improved generated code efficiency, resulting in both an improved code-size footprint and a faster execution speed.

   - Upgrade to Binutils 2.20 -- The MPLAB ASM32 assembler, LINK32 linker, and binary utilities are now based on GNU Binutils 2.20.

   - `address`(addr) C Attribute for functions and variables -- The `address` attribute specifies an absolute virtual address for the function or variable. Be sure to specify the address attribute using an appropriate virtual address. For data variables, the address is typically in the range [0xA0000000,0xA00FFFFC]. For program functions, the address is typically in the range [0x9D000000,0x9D0FFFFC]. A linker relocation error may indicate an out-of-range address.

     This attribute can be used in conjunction with a `section` attribute. This can be used to start a group of variables at a specific address:
     `int foo __attribute__((section("mysection"),address(0xA0001000)));
     int bar __attribute__((section("mysection")));
     int baz __attribute__((section("mysection")));
     __attribute__((address(0x9D00800))) void funky (char* parm)`

     Note that the "small" data and bss (.sdata, .sbss, etc.) sections used for GP-relative addressing are mapped in the built-in linker script. This is because "small" data variables must be grouped together so that they are within range of the more efficient GP-relative addressing mode. To avoid conflict with these linker-script mapped sections, choose high addresses for your absolute-address variables.

     Read More...

     - Notes

       - `GP-Relative addressing` -- The compiler will not use gp-relative addressing for variable attributed with an absolute address. This means that the compiler may generate slightly less efficient code to access these variables.

       - `Error checking` -- There is no error checking on the address. The section will be located at the specified address regardless of the memory-region ranges specified in the linker script or the actual ranges on the target device. The application code is responsible for ensuring that the address is valid for the target device.

       - `Common` -- Variables with the address attribute will not be located in the standard common section.

   - `space`(space) C Attribute for Variables -- Normally, the compiler allocates variables in general data space. Use the space attribute to direct the compiler to allocate a variable in a specific memory space. In this release, the compiler accepts two space attributes: `prog` and `data`. The `prog` space tells the toolchain to allocate the variable to the program memory space (the memory region named kseg0_program_memory in the linker script). The `data` space tells the toolchain to allocate the variable to the data memory space (region kseg1_data_mem).

     Note that when combining the space attribute with the address attribute, the section will be placed at the address specified in the address attribute, but the generated code will use the specified space attribute. The application code must ensure that the combination makes sense for the application.

     `unsigned int foo __attribute__((space(prog))) = 1;
     unsigned int vb __attribute__((space(data))) = 2;
     unsigned int baz __attribute__((space(data)));
     `

   - `ramfunc` C Attribute for Functions -- This new attribute places a function into data memory. Previous releases relied on a magic section name, .ramfunc, and data-memory mapping in the linker script. The new ramfunc attribute places the function at the highest appropriately aligned address. Note that due to ramfunc alignment and placement requirements, the address attribute should not be used with the ramfunc attribute. The presence of a ramfunc section causes the linker to emit the symbols necessary for the crt0.S startup code to initialize the bus matrix appropriately. Use this new attribute along with the far/longcall attribute.

     `__attribute__((ramfunc,section(".ramfunc"),far,unique_section)) unsigned int myramfunct (void)
     {
     // code
     }
     `

     A macro in the sys/attribs.h header file makes the attributes simple to use:
     `#include <sys/attribs.h>
     __longramfunc__ unsigned int myramfunct (void)
     {
     // code
     }
     `

   - `persistent` C Attribute for Variables -- The new `persistent` attribute specifies that the variable should not be initialized or cleared at startup. Use a variable with the `persistent` attribute to store state information that will remain valid after a device reset. The persistent attribute causes the compiler to place the variable in special .bss-like section that does not get cleared by the default startup code. Because the section is always in data space, this attribute is not compatible with the space() attribute.

     `int last_mode __attribute__((persistent));`

   - `-mtext=`"scn-name" Compiler Command-line Option -- Specifying `-mtext=`scn-name will cause text (program code) to be placed in a section named scn-name rather than the default .text section. No white spaces should appear around the =. This command can be useful when developing a bootloader.

     `pic32-gcc bootloader.c -mtext="MySectionName,address(0x9D001000)" -mprocessor=32MX795F512L`

   - New `.section` Assembly-code Directive -- The .section directive now accepts a list of attributes rather than a set of quoted flags. Quoted section flags are now deprecated.

     Read More...

     Syntax: `.section` name `[`, attr1`[`,...,attrn`]]`

     Currently supported section-type attributes:

     - code - Executable code or constant data in program memory
     - data - Initialized storage in data memory
     - bss - Uninitialized storage in data memory
     - persist - Persistent storage in data memory
     - ramfunc - Executable code in data memory

     Currently supported modifier attributes:

     - address(a) - Locate at absolute address a
     - info - Do not allocate or load

   - Linker Allocation Algorithm -- In order to effectively make use of memory with the presence of absolute sections, the linker now uses a best-fit allocator. Note that many standard sections, previously mapped in the default built-in linker script, are now handled by the best-fit allocator. Please see the Migration Issues topic below for important information regarding application-specific linker scripts and startup code.

     Linker allocation steps

     1. Mapping input sections to output sections
     2. Assigning output sections to regions
     3. Allocating unmapped sections

     Read More...

     Steps 1 and 2 are performed by the sequential memory allocator. Input sections which appear in the linker script are assigned to specific memory regions in the target devices. Addresses within a memory region are allocated sequentially, beginning with the lowest address and growing upwards.

     Step 3 is performed by a best-fit memory allocator. Input sections that do not appear in the linker script are assigned to memory regions according to their attributes. The best-fit allocator makes efficient use of any remaining memory, including gaps between output sections that may have been left by the sequential allocator.

     Ramfunc attributed sections are allocated by the best-fit allocator in step 3. Sections designated with the ramfunc attribute should not appear in the linker script as there are special location and alignment requirements for executable code in RAM.

     Absolute sections - When specifying an absolute section (using either the C or assembly address attribute), the application code must take care not to use the same memory as a section mapped in the linker script. This would result in a linker error.

     To help avoid this situation, the default linker script no longer maps most standard sections such as the .text, .data, .bss, or .ramfunc section. By not mapping these sections in the linker script, we allow these sections to be allocated using the new best-fit allocator rather than the sequential allocator.

     The exception is the "small" data sections used for gp-relative addressing. Because these sections must be grouped together, they are mapped in the linker script. A future toolchain release may allow the "small" data sections to be allocated by the best-fit allocator.

   - Data Initialization using a Template and Updated Startup Code -- The linker now generates a data-initialization template (.dinit section) that the startup code uses to initialize variables in data sections. In previous releases, initialized data sections were sequentially allocated so a simple block copy was sufficient. However, since this release supports variables at absolute addresses, a new data-initialization template is required to initialize non-contiguous data sections.

     The linker places the initialization template in the .dinit section. The crt0.S startup code has been updated to initialize data using the new template rather than a block copy. The old startup code will not initialize data properly using this version of the language tools.

   - Stack and heap allocation -- The stack and heap are now dynamically generated. Previous releases used output sections specified in the linker script to allocate the stack and heap. The linker now finds the largest available gap in memory and uses that gap for the heap and stack.

     As in earlier versions, the `_min_stack_size` and `_min_heap_size` linker symbols define the minimum size of the stack and the size of the heap. The size specified for the heap is the exact size to be allocated while the size allocated for the stack is the minimum size allocated.

     The linker-generated memory usage report now displays these dynamically allocated stack and heap areas. Because the stack expands in size to use the entire gap, the total is not added in to the total data memory usage. Only the minimum stack size specified by the application is added to the total.

     `pic32-gcc sourcecode.c -Wl,--defsym,_min_stack_size=2048,--defsym,_min_heap_size=1024`

     `pic32-gcc object1.o object2.o -Wl,--defsym,_min_heap_size=1024,--report-mem -omyproject.elf`

   ## New Features in v1.12

   - Default short double type -- The compiler now uses a 32-bit double type by default. This change makes the PIC32 compiler more consistent with the compiler for PIC24 MCUs and dsPIC DSCs. You can restore the 64-bit double type using the `-fno-short-double` compiler option.

   - Standard C Library -- This release introduces a new version of Lib C that features a generally smaller footprint than previous the lib C. Microchip is in the process of standardizing on one lib C implementation across all first-party compilers. This standardization will smooth your migration path both up and down the Microchip MCU product line, allowing you to more easily move between MCU product lines as your application requirements evolve. The compiler uses the new lib C by default. See the Migration Issues topic for more information.

   - Smart IO v2 -- Previous compiler releases detected floating-point and non-floating point conversion specifiers in calls to formatted IO functions. The toolchain then linked either a full function or an integer-only function as appropriate for your application.

     Version 2 of the smart-IO feature now differentiates between additional types of conversion specifiers. This allows the toolchain to provide a more finely tuned implementation of the formatted IO function that closely matches your application's requirements thereby resulting in in additional code-size improvements.

   - stdout to UART 1 -- The C32 stdio library also now support C30-style UART output. By default stdin/out goes to UART2 for use on the Explorer 16 board or other boards that may use UART2. The application may now use `__C32_UART = 1;` to have stdin/out redirected to use UART1 instead. Currently, the mechanism supports only UART1 and UART2.

     For stdout, the application may provide an application-specific implementation of write(), _mon_write(), or _mon_putc(). Likewise for stdin, the application may provide an application- specfic implementation of read() or _mon_getc(). The default source files for these functions are provided in pic32-libs\libc\stubs. You may wish to extend or customize the code by adding a copy to your project.

   ## New Features in v1.11(b)

   - Part-Support Update -- The v1.11(b) release is a part-support update only. The part-support files (header files, linker scripts, processor libraries) for several devices have been updated. In addition, this release contains updated peripheral libraries. See the peripheral-library documentation for further details.

   ## New Features in v1.11(a)

   - Builtin functions for CP0 register access -- This release introduces a few new compiler builtin functions that simplify access to the PIC32 coprocessor 0 (CP0) registers. Combine these new builtin functions with macros defined in the cp0defs.h and p32xxxx.h header files for easy access to the various CP0 registers.

     In earlier compiler releases, the p32xxxx.h header file defined _mfc0/_mtc0 preprocessor macros that utilized extended inline assembly to generate the mfco and mtc0 instructions. These _mfc0 and _mtc0 macros are updated to utilize the new builtin funtions instead of inline assembly.

     NOTE: To access these CP0 registers, the compiler must generate assembly instructions (mfc0 & mtc0) that are supported in only the mips32 ISA mode. Therefore, when calling one of these functions from a mips16 function, the compiler must generate extra code to switch from mips16 mode back to the base mips32 mode before executing the instruction and then back to mips16 mode after executing the instruction.

     Read More...

     - `unsigned int __builtin_mfc0(reg,sel)`
         Returns the value from the CP0 register `reg,sel`. (Move From Coprocessor 0.) Both `reg` and `sel` must be immediate values.

         Example 1:
         `val = __builtin_mfc0 (12,0);`

         Example 2:
         `#include <cp0defs.h>
         void funct (void) {
         unsigned int val;
         val = __builtin_mfc0 (_CP0_STATUS,_CP0_STATUS_SELECT);
         }`

     - `void __builtin_mtc0(reg,sel,value)`
         Move `value` into the CP0 register`reg,sel`. (Move To Coprocessor 0.) Both `reg` and `sel` must be immediate values.

         Example 1:
         `__builtin_mtc0 (12,0,0x00100000u);`

         Example 2:
         `#include <cp0defs.h>
         void funct (void) {
         unsigned int val;
         /* code here */
         __builtin_mtc0 (_CP0_STATUS,_CP0_STATUS_SELECT,val);
         }`

     - `unsigned int __builtin_mxc0(reg,sel,value)`
         Exchange/Swap `value` and the CP0 register `reg,sel`. Move `value` to the CP0 register `reg,sel` and return the previous value. Both `reg` and `sel` must be immediate values.

         Example 1:
         `oldval = __builtin_mxc0 (12,0,0x00100000u);`

         Example 2:
         `#include <cp0defs.h>
         void funct (void) {
         unsigned int newval, oldval;
         /* code here */
         oldval = __builtin_mxc0 (_CP0_STATUS,_CP0_STATUS_SELECT,newval);
         }`

     - `unsigned int __builtin_bcc0(reg,sel,clr)`
         Bit clear non-zero bits from `clr` in the CP0 register `reg,sel` and return the previous value of the CP0 register. Both `reg` and `sel` must be immediate values.

         Example:
         `#include <cp0defs.h>
         void funct (void) {
         unsigned int clear, oldval;
         /* code here */
         oldval = __builtin_bcc0 (_CP0_STATUS,_CP0_STATUS_SELECT,clear);
         }`

         This is equivalent to
         `oldval = __builtin_mfc0 (_CP0_STATUS,_CP0_STATUS_SELECT);
         __builtin_mtc0 (_CP0_STATUS,_CP0_STATUS_SELECT, oldval & ~(clear));`
         but the bcc0 builtin may generate more efficient code, especially when called from mips16 mode.

     - `unsigned int __builtin_bsc0(reg,sel,set)`
         Bit set non-zero bits from `set` in the CP0 register `reg,sel` and return the previous value of the CP0 register. Both `reg` and `sel` must be immediate values.

         Example:
         `#include <cp0defs.h>
         void funct (void) {
         unsigned int set, oldval;
         /* code here */
         oldval = __builtin_bsc0 (_CP0_STATUS,_CP0_STATUS_SELECT,set);
         }`

         This is equivalent to
         `oldval = __builtin_mfc0 (_CP0_STATUS,_CP0_STATUS_SELECT);
         __builtin_mtc0 (_CP0_STATUS,_CP0_STATUS_SELECT, oldval | (set));`
         but the bsc0 builtin may generate more efficient code, especially when called from mips16 mode.

     - `unsigned int __builtin_bcsc0(reg,sel,clr,set)`
         Bit clear non-zero bits from `clr` and bit set non-zero bits from `set` in the CP0 register `reg,sel`. Return the previous value of the CP0 register. Both `reg` and `sel` must be immediate values.

         Example:
         `#include <cp0defs.h>
         void funct (void) {
         unsigned int clr, set, oldval;
         /* code here */
         oldval = __builtin_bcsc0 (_CP0_STATUS,_CP0_STATUS_SELECT,clr,set);
         }`

         This is equivalent to
         `oldval = __builtin_mfc0 (_CP0_STATUS,_CP0_STATUS_SELECT);
         __builtin_mtc0 (_CP0_STATUS,_CP0_STATUS_SELECT, (oldval & ~(clr)) | (set));`
         but the bcsc0 builtin may generate more efficient code, especially when called from mips16 mode.

   - Upgrade to binutils v2.19 -- The MPLAB Assembler, Linker, and Utilities for PIC32 MCUs are now based on GNU Binutils v2.19. This platform upgrade includes a few new features and bug fixes.

     - Assembler
       - Macros with a variable number of arguments are now supported. See the Binutils documentation for more information.
       - A redefinition of a macro now results in an error.
       - The assembler sources are now released under version 3 of the GNU General Public License.
     - Linker
       - Added a new linker command-line switch, `--sort-section name|alignment`, to sort sections by section name or maximum alignment.
       - Added `SORT_BY_NAME` and `SORT_BY_ALIGNMENT` to the linker script language to permit sorting sections by section name or section maximum alignment.
       - New switch: `--print-gc-sections` to list any sections removed by garabge collection.
       - Addded a new command-line option '`--default-script=FILE`' or '`-dT FILE`' which specifies a replacement for the built-in, default linker script.
       - Linker scripts support a new `INSERT` command that makes it easier to augment the default script.
       - Linker-script input-section filespecs may now specify a file within an archive by writing "archive:file".
       - The `--sort-common` switch now has an optional argument which specifies the direction of sorting.
       - The Linker sources are now released under version 3 of the GNU General Public License.
     - Binary Utilities
       - pic32-readelf can now display address ranges from .debug_range sections. This happens automatically when a DW_AT_range attribute is encountered. The command line switch `--debug-dump=Ranges` (or `-wR`) can also be used to display the contents of the .debug_range section.
       - pic32-objcopy recognizes two new options, `--strip-unneeded-symbol` and `--strip-unneeded-symbols`, namely for use together with the wildcard matching the original `--strip-symbol`/`--strip-symbols` provided, but retaining any symbols matching but needed by relocations.
       - Added `-g`/`--section-groups` to pic32-readelf to display section groups.
       - Added `--globalize-symbol <name>` and `--globalize-symbols <filename>` switches to pic32-objcopy to convert local symbols into global symbols.
       - Added `-t`/`--section-details` to pic32-readelf to display section details
       - Added `-W`/`--dwarf` to pic32-objdump to display the contents of the DWARF debug sections.
       - Added `-wL` switch to dump decoded contents of .debug_line.
       - Added `-F` switch to pic32-objdump to include file offsets in the disassembly.
       - Added `-c` switch to pic32-readelf to allow string dumps of archive symbol index.
       - Added `-p` switch to pic32-readelf to allow string dumps of sections.
       - The Binutils sources are now released under version 3 of the GNU General Public License.

   - RIPL Interrupt Priority Level specifier -- The v1.10 release introduced new Interrupt Priority Level specifiers. It also introduced a new default IPL behavior when the IPL specifier was omitted from the interrupt attribute. (See New Features in v1.10 below for more information.)

     The v1.11 release introduces an explicit specifier (RIPL) for this default behavior. You may use this RIPL specifier in either the interrupt pragma or the interrupt attribute to tell the compiler to use the runtime Requested Interrupt Priority Level from the CAUSE register as the new IPL.

     - Example 1:

       `#pragma interrupt Timer1IntHandler RIPL vector 4`

     - Example 2:

       `void __attribute__((interrupt(RIPL), vector(1))) myISR (void)) { /* code */ }`

   ## New Features in v1.10

   - Compiler licenses renamed -- The compiler license editions have been renamed. The academic version is now the MPLAB C Compiler for PIC32 MCUs Lite edition. The evaluation version is now the MPLAB C Compiler for PIC32 MCUs Standard Evaluation edition. The full version is now the MPLAB C Compiler for PIC32 MCUs Standard edition (Part Number: SW006015). This is a name change only. See this section for more information on the features available for each edition.

   - Smart I/O -- This release introduces a new `-msmart-io=[0|1|2]` command-line option. This feature attempts to statically analyze format strings passed to `printf`, `scanf`, and the 'f' and 'v' variations of these functions. Uses of non floating-point format arguments will be converted to use an integer-only variation of the library function. For many applications, this feature can reduce program-memory usage.

     `-msmart-io=0` disables this option, while `-msmart-io=2` causes the compiler to be optimistic and convert function calls with variable or unknown format arguments. `-msmart-io=1` is the safe default and will convert only when the compiler can prove that floating-point support is not required.

   - Interrupt Context-Saving Improvements -- New PIC32 devices introduced in this release (PIC32MX5, PIC32MX6, PIC3MX7) allow us to select, via configuration fuses, which priority will use the shadow register set. (Refer to the device datasheet to determine if your PIC32 device supports this feature.) This means that we must specify which context-saving mechanism to use for each interrupt service routine. We specify the mechanism as part of the IPL specifier passed in the interrupt attribute, `__attribute__((interrupt([IPLn[AUTO|SOFT|SRS]])))`, where n is in the range of 0..7, inclusive.

     NOTE: An incorrect `IPLn` value can cause incorrect nesting of interrupts, which could result in a stack overflow and eventually a bus-error exception. If you experience a bus-error exception related to an interrupt, double check that your `IPLn` value matches the IPL value set for the interrupt source.

     Read More...

     - IPL Specifiers

       - `IPLnAUTO` -- The compiler supports an `IPLnAUTO` IPL specifier that uses the runtime value in `SRSCTL` to determine whether it should use software or SRS context saving. The interrupt context-saving code generated for this specifier has a slightly higher latency, compared to `IPLnSOFT` or `IPLnSRS`, due to the instructions required to test the `SRSCTL` value. Example:
         `void __attribute__((interrupt(IPL6AUTO), vector(1))) myISR (void)) { /* code */ }`

       - `IPLnSOFT` -- The compiler will use software context saving for the `IPLnSOFT` specifier. Application code is responsible for applying the correct n interrupt-source priority value to the matching handler routine. Example:
         `void __attribute__((interrupt(IPL6SOFT), vector(1))) myISR (void)) { /* code */ }`

       - `IPLnSRS` -- The compiler will generate interrupt prologue and epilogue code utilizing shadow-register context saving for `IPLnSRS`. This IPL specifier results in the shortest interrupt context-saving latency. However, when using `IPLnSRS`, you must configure the corresponding interrupt source to use a shadow register set. On some devices, the shadow register set is tied to IPL7. On other devices, the shadow register set is configurable in a device configuration register (DEVCFG). Example:
         `void __attribute__((interrupt(IPL6SRS), vector(1))) myISR (void)) { /* code */ }`

       - `single` -- For single-vector interrupt mode, use `single` as the IPL parameter passed to the interrupt attribute. Example:
         `void __attribute__((interrupt(single), vector(1))) myISR (void)) { /* code */ }`

       - Default -- The compiler defaults to selecting the IPL value and shadow-register usage at runtime when the IPL specifier is omitted from the interrupt() attribute. Omitting the IPL specifier results in slightly larger interrupt context-saving latency. For mult-vector interrupt mode where the requested IPL value may change at runtime, use this default behavior. Example:
         `void __attribute__((interrupt(), vector(1))) myISR (void)) { /* code */ }`

     - Updated __ISR Macro -- The IPL specifier argument to the `__ISR()` macro, defined in `<sys/attribs.h>`, is now optional. With the IPL specifier omitted, the compiler defaults to selecting the IPL value and shadow-register usage at runtime.

       - Example 1
         `void __ISR(_CORE_SOFTWARE_0_VECTOR, IPL3SRS) CoreSoftwareInt0Handler(void)`
         This example creates an interrupt handler function for the core software interrupt 0 that has an interrupt priority level of three. The compiler places a dispatch function at the associated vector location. To reach this function, the core software interrupt flag and enable bits must be set, and the interrupt priority should be set to a level of three. The device configuration fuses must assign Shadow Register Set 1 to interrupt priority level three. The compiler generates code that assumes that register context will be saved in SRS1.

       - Example 2
         `void __ISR(_CORE_SOFTWARE_0_VECTOR) CoreSoftwareInt0Handler(void)`
         This example creates an interrupt handler function for the core software-interrupt 0 and uses the interrupt priority level from the runtime-requested IPL value. The compiler generates code that determines, at runtime, whether context should be saved on the stack by software or context was already saved in a shadow register set.

     - Latency improvements -- The interrupt context saving code has also been modified to improve latency. For instance, the HI/LO register saving code, when required, now appears later in the ISR prologue. This helps reduce stalls when an interrupt occurs during a DIV (divide) instruction.

   - APPIN/APPOUT Debugging Support -- New PIC32 devices being introduced in v1.10 (PIC32MX5, MX6, MX7) support the APPIN/APPOUT debugging feature. This PIC32 feature allows the target application to write text or data to an MPLAB IDE window without halting the target device. Similarly, you may use the display window to send text or data back to the target PIC32 device. This feature requires an MPLAB REAL ICE emulator or an MPLAB ICD 3 debugger.

     Read More...

     - `-mappio-debug` -- Use this command-line option to enable the APPIN/APPOUT debugging library functions for the ICD 3 debugger and REAL ICE emulator. This feature allows you to use the DBPRINTF and related functions and macros. Enable this option only when using a target PIC32 device that supports the APPIN/APPOUT feature.
     - Example Code --

           #include <p32xxxx.h>
           int main (void)
           {
               int num;
               char buf[256] ={0};
               DBINIT();

               while(1)
               {
                 DBPRINTF ("Hello there!\n");
                 DBPRINTF ("Enter a string\n");
           #if defined(__APPIO_DEBUG)
                 DBSCANF ("%s", &buf[0]);
           #elif defined(PIC32_STARTER_KIT)
                 DBGETS  (&buf[0],128);
           #endif
                 DBPRINTF ("Entered \"%s\"\n\n", &buf[0]);

                 printf ("Prints to UART2 by default or APPO when enabled\n");
               }
             return 0;
           }

   - Stack Limit symbol in built-in linker script -- The default linker script now provides an _SPLIM symbol that you can use from code to help detect a stack overflow at runtime. This symbol is associated with the lowest address of the space reserved for the stack.

     Read More...

     - Example Code --

           #include <stddef.h>
           #define _STACK_DEBUG 1
           #if (_STACK_DEBUG)
           #define stackcheck() _stackcheck(__FILE__, __LINE__)

           static inline __attribute__((always_inline))
           ptrdiff_t _stackcheck(const char *filename, unsigned int linenum)
           {
             extern void _SPLIM; /* From linker script */

             register void* stackptr __asm__("$sp");

             /* Compare the current stack pointer with the Stack Pointer Limit symbol, _SPLIM */
             if ((ptrdiff_t)stackptr <= (ptrdiff_t)&_SPLIM)
               {
                   /* Handle stack overflow */
                   while(1);
               }
             return ((ptrdiff_t)stackptr - (ptrdiff_t)&_SPLIM);
           }
           #else
           #define stackcheck() (void)0
           #endif

           unsigned char foo(unsigned char var);
           volatile unsigned int testval;

           int main (void)
           {
               unsigned char array[0x7A50];
               testval = 0;

               array[0] = 1;
               foo (array[0]);

               testval = 1;
               while(1);
           }
           unsigned char
           foo(unsigned char var)
           {
               stackcheck();
               return var+1;
           }

   - Predefined macro for Feature Set -- The compiler predefines a macro based on the features available for the selected device. These macros are intended to be used when writing code to take advantage of features available on newer devices while maintaining compatibility with older devices.

     Read More...

     - Examples
       PIC32MX795F512L would use `__PIC32_FEATURE_SET__ == 795`, and
       PIC32MX340F128H would use `__PIC32_FEATURE_SET__ == 340`.
     - Example Code --

           #if ((__PIC32_FEATURE_SET__ >= 500) &&
                (__PIC32_FEATURE_SET__ <= 799))
              { /* do stuff for 5XX, 6XX, 7XX families */ }
           #elif ((__PIC32_FEATURE_SET__ >= 300) &&
                  (__PIC32_FEATURE_SET__ <= 499))
              { /* do stuff for 3XX, 4XX families */ }
           #elif ((__PIC32_FEATURE_SET__ >= 800) &&
                  (__PIC32_FEATURE_SET__ < 1000))
              { /* do stuff for some future family */ }
           #endif

   ## New Features in v1.05

   - Student Edition renamed Evaluation Version -- The student edition has been renamed the evaluation version. This release also introduces a new academic version. For more information on the edition, see this section. (Note that the licenses have been renamed again for the v1.10 release.)
   - Improved 16- and 32-bit FFT functions in the DSP Library -- The FFT functions have been significantly improved and optimized for the PIC32 instruction set. See the 32-bit Language Tools Libraries document (DS51685) for more information. Please visit Microchip's website for the revision C of this document (DS51685C).
   - Binary Constants -- A sequence of binary digits preceded by 0b or 0B (the numeral '0' followed by the letter 'b' or 'B') is taken to be a binary integer. The binary digits consist of the numerals '0' and '1'. Note that this binary-constant syntax may not be accepted by other C compilers.
   - Linker Memory-Usage Report -- This optional, informational report allows you to easily determine the program- and data-memory usage of your application. It allows you to see how much space is used by the project being linked and how much space is available on the target device. The memory-usage report appears on stdout and in the optional map file.
     - Using this feature with MPLAB IDE 8.30 and earlier -- On the linker's tab of the project build options, select to Use Alternate Settings. Add the `--report-mem` option to the Alternate Settings field. The memory-usage report will appear in the output window after a project build. (This option will appear as a checkbox in later MPLAB IDE releases.)
     - Using this feature on the command prompt -- Add the `--report-mem` option to the linker's command line. If you are calling the linker via the compilation driver, use the driver's `-Wl` option to pass the `--report-mem` option to the linker. The memory-usage report will appear on stdout.
   - Improved malloc implementation -- This release contains a new malloc/free/realloc implementation based on the implementation written by Doug Lea and released to the public domain. (Note that C32 v1.12 introduces another implementation.)
     - This is not the fastest, most space-conserving, most portable, or most tunable malloc ever written. However it is among the fastest while also being among the most space-conserving, portable and tunable. Consistent balance across these factors results in a good general-purpose allocator.
     - For a high-level description, see http://g.oswego.edu/dl/html/malloc.html
     - This implementation is also provided with the Newlib C Library.
   - Instruction Macros -- The p32xxxx.h include file now contains a Nop() macro that issues a superscalar SSNOP instruction.
   - `gettimeofday()` weak stub -- The time.h `clock()` and `time()` functions require a user-provided `gettimeofday()` helper function. The compiler's library now provides a weak stub implementation that allows the project link to complete without error, but you should provide your own implementation appropriate for your application.
   - Microchip DSP Compatibility Wrapper functions -- This release provides new DSP wrapper functions intended to ease the migration from the Microchip DSP library for dsPIC DSCs to the general DSP library for PIC32 MCUs. See the 32-Bit Language Tools Libraries (DS51685C) document for more information on these new wrapper functions.
   - Updated peripheral-library documentation -- The 32-bit peripheral library document is now distributed as a compiled help file (*.chm) rather than a PDF file.
   - Support for PWP configuration bits -- The config pragma now supports enabling the Program Write Protect bits. See the PIC32MX Config Settings help file for information on the setting name and available values for each device.

7. ## New Features in v1.04

   - General DSP Library -- The DSP Library supports a variety of signal processing functions that have applicability in speech compression, echo cancellation, noise cancellation, channel equalization, audio decoding, and many other DSP and media applications. The library is highly optimized for the PIC32 MCU instruction set.
     - The DSP Library expects Q-type fixed-point arguments and produces Q-type results. The MPLAB C Compiler for PIC32 MCUs does not currently support converting float or double types to Q-types.
     - See the 32-Bit Language Tools Libraries (DS51685) for documentation on the DSP Library functions.
     - In the near future, a "dsPIC DSC DSP Algorithm Library" compatibility layer will be available. This compatibility layer makes the PIC32 DSP Library backwards compatible with the existing dsPIC DSC DSP Algorithm Library.
   - Vector attribute accepts parenthesized list of vector numbers -- The interrupt vector attribute now accepts a parenthesized list of one or more interrupt vector numbers. This means that you can now more easily generate multiple dispatch functions that target a single interrupt service routine as shown in the example below.
     `#include <p32xxxx.h>
     #include <sys/attribs.h>
     void __ISR((_TIMER_1_VECTOR,_TIMER_2_VECTOR,_TIMER_3_VECTOR),ipl6) TimerISR(void);`
   - Interrupt service routines forced to nomips16 -- The compiler will now force functions marked with the interrupt attribute to be nomips16. The compiler will emit a warning if it overrides the mips16 attribute or command-line default. Previous compiler releases stopped compilation with an error and required users to manually add the nomips16 attribute. Note that you should use the __ISR macro from the sys/attribs.h header rather than manually specify the interrupt attribute.
   - Trigonometric function refactorization -- A few trigonometric functions have been refactored for a smaller code-size footprint.

   ## New Features in v1.03

   - Optimized math library -- The floating-point math library provided with the compiler has been significantly optimized to take full advantage of the PIC32 MCU instruction set. The improved library provides the greatest benefit for the more complex operations, offering a greater than 5x performance improvement over the 1.02 library for many operations and an even more significant improvement for some operations. In addition, single-precision math library functions are now available, giving users a choice between double- and single-precision operations. See math.h for more information.
   - Evaluation Version -- The new evaluation edition provides standard-edition functionality for 60 days. After the evaluation version has expired, these additional features are disabled. See this section for further details. (Note that this license has been renamed to the "Standard Evaluation Edition" for the v1.10 release.)
   - `__C32_VERSION__` predefined macro -- The C compiler defines the constant `__C32_VERSION__`, giving a numeric value to the version identifier. This macro can be used to construct applications that take advantage of new compiler features while still remaining backward compatible with older versions. The value is based upon the major and minor version numbers of the current release. For example, release version 1.03 will have a `__C32_VERSION__` definition of 103. This macro can be used, in conjunction with standard preprocessor comparison statements, to conditionally include/exclude various code constructs.
   - `__ISR_SINGLE__` and `__ISR_SINGLE_AT_VECTOR__` convenience macros -- The sys/attribs.h header file now provides two new macros intended to simplify the use of the single-vector interrupt mechanism. See the sys/attribs.h header file for more information.
     - The `__ISR_SINGLE__` macro specifies a function as an interrupt-service routine in single-vector mode. This will place a jump at the single-vector location to the interrupt handler.
     - The `__ISR_SINGLE_AT_VECTOR__` macro places the entire single-vector interrupt handler at the vector 0 location. The user is responsible for ensuring that the vector spacing is set to accommodate the size of the handler.

8. # Migration Issues

   The following changes may affect migration from older versions of the compiler.

   ## Migrating to Version v2.00

   - Compiler

   - - Custom Startup Code -- This release of the toolchain introduces data initialization using a .dinit template and associated startup code. Previous releases relied on a block copy in the startup code that copied from the .data section located in program memory to the .data section allocated in data memory. If your project uses custom startup code and initialized data, replace the block copy in your custom startup code with initialization code utilizing the .dinit template. A copy of the updated default startup code is located in the /pic32-libs/libc/startup/crt0.S file installed with the compiler.

     - Placement of the `mips16`/`nomips16` Function Attribute -- The `mips16` and `nomips16` function attributes are now declaration attributes rather than type attributes. This means that they should be placed at the beginning of a declaration rather than on the type. The compiler will emit a warning message if the attribute should be moved.

       `__attribute__((mips16)) unsigned int *funct1 (void) { /* code */ }`

   - Linker

   - - Custom Linker Script -- To make effective use of absolute sections and the new best-fit allocator, standard program-memory and data-memory sections should not be mapped in the linker script. The built-in linker script no longer maps most standard sections such as the .text, .data, .bss, or .ramfunc section. By not mapping these sections in the linker script, we allow these sections to be allocated using the new best-fit allocator rather than the sequential allocator. Sections that are unmapped in the linker script can flow around absolute sections whereas sections that are linker-script mapped are grouped together and allocated sequentially, potentially causing conflicts with absolute sections.

       Note that the "small" data and bss (.sdata, .sbss, etc.) sections are still mapped in the built-in linker script. This is because "small" data variables must be grouped together so that they are within range of the more efficient GP-relative addressing mode. To avoid conflict with these linker-script mapped sections, choose high addresses for your absolute-address variables.

       New debug information should be mapped to 0 in the linker script. The linker script should map the new .debug_ranges, .debug_pubtypes, and .gnu.attributes sections in the linker script so that they do not get allocated to program or data memory. You can do this by adding two lines to your custom linker script. In the existing linker script, find the output-section command within the SECTIONS block where the other .debug sections are mapped. Add the two lines for .debug_ranges and .debug_pubtypes.

       `/* SGI/MIPS DWARF 2 extensions */
       .debug_weaknames 0 : { *(.debug_weaknames) }
       .debug_funcnames 0 : { *(.debug_funcnames) }
       .debug_typenames 0 : { *(.debug_typenames) }
       .debug_varnames 0 : { *(.debug_varnames) }
       .debug_pubtypes 0 : { *(.debug_pubtypes) }
       .debug_range 0 : { *(.debug_ranges) }
       .gnu.attributes 0 : { KEEP (*(.gnu.attributes)) }
       /DISCARD/ : { *(.rel.dyn) }
       /DISCARD/ : { *(.note.GNU-stack) }
       `

       A copy of the updated built-in linker script is located in /pic32mx/lib/ldscripts/elf32pic32mx.x.

   - Libraries

   - - Peripheral Freeze (FRZ) bits -- The peripheral-library functions no longer modify the debug freeze bit for the corresponding peripheral. Use an in-circuit debugger or emulator to configure the peripheral to freeze when debugging, if required.

   - Installer

   - - Default install location -- The installer now always defaults to installing in a standard installation path. If you do not wish to have multiple versions of the toolchain installed on your machine, uninstall the previous versions.

       Windows
         C:\Program Files\Microchip\mplabc32\<version>
       Linux
         /opt/microchip/mplabc32/<version>
       Mac OS X
         /Applications/microchip/mplabc32/<version>

   ## Migrating to Version v1.12

   - Compiler

   - - Default double type -- As indicated above in the "What's New section, in order to improve the migration path between C30 and C32, this release changes the default size of the `double` type from 64 bits to 32 bits. The `long double` type remains 64 bits. You may also restore default double size to 64 bits by passing the -fno-short-double option to the compiler.

       Warning: This change means that the compiler will generate code that is not binary compatible with code generated using the 64-bit double. All object files in a project should be generated with the same double size.

   - Libraries

   - - Standard C Library -- This release features a new lib C that can reduce the footprint of applications that make use of these library functions. There are significant differences in the implementation of functions such as printf() and malloc(). In addition, lldiv_t and strtok_r() are not yet supported in this library.

       For customers wishing to continue to use the version of lib C provided by earlier versions of MPLAB C32, the compiler option `-legacy-libc` makes this easy to manage. Be sure to pass the `-legacy-libc` option to pic32-gcc when both compiling and linking. In MPLAB IDE v8, find a checkbox for this option in the project build options, under the library selection category of the linker tab.

   ## Migrating to Version v1.11

   - Linker
   - - Allocation of orphan sections -- Orphan sections are sections present in the input files which are not explicitly placed into the output file by the linker script. The linker will still copy these sections into the output file, but it has to guess as to where they should be placed. The linker uses a simple heuristic to do this. It attempts to place orphan sections after non-orphan sections of the same attribute, such as code vs data, loadable vs non-loadable, etc. If there is not enough room to do this then it places at the end of the file.

       If an orphaned section's name is representable as a C identifier then the linker will automatically PROVIDE two symbols: __start_SECNAME and __end_SECNAME, where SECNAME is the name of the section. These indicate the start address and end address of the orphaned section respectively. Note: most section names are not representable as C identifiers because they contain a `.' character.

       Note: In previous releases, the linker allocated orphan sections at a high address, after all other sections had been allocated. This is no longer the case and applications should not rely on orphan sections being uninitialized.

   - Default Linker Script
   - - New .persist section -- The default linker script now provides a .persist section between the .stack section and the .ramfunc section. This section is not initialized or zeroed on startup. If your project used a custom section for this purpose, you can now utilize this new .persist section that is specifically mapped outside of the .bss and .data sections.
       Example:
       `unsigned int __attribute__((section(".persist"))) flag;`

   ## Migrating to Version v1.10

   - Interrupt context saving
     - IPL specifier -- In prior compiler releases, the interrupt service-routine prologue code determined the IPL value from the runtime RIPL value. This meant that the IPL specifier value in the interrupt attribute or interrupt pragma did not have to exactly match the actual IPL value for the interrupt source. The interrupt service routine worked correctly, even when there was a discrepancy in the IPL value.

       The interrupt prologue code generated by this release of the compiler uses the IPL value as specified in the interrupt attribute or interrupt pragma. An incorrect IPLn value can cause incorrect nesting of interrupts, which could result in a stack overflow and eventually a bus-error exception. If you experience a bus-error exception related to an interrupt, double check that your IPLn value matches the IPL value set for the interrupt source.

       Some applications may require an interrupt priority that changes at runtime. In this case, omit the IPL specifier from the interrupt attribute as shown in the examples below. e.g.
       `void __attribute__((interrupt(), vector(1))) myISR1 (void)) { /* code */ }`
       `void __ISR(_CORE_SOFTWARE_0_VECTOR) CoreSoftwareInt0Handler(void) { /* code */ }`

       Currently, the interrupt pragma does not support interrupt priority levels that change at runtime. In this case, convert the interrupt pragma to an interrupt attribute as described above. For instance:

           #pragma interrupt foo ipl3 vector 4
           void foo (void) { /* code */ }

       becomes

           void __attribute__((interrupt(), vector(4))) foo (void) { /* code */ }

   - STDIO
     - BUFSIZ -- The input buffer size has been reduced from 1024 to 64 bytes. Use the setvbuf() function to specify another buffer if your application requires a buffer of another size.
     - STDOUT_BUFSIZ -- The stdout default-buffer size has been reduced from 128 bytes to 32 bytes. Use the setvbuf() function to specify another buffer if your application requires a buffer of another size.
   - Device support
     - PIC32MX4xx devices -- The UPLLIDIV configuration fuse settings were incorrectly named DIV_7 and DIV_8 for several PIC32MX4XX devices. They are now correctly named DIV_10 and DIV_12, respectively. Code using the older names will fail to compile. Update your code to use the new setting names.
   - Documentation
     - Peripheral Library documentation now provided as a help file -- The peripheral library documentation is now provided as a CHM file rather than a PDF file. Older versions of the compiler installer added a link to the PDF file in MPLAB IDE's online help. To remove this outdated link, run the uninstall facility in Windows Add/Remove Programs to completely uninstall the compiler. Then re-run the v1.10 compiler installer.

   ## Migrating to Version v1.05

   - DSP Library
     - FFT setup functions -- The FFT setup functions, mips_fft16_setup() and mips_fft32_setup(), are now deprecated. The FFT functions now load precalculated coefficients so these setup functions are no longer required. Please visit Microchip's website for the revision C of the 32-bit Libraries document (DS51685C).

   ## Migrating to Version v1.04

   - Device-support files
     - Device specific IRQ macro definitions -- The IRQ macro definitions, such as `_CORE_TIMER_IRQ`, have moved from the ppic32mx.h header file to the device-specific header file (e.g. proc/p32mx460f512l.h). This change should not affect most applications because they should include the generic p32xxxx.h file.

   ## Migrating to Version v1.03

   - Peripheral Library
     - Modified SYSTEMConfigXXX functions to use revised flash speed of 30 MHz. If you are currently using a SYSTEMConfigXXX function, your application will automatically use the new flash-speed specification.
   - Examples
     - Modified all plib_examples to use SYSTEMConfig() function. This function allows users to selectively configure certain parameters only.

   ## Migrating to Version v1.02

   - Processor Header files
     - Removed Extended Mode (XM bit) in DMA controller
   - Peripheral Library - See the Microchip PIC32MX Peripheral Library compiled help (*.chm) for details
     - DMA Extended mode is removed. The maximum transfer length is now 256 bytes, even for memory copy and CRC functions.
     - Symbols DMA_OPEN_NORM and DMA_OPEN_EXT used in the DmaChnOpen() call were removed. A new symbol, DMA_OPEN_DEFAULT was added.
     - A new function, DmaGetMaxTcferSize() was added, to return the maximum supported size of a transfer, variant dependent. Right now, only 256 bytes transfer size supported.
     - DmaChnSetExtTxfer() was removed, no longer relevant.
     - DMA_CTL_EXT_EN was removed from the low level access routines
     - SYSTEMConfig() function was added to enable user-specified configuration for a given system frequency.

9. # Documentation Updates

   ## Library documentation updates

   This section describes pending updates to the MPLAB® 32-Bit Language Tools Libraries documentation. These changes will be incorporated into the next full revision of the documents.

   - BUFSIZ -- The BUFSIZ definition in stdio.h has been reduced to 32.

   ## Compiler documentation updates

   This section describes pending updates to the MPLAB C Compiler for PIC32 documentation. These changes will be incorporated into the next full revision of the documents.

   - Address and Space C attributes -- The address and space attributes will be added to the compiler user's guide. For now, please see the What's New and Migration Issues sections of this file.
   - C Startup Code -- Changes related to .dinit data initialization template will be added to the compiler user's guide. For now, please see the What's New and Migration Issues sections of this file.
   - Binary Constants -- A sequence of binary digits preceded by `0b` or `0B` (the numeral '0' followed by the letter 'b' or 'B') is taken to be a binary integer. The binary digits consist of the numerals '0' and '1'. For example, the (decimal) number 255 can be written as `0b11111111`. Like other integer constants, a binary constant may be suffixed by the letter 'u' or 'U', to specify that it is unsigned. A binary constant may also be suffixed by the letter 'l' or 'L', to specify that it is long. Similarly, the suffix 'll' or 'LL' denotes a long long binary constant. Note that this binary-constant syntax may not be accepted by other C compilers.
   - `__VERSION__` predefined macro -- The `__VERSION__` macro expands to a string constant describing the compiler in use. Do not rely on its contents having any particular form, but it should contain at least the release number. Use the `__C32_VERSION__` macro for a numeric version number.
   - Interrupt-vector macros -- Each processor-support header file (e.g. \pic32mx\include\proc\p32mx360f512l.h) provides a macro for each interrupt-vector number. When used in conjunction with the `__ISR()` macro provided by the sys\attribs.h header file, these macros help make an interrupt service routine easier to write and maintain. Example: `void __ISR (_TIMER_1_VECTOR, ipl7) Timer1Handler (void);`

   ## Assembler/Linker/Utilities documentation updates

   This section describes pending updates to the MPLAB Assembler, Linker and Utilities for PIC32 MCUs User's Guide (DS51833) documentation. These changes will be incorporated into the next full revision of the documents.

   - `.section` Assembler Directive -- The new .section directive with attributes will be documented in the user's guide. For now, please see the What's New and Migration Issues sections of this file.
   - Linker Allocation Algorithm -- The improved allocation algorithm featuring best-fit allocation will be documented in the user's guide. For now, please see the What's New and Migration Issues sections of this file.

10. # Fixed Issues

    The following issues have been resolved in this release

    ## Fixed in v2.01

    C32-491:
      The watchdog timer (WDT) should now clear correctly on devices when the WDT Enable config bit is set using the config pragma. MPLAB C32 v2.00 incorrectly set some unimplemented bits to '0' rather than '1', which could cause problems with the WDT.
    C32-490:
      The single-precision atan2(y,x) function now returns the correct -Pi/2 value for the boundary condition (y<0 && x==0)
    C32-489:
      Compatibility issues related to the BigInt_helper_C32.S assembly code file in the Microchip TCP/IP stack have been resolved.
    C32-487:
      The _UART2_BASE_ADDRESS definition in the PIC32MX3 and MX4 device-support header files have been corrected. This caused the UART2 peripheral library functions to write to unimplemented locations rather than the correct Special Function Register addresses.
    C32-483:
      The C runtime startup code now correctly clears global uninitialized variables allocated to the "common" section.
    C32-480:
      The malloc free() function now handles a NULL pointer more gracefully. In previous releases, calling free() with a NULL pointer could cause heap corruption. In addition, the malloc() function now uses a smaller block size. This results in more efficient heap usage for most embedded applications.
    BIN32-79:
      The linker no longer marks the .sdata section as LOADable. In the MPLAB C32 v2.00 release, the .sdata section appeared in the hex file causing a problem for some hex file consumers.
    BIN32-77:
      The linker no longer causes a segmentation fault on projects that use the .rel.dyn section. Dynamic relocations are not yet supported.
    BIN32-76:
      The linker no longer emits symbols causing the bus matrix to be initialized when ram functions do not exist in the project. MPLAB C32 v2.00 always initialized the bus matrix, potentially causing runtime problems for projects using a custom linker script with a data section that did not end on a 2K aligned address.

    ## Fixed in v2.00

    C32-412:
      Peripheral library function-like macros related to 32-bit timers TMR23 and TMR45 are restored. In the v1.12 release, these macros were unavailable and caused a link error for application code that attempted to use them. These macros are now again available on appropriate devices.
    C32-391:
      Some errors related to smart-io version 2 are now corrected. In the v1.12 release, some uses of formatted IO functions could cause a linker error along the lines of "undefined reference to `_fprintf_s' ". This error has been corrected for v2.00.
    C32-390:
      Library functions asprintf() and vasprintf() should now link correctly.
    BIN32-73:
      A potential linker hang/crash related to smart IO has been corrected.

    ## Fixed in v1.12

    C32-350:
      The compiler now always preserves the $ra register when a function calls the __builtin_mfc0 or __builtin_mtc0 function.
    C32-347:
      The stack pointer is now always aligned to 8, even with the existence of a .ramfunc section. In earlier compiler releases, a function utilizing the `__longramfunc__` macro could cause the stack pointer to become misaligned. This could then potentially cause stack corruption if the application later called a vararg function and passed a 64-bit wide parameter such as a long double or a long long. The default linker script provided with this release corrects this potential issue.
    C32-353:
      In the v1.11 and v1.11(B) releases, some processor header files contained an SFR union with an empty nested struct. This extraneous empty struct has been removed.

    ## Fixed in v1.11

    C32-318:
      IPLnSOFT interrupts nested in IPLnSRS interrupts now preserve the stack pointer across register sets. Previously, nested interrupts with shadow register set 1 assigned to a lower priority ISR (e.g. IPL1SRS) could cause stack pointer corruption. The most common symptom of stack corruption is a general exception after returning from the ISR. Thanks to A. Chen for reporting this issue via http://support.microchip.com
    C32-314:
      The default general-exception context-saving code now allocates sufficient stack space for the number of general registers that it saves. The previous default code did not allocate sufficient space and resulted in stack corruption following a general exception. This made recovering from a general exception impossible when using the default context-saving code.
    C32-312:
      The compiler no longer generates an extraneous instruction a function epilogue for non-interrupt function where no additional stack space needs to be deallocated. The v1.10 release incorrectly generated a useless `addiu sp,sp,0` instruction. Thanks to Slawek Piotrowski for reporting this issue on the Microchip web forum.
    C32-300:
      The compiler now maintains an 8-byte alignment for the stack pointer for all functions including interrupt service routines. In prior compiler releases, when a function taking a variable number of arguments was called from an interrupt service routine and an 8-byte variable was passed as an argument, the generated code could cause a general exception. Thanks to Leon van Snippenberg of AVIX for reporting this issue.
    C32-298:
      A constant infinite loop within an IPLxAUTO interrupt service routine no longer causes an internal compiler error.
    C32-297:
      The CP0 access macros in cp0defs.h no longer cause an exception when used in a mips16 function. These access macros now use the new CP0 builtin functions described in the New Features in v1.11 section above.
    C32-292:
      The compiler now properly ignores the -mips16 and higher-level optimization options when they are passed together to a compiler operating with a limited-functionality license such as a lite-mode license or an expired standard evaluation license. Previous releases emitted a correct warning followed by an incorrect error.
    BIN32-44:
      The pic32-size utility now reports the size of COMMON section correctly as part of the bss section usage.

    ## Fixed in v1.10

    C32-267:
      The '0' (zero-fill) flag for the output-format conversion specifiers (used with the printf functions), now properly causes zero filling when used with floating-point conversions. (e.g. `printf("%010.2f",foo);` )
    C32-266:
      A 'naked' attributed function containing a function call no longer causes a compiler crash when building with optimizations enabled.
    C32-252:
      The SoftReset() peripheral library function now works correctly on devices that do not use DMA, such as the PIC32MX320F032H.
    C32-224:
      In stdlib.h, MB_CUR_MAX is now correctly defined as 1.
    DAYHLD-10:
      The UPLLIDIV configuration fuse settings were incorrectly named DIV_7 and DIV_8 for several PIC32MX4XX devices. They are now correctly named DIV_10 and DIV_12, respectively.

    ## Fixed in v1.05

    C32-064:
      Code generated using -Os -mips16 and a very large number of common subexpressions now compiles correctly.
    C32-232:
      Interrupt context-saving code now preserves the assembler temporary ($at) register. While the compiler does not use this register for standard C code, the general DSP library or the optimized math library use this register.
    Peripheral Library:
      The peripheral-library source files listed below contain fixes and improvements. See the updated peripheral-library documentation for further details.
      - pic32mx/include/peripheral/int.h
      - pic32mx/include/peripheral/incap.h
      - pic32mx/include/peripheral/nvm.h
      - pic32mx/include/peripheral/dma.h
      - pic32mx/include/peripheral/ports.h
      - pic32mx/include/peripheral/uart.h
      - pic32mx/include/peripheral/i2c.h
      - pic32mx/include/peripheral/outcompare.h
      - pic32mx/include/peripheral/cmp.h
      - pic32mx/include/peripheral/timer.h
      - pic32mx/include/peripheral/reset.h
      - pic32mx/include/peripheral/pcache.h
      - pic32mx/include/peripheral/system.h
      - pic32mx/include/peripheral/bmx.h
      - pic32-libs/peripheral/nvm/source/nvm_operation_lib.c
      - pic32-libs/peripheral/i2c/source/idle_i2c2_lib.c
    C32-42:
      The compiler now emits a more useful diagnostic message when multiple -mprocessor options appear on the command line.

    ## Fixed in v1.04

      No significant fixed issues for this release

    ## Fixed in v1.03

    BIN32-30:
      Assertion statements in the linker scripts now correctly compare the size of an exception vector to the vector spacing.
    C32-179:
      The gmtime() library function now links without error. In previous releases, the linker would complain about an undefined reference to 'offtime_r'
    C32-172:
      The config pragma now defaults the DEVCFG0 MSb to zero.
    C32-171:
      The first call to getchar() now calls _mon_getc(). The previous implementation treated the initial STDIN character as an ungetc() pushed-back character.
    C32-164:
      The device-specific header files now use '__asm__' rather than 'asm' when mapping each SFR struct to it's symbol name. Previous versions of these files did not compile when building with the compiler's -ansi option.
    C32-147:
      The interrupt attribute now properly accepts an uppercase IPLx value. Earlier compiler versions could reject the uppercase IPLx with an internal error.

    ## Fixed in v1.02

    C32-119:
      Removed pipeline interlock in ISR handling
    C32-141:
      Large `malloc()` calls no longer generate a general exception vector instead of returning a NULL pointer.
    C32-144:
      Interrupt macro now sets `nomips16`
    C32-145:
      Include C startup code source is now provided in the standard distribution
    C32-151:
      IPL7 prologue code now sets incorrect bits in status register

11. # Known Issues

    The current known issues are as follows.

    ## Compiler

    C32-345
      The compiler will "terminate in an unusual way" if the Windows TEMP environment variable is set to an invalid directory. You can correct your TEMP environment variable in the Windows Control Panel (Control Panel -> System -> Advanced -> Environment Variables). TEMP should point to an appropriate directory for temporary files.
    C32-463
      The compiler may terminate with an internal error when a mips16 attributed function is inlined in a non-mips16 function or vice versa. This can happen at optimization levels -O2 or -O3. To get around this problem, combine the noinline attribute with your mips16 and/or nomips16 function attribute. The noinline attribute prevents the function from being inlined into another function of a different ISA mode.

    ## Assembler

    BIN32-68
      The assembler may emit an error, 'Macro used $at after".set noat"', for a macro/synthesized instruction even when the synthesized instruction does not use the $at register. A workaround is to replace the macro instruction with the actual instructions.

    ## Linker

    BIN32-58
      The linker may emit an unfriendly error message when it encounters a case where it cannot switch ISA modes between mips16 and mips32 in a function call. The error message is "jump to stub routine which is not jal". This condition can occur when a mips32 function's final statement is a call to a mips16 function and compiler optimizations are enabled.

      Example:
      `extern void bar (void);
      void foo (void);
      void foo (void)
      {
      bar();
      }`
      The file containing `bar()` was compiled with `-mips16` and the file containing `foo()` was compiled with `-O2` but not `-mips16`. This means that the call to `bar()` must change ISA modes. Also, the call to `bar()` is the last statement in the `foo()` function.

      Possible workarounds include

      1. Use the mips16/nomips16 function attribute to make the caller function and the callee function the same ISA mode. Usually, this means applying the `__attribute__((mips16))` or `__attribute__((nomips16))` to the caller function to make it match the callee. This eliminates the need for a mode switch when calling the function.

         The example above becomes:
         `extern void bar (void);
         void __attribute__((mips16)) foo (void);
         void __attribute__((mips16)) foo (void)
         {
         bar();
         }`

      2. If your particular instance of this problem is caused by the tail sibling-call optimization, use the `-fno-optimize-sibling-calls` option when compiling the caller function. In MPLAB IDE v8.xx, you can add this option to your project's alternate settings. This will prevent the compiler converting your 'jal' call into a 'j' branch, which cannot change ISA modes.
      A future release of the linker will emit a more friendly and useful error message.

    ## Libraries and Device-Support Files

    C32-319
      GenericTypeDefs.h defines common data types (such as BYTE, BOOL, UINT16, etc.) that may conflict with definitions in non-Microchip code when using Microchip libraries. When conflicts occur, it will cause compilation errors in the Microchip-provided libraries or in the non-Microchip libraries (depending on which library first defines the data type).

      Possible workaround:
      Remove conflicting definitions from source code.

    C32-479
      When combining the `-fno-short-double` and `-mno-float` compiler options and calling a `scanf()` or related function, the linker may emit an error indicating undefined references to `_dstrtod` and `strtof`. You are not likely to see this issue because combining -fno-short-double, which requests a 64-bit double type, with -mno-float, which disables floating-point support, is not common.

      Possible workaround:
      Remove the either the -fno-short-double or -mno-float option.

    ## Documentation

      ### MPLAB C Compiler for PIC32 MCUs User's Guide (DS1686B)

      Section 5.6 Function Calling Convention - This section states that "The Stack Pointer is always aligned on a 4-byte boundary." This statement is incorrect. The Stack Pointer is always aligned on an 8-byte boundary.

12. # Editions and License Upgrades

    ## Standard Evaluation Edition

    Microchip provides a free Standard Evaluation edition of the MPLAB C Compiler for PIC32 MCUs. The standard evaluation edition of the compiler provides additional functionality for 60 days. After the evaluation period has expired, the compiler becomes reverts to the lite edition, and optimization features associated with levels -O2, -O3, and -Os are disabled. In addition, MIPS16 code generation is disabled. The compiler continues to accept the -O1 and -O0 optimization levels indefinitely.

    Installing the standard evaluation edition - To install the standard evaluation edition of the compiler, run the standard evaluation-edition installer and follow the on-screen instructions. If the installer asks for a license key, leave the field blank and continue.

    Upgrading to a standard-edition license - For applications requiring additional code efficiency, as well as full support via http://www.microchip.com/support, users are encouraged to upgrade to a full standard-edition compiler license. For further information on upgrading to a full standard-edition license (Part Number: SW006015), visit http://www.microchipdirect.com or contact your preferred Microchip distributor.

    Once you've obtained a standard-edition license key, run the Upgrader tool (pic32-upgrader\upgrader.exe) as a Windows administrator. After you enter your license key and press the Upgrade button, the license manager should then report the license upgrade status.

    ## Lite Edition

    Microchip provides a free Lite edition of the MPLAB C Compiler for PIC32 MCUs intended for use in projects where code efficiency is not critical. This edition of the compiler does not support optimization features associated with levels -O2, -O3, and -Os. In addition, this edition does not support MIPS16 code generation.

    Upgrading to the standard edition or standard evaluation edition - To take advantage of the advanced optimization and MIPS16 code generation features, you can upgrade to a standard edition or a 60-day standard evaluation edition. To upgrade to a full or 60-day standard evaluation edition, uninstall the lite edition using the normal Windows Add/Remove Programs feature. Next, install the standard edition or the standard evaluation edition by running the appropriate installer and following the on-screen instructions.

13. # Customer Support

    Microchip provides online support via our home page at:
    http://www.microchip.com

    Technical support is available through the web site at:
    http://www.microchip.com/support

    A forum for discussion of Microchip products and tools is available at:
    http://www.microchip.com/forums

    Microchip PIC32 documentation and product info is available at:
    http://www.microchip.com/pic32

    MPLAB® C Compiler for PIC32 MCUs updates and information are available at:
    http://www.microchip.com/c32