SLAU646F September   2015  – June 2020

 

  1.   Read This First
    1.     How to Use This User's Guide
    2.     Related Documentation
    3.     If You Need Assistance
    4.     Trademarks
  2. 1Introduction
  3. 2Installing MSP430 GCC Toolchain
    1. 2.1 Installing MSP430 GCC in CCS Releases Before v7.2
    2. 2.2 Installing MSP430 GCC as Stand-Alone Package
  4. 3Using MSP430 GCC Within CCS
    1. 3.1 Create New Project
    2. 3.2 Debug Using MSP-FET, MSPFET430UIF, eZ-FET, eZ430
    3. 3.3 Build Options for MSP430 GCC
      1. 3.3.1  GNU Compiler
      2. 3.3.2  GNU Compiler: Runtime
      3. 3.3.3  GNU Compiler: Symbols
      4. 3.3.4  GNU Compiler: Directories
      5. 3.3.5  GNU Compiler: Optimization
      6. 3.3.6  GNU Compiler: Preprocessor
      7. 3.3.7  GNU Compiler: Assembler
      8. 3.3.8  GNU Compiler: Debugging
      9. 3.3.9  GNU Compiler: Diagnostic Options
      10. 3.3.10 GNU Compiler: Miscellaneous
      11. 3.3.11 GNU Linker
      12. 3.3.12 GNU Linker: Basic
      13. 3.3.13 GNU Linker: Libraries
      14. 3.3.14 GNU Linker: Symbols
      15. 3.3.15 GNU Linker: Miscellaneous
      16. 3.3.16 GNU Objcopy Utility
    4. 3.4 CCS Compared to MSP430 GCC
  5. 4MSP430 GCC Stand-Alone Package
    1. 4.1 MSP430 GCC Stand-Alone Package Folder Structure
    2. 4.2 Package Content
    3. 4.3 MSP430 GCC Options
    4. 4.4 MSP430 Built-in Functions
    5. 4.5 Using MSP430 GCC Support Files
    6. 4.6 Quick Start: Blink the LED
      1. 4.6.1 Building with a Makefile
      2. 4.6.2 Building Manually with gcc
      3. 4.6.3 Debugging
        1. 4.6.3.1 Starting GDB Agent
          1. 4.6.3.1.1 Using the GUI
          2. 4.6.3.1.2 Using the Command Line
        2. 4.6.3.2 Debugging With GDB
          1. 4.6.3.2.1 Running a Program in the Debugger
          2. 4.6.3.2.2 Setting a Breakpoint
          3. 4.6.3.2.3 Single Stepping
          4. 4.6.3.2.4 Stopping or Interrupting a Running Program
      4. 4.6.4 Creating a New Project
    7. 4.7 GDB Settings
      1. 4.7.1 Console Application
      2. 4.7.2 Optional Parameters for msp430.dat
      3. 4.7.3 GUI Application
      4. 4.7.4 Attaching the Debugger
      5. 4.7.5 Configuring the Target Voltage
      6. 4.7.6 Resetting the Target
      7. 4.7.7 Halting the Target
  6. 5MSP430 GCC Features
    1. 5.1 C/C++ Attributes
      1. 5.1.1 GCC Function Attribute Support
      2. 5.1.2 GCC Data Attribute Support
      3. 5.1.3 GCC Section Attribute Support
    2. 5.2 Hints for Reducing the Size of MSP430 GCC Programs
      1. 5.2.1 The -mtiny-printf Option
      2. 5.2.2 The -ffunction-sections and -fdata-sections Options
      3. 5.2.3 Making Large Programs Fit Across Upper and Lower Memory
      4. 5.2.4 NOP Instructions Surrounding Interrupt State Changes
    3. 5.3 C Runtime Library (CRT) Startup Behavior
    4. 5.4 Using printf with MSP430 GCC
    5. 5.5 Link-time Optimization (LTO)
    6. 5.6 The __int20 Type and Pointers in the Large Memory Model
  7. 6Building MSP430 GCC From Sources
    1. 6.1 Required Tools
    2. 6.2 Building MSP430 GCC (Mitto Systems Limited)
      1. 6.2.1 Building a Native MSP430 GCC Toolchain
      2. 6.2.2 Building the MSP430 GCC Toolchain for Windows
    3. 6.3 Building MSP430 GCC Stand-Alone Full Package
  8. 7MSP430 GCC and MSPGCC
    1. 7.1 Calling Convention
    2. 7.2 Other Portions of the ABI
  9. 8Appendix
    1. 8.1 GCC Intrinsic Support
    2. 8.2 NOP Instructions Required Between Interrupt State Changes
  10. 9References
  11.   Revision History

7.1 Calling Convention

For developers writing assembly code, the most noticeable part of an ABI is the calling convention. Full specification of the calling convention is very detailed (see MSP430 Embedded Application Binary Interface), but developers writing assembly do not typically use most of it. There are three basic differences between MSPGCC and the GCC compiler for MSP in the calling convention that are important to be aware of:

  • In MSPGCC, registers are passed starting with R15 and descending to R12. For example, if two integers are passed, the first is passed in R15 and the second is passed in R14. In contrast, the MSP430 EABI specifies that arguments are passed beginning with R12 and moving up to R15. So, in the same situation, registers R12 and R13 would hold the two arguments. In both cases, after the registers R12 through R15 are used, continued arguments are passed on the stack. If you are using stack-based arguments, you should consult the EABI specification.
  • MSPGCC and the GCC compiler for MSP use different registers for the return value. MSPGCC places the return value in R15 (or R15 and consecutive lower registers if the value is larger than a word), while the EABI specifies that the return value is placed in R12.
  • In MSPGCC, register R11 is considered a save on entry register and needs to be saved and restored by the callee if it is used in the called function. Conversely, the MSP EABI specifies that R11 is a save on call register, so it needs to be saved and restored by the calling function if its value will be needed after a function call. For comparison purposes, R4 to R10 are save on entry registers for both compilers, and R12 to R15 are save on call.

These are the key differences to be aware of when moving between the compilers. If you are writing assembly code that passes parameters on the stack or that passes structures by value, you should consult the MSP EABI document for additional information.