Difference between revisions of "Minimal semihosted ARM Cortex-M "Hello World""

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The following is an extremely minimal, semihosted "Hello World" D program for ARM Cortex-M processors.
+
The following is a minimal, semihosted "Hello World" D program for ARM Cortex-M processors.
  
 
=Goals=   
 
=Goals=   
Line 10: Line 10:
 
=Tools=
 
=Tools=
 
* (host computer) [https://www.archlinux.org/ Arch Linux] 64-bit
 
* (host computer) [https://www.archlinux.org/ Arch Linux] 64-bit
* (compiler) [http://wiki.dlang.org/LDC LDC] with ARM backend
+
* (compiler) [http://wiki.dlang.org/LDC LDC] with ARM backend, or [http://wiki.dlang.org/GDC/Cross_Compiler GDC cross-compiler] for arm-none-eabi 4.9.2
* (linker & debugger) GNU Tools for [https://launchpad.net/gcc-arm-embedded GNU Tools for ARM Embedded Processors] 4.7-2013-q3
+
* (GDB client) GNU Tools for [https://launchpad.net/gcc-arm-embedded GNU Tools for ARM Embedded Processors]
* (GDB server) [http://openocd.sourceforge.net/ OpenOCD] 0.7.0
+
* (GDB server) [http://openocd.sourceforge.net/ OpenOCD] 0.9.0
* (JTAG emulator) [http://www.distortec.com/jtag-lock-pick-tiny-2 JTAG-lock-pick Tiny 2]
+
* ([http://en.wikipedia.org/wiki/In-circuit_emulator In Circuit Emulator]) STLink v2 on [http://www.st.com/web/catalog/tools/FM116/SC959/SS1532/PF259090 STM32F429I-DISCO board]
  
 
=The Code=
 
=The Code=
Line 24: Line 24:
 
   import ldc.llvmasm;
 
   import ldc.llvmasm;
 
}
 
}
 
extern(C) __gshared void * _Dmodule_ref;
 
 
   
 
   
 
//Must be stored as second 32-bit word in .text section
 
//Must be stored as second 32-bit word in .text section
Line 53: Line 51:
 
:                               
 
:                               
 
: [cmd] "r" command, [msg] "r" message
 
: [cmd] "r" command, [msg] "r" message
: "r0", "r1";
+
: "r0", "r1", "memory";
     };
+
     }
 
   }
 
   }
 
}
 
}
Line 62: Line 60:
 
   while(true)
 
   while(true)
 
   {
 
   {
     // Create semihosting message message
+
     // Create semihosting message
 
     uint[3] message =
 
     uint[3] message =
 
       [
 
       [
Line 77: Line 75:
  
 
==Minimal Runtime Implementation (object.d) (GDC only)==
 
==Minimal Runtime Implementation (object.d) (GDC only)==
GDC requires the following minimal object.d file in the same folder as start.d.  It is imported automatically.
+
GDC requires the following minimal object.d file in compiler's import path, which by default is the compiler's working directory.  If compiling from within folder that contains start.d, simply add object.d to that folder.  It is imported automatically.
 
<syntaxhighlight lang="D">
 
<syntaxhighlight lang="D">
 
module object;
 
module object;
 +
</syntaxhighlight >
  
alias immutable(char)[]  string;
+
=Compiling=
</syntaxhighlight >
+
NOTE: You will have to change the -mcpu option for your processor accordingly (e.g. cortex-m0, cortex-m3, etc...)
  
For LDC compile with:
+
===LDC===
 
<source lang="html4strict">
 
<source lang="html4strict">
ldc2 -march=thumb -mcpu=cortex-m4 -c start.d
+
ldc2 -mtriple=thumb-none-linux-eabi -mcpu=cortex-m4 -c -betterC start.d
 
</source>
 
</source>
 +
For LDC, object.d must NOT exist, or it will try to import it automatically.
  
For GDC compile with:
+
===GDC===
 
<source lang="html4strict">
 
<source lang="html4strict">
 
arm-none-eabi-gdc -mthumb -mcpu=cortex-m4 -fno-emit-moduleinfo -c -fdata-sections start.d  
 
arm-none-eabi-gdc -mthumb -mcpu=cortex-m4 -fno-emit-moduleinfo -c -fdata-sections start.d  
 
</source>
 
</source>
You will have to change the -mcpu option for your processor accordingly (e.g. cortex-m0, cortex-m3, etc...)
+
For GDC, object.d MUST exist in the compiler's import path, and it is imported automatically.
  
==Linker Script (link.ld) (LDC)==
+
=Linking=
NOTE: This linker script was written specifically for an STM32F4 MCU.  The ''MEMORY'' section and ''_stackStart'' will have to be tailored to your hardware.
+
NOTE: This linker scripts were written specifically for an STM32F4 MCU.  The ''MEMORY'' section and ''_stackStart'' will have to be tailored to your hardware.
 +
==Linker Script (link.ld) ==
 
<source lang="html4strict">
 
<source lang="html4strict">
 
MEMORY
 
MEMORY
Line 108: Line 109:
  
 
SECTIONS
 
SECTIONS
{
+
{
   .text :
+
   /* We don't need exceptions, and discarding these sections
 +
    prevents linker errors with LDC */
 +
  /DISCARD/ :
 
   {
 
   {
    LONG(_stackStart);              /* Initial stack pointer */
+
     *(.ARM.extab*)
    KEEP(start.o(.data.rel.ro))    /* Interrupt vector table */
+
     *(.ARM.exidx*)
 
+
   }
    /* the code */
 
     *(.text)
 
    *(.text*)
 
 
 
    /* for "hello\r\n" string constant */
 
    . = ALIGN(4);
 
     *(.rodata)
 
    *(.rodata*)
 
   }>FLASH
 
  
  /* Need .data, .bss, .ctors and probably more as program becomes
 
    More complex */
 
}
 
</source>
 
 
Link with:
 
<source lang="html4strict">
 
arm-none-eabi-ld -T link.ld --gc-sections start.o -o start.elf
 
</source>
 
 
==Linker Script (link.ld) (GDC) ==
 
NOTE: This linker script was written specifically for an STM32F4 MCU.  The ''MEMORY'' section and ''_stackStart'' will have to be tailored to your hardware.
 
<source lang="html4strict">
 
/*********************************************************************************************
 
Memory Spaces Definitions
 
*********************************************************************************************/
 
MEMORY
 
{
 
  CCRAM    (rxw) : ORIGIN = 0x10000000, LENGTH =  64k
 
  SRAM    (rxw) : ORIGIN = 0x20000000, LENGTH =  128k
 
  FLASH    (rx)  : ORIGIN = 0x08000000, LENGTH = 1024k
 
}
 
 
_stackStart = ORIGIN(CCRAM) + LENGTH(CCRAM);
 
 
/*********************************************************************************************
 
Section Definitions
 
*********************************************************************************************/
 
SECTIONS
 
 
 
   .text :       
 
   .text :       
 
   {
 
   {
     LONG(_stackStart);                   /* Initial stack pointer */
+
     LONG(_stackStart);             /* Initial stack pointer */
     KEEP(start.o(.rodata.ResetHandler))  /* Internet vector table */
+
     KEEP(start.o(*.ResetHandler))  /* Interrupt vector table (Entry point) */
 
      
 
      
 
     /* the code */
 
     /* the code */
Line 184: Line 148:
 
Start OpenOCD:
 
Start OpenOCD:
 
<source lang="html4strict">
 
<source lang="html4strict">
openocd -f interface/jtag-lock-pick_tiny_2.cfg -f target/stm32f4x.cfg
+
openocd -f board/stm32f429discovery.cfg
 
</source>
 
</source>
  
Line 209: Line 173:
 
</source>
 
</source>
  
=TODO=
+
[[Category:ARM]]
* Modify this software to compile for both GDC and LDC
 
* Modify software to include ''data'' and ''bss'' sections and initialize them in the reset handler (Part 2?)
 
* Begin porting the D Runtime to the ARM Cortex-M platform
 
 
 
[[Category:LDC]]
 

Latest revision as of 15:06, 18 December 2017

The following is a minimal, semihosted "Hello World" D program for ARM Cortex-M processors.

Goals

  • Verify the ARM Cortex-M toolchain (compiler-->linker-->debugger)
  • Demonstrate that a full port of the D runtime and D standard library are not mandatory
  • Demonstrate that linking to C code is not necessary
  • Demonstrate that all required assembly code can be done within D
  • Provide a starting point, with a low barrier to entry, for developers to begin testing the toolchain, porting the D runtime and libraries to the ARM Cortex-M platform, and programming their ARM Cortex-M software in D

Tools

The Code

Program Source Code (start.d)

module start;
 
version(LDC)
{
  import ldc.llvmasm;
}
 
//Must be stored as second 32-bit word in .text section
alias void function() ISR;
extern(C) immutable ISR ResetHandler = &OnReset;
 
void SendCommand(int command, void* message)
{
  version(LDC)
  {
    __asm
    (
      "mov r0, $0;
      mov r1, $1;
      bkpt #0xAB",
      "r,r,~{r0},~{r1}",
      command, message
    );
  }
  else version(GNU)
  {
    asm
    {
      "mov r0, %[cmd]; 
       mov r1, %[msg]; 
       bkpt #0xAB"
	:                              
	: [cmd] "r" command, [msg] "r" message
	: "r0", "r1", "memory";
    }
  }
}
 
void OnReset()
{
  while(true)
  {
    // Create semihosting message
    uint[3] message =
      [
	2, 			      //stderr
	cast(uint)"hello\r\n".ptr,    //ptr to string
	7                             //size of string
      ];

    //Send semihosting command
    SendCommand(0x05, &message);
  }
}

Minimal Runtime Implementation (object.d) (GDC only)

GDC requires the following minimal object.d file in compiler's import path, which by default is the compiler's working directory. If compiling from within folder that contains start.d, simply add object.d to that folder. It is imported automatically.

module object;

Compiling

NOTE: You will have to change the -mcpu option for your processor accordingly (e.g. cortex-m0, cortex-m3, etc...)

LDC

ldc2 -mtriple=thumb-none-linux-eabi -mcpu=cortex-m4 -c -betterC start.d

For LDC, object.d must NOT exist, or it will try to import it automatically.

GDC

arm-none-eabi-gdc -mthumb -mcpu=cortex-m4 -fno-emit-moduleinfo -c -fdata-sections start.d

For GDC, object.d MUST exist in the compiler's import path, and it is imported automatically.

Linking

NOTE: This linker scripts were written specifically for an STM32F4 MCU. The MEMORY section and _stackStart will have to be tailored to your hardware.

Linker Script (link.ld)

MEMORY
{
  CCRAM    (rxw) : ORIGIN = 0x10000000, LENGTH =   64k
  SRAM     (rxw) : ORIGIN = 0x20000000, LENGTH =  128k
  FLASH    (rx)  : ORIGIN = 0x08000000, LENGTH = 1024k
}

_stackStart = ORIGIN(CCRAM) + LENGTH(CCRAM);

SECTIONS
{  
  /* We don't need exceptions, and discarding these sections
     prevents linker errors with LDC */
  /DISCARD/ :
  {
    *(.ARM.extab*)
    *(.ARM.exidx*)
  }

  .text :       
  {
    LONG(_stackStart);              /* Initial stack pointer */
    KEEP(start.o(*.ResetHandler))   /* Interrupt vector table (Entry point) */
    
    /* the code */
    *(.text)      
    *(.text*)  
    
    /* for "hello\r\n" string constant */
    . = ALIGN(4);
    *(.rodata)
    *(.rodata*)
    
  }>FLASH
  
  
  /* Need .data, .bss, .ctors and probably more as program becomes
     More complex */
}

Link with:

arm-none-eabi-ld -T link.ld --gc-sections start.o -o start.elf

Execution

Start OpenOCD:

openocd -f board/stm32f429discovery.cfg

Start GDB:

arm-none-eabi-gdb start.elf

In GDB, attach to OpenOCD, reset the hardware, load the executable, and begin execution

target remote localhost:3333
monitor arm semihosting enable
monitor reset halt
load
monitor reset init
continue

Output (in OpenOCD window):

hello
hello
...