bare-arm: Clean up the code, make it run on an F405, and add a README.

This commit simplifies and cleans up the bare-arm port, and adds just
enough system and library code to make it execute on an STM32F405 MCU.

The mpconfigport.h configuration is simplified to just specify those
configuration values that are different from the defaults.  And the
addition of -fdata-sections and -ffunction-sections means the final
firmware is smaller than it previously was, by about 4200 bytes.

A README is also added.

Signed-off-by: Damien George <damien@micropython.org>

1 files changed, 17 insertions, 76 deletions

diff --git a/ports/bare-arm/stm32f405.ld b/ports/bare-arm/stm32f405.ld
index dd688a024..33a5502d6 100644
--- a/ports/bare-arm/stm32f405.ld
+++ b/ports/bare-arm/stm32f405.ld
@@ -1,117 +1,58 @@
-/*
-    GNU linker script for STM32F405
-*/
+/* GNU linker script for STM32F405 */
 
-/* Specify the memory areas */
 MEMORY
 {
     FLASH (rx)      : ORIGIN = 0x08000000, LENGTH = 0x100000 /* entire flash, 1 MiB */
-    FLASH_ISR (rx)  : ORIGIN = 0x08000000, LENGTH = 0x004000 /* sector 0, 16 KiB */
-    FLASH_TEXT (rx) : ORIGIN = 0x08020000, LENGTH = 0x080000 /* sectors 5,6,7,8, 4*128KiB = 512 KiB (could increase it more) */
-    CCMRAM (xrw)    : ORIGIN = 0x10000000, LENGTH = 0x010000 /* 64 KiB */
     RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 0x020000 /* 128 KiB */
 }
 
-/* top end of the stack */
 _estack = ORIGIN(RAM) + LENGTH(RAM);
 
-/* RAM extents for the garbage collector */
-_ram_end = ORIGIN(RAM) + LENGTH(RAM);
-_heap_end = 0x2001c000; /* tunable */
-
-/* define output sections */
 SECTIONS
 {
-    /* The startup code goes first into FLASH */
     .isr_vector :
     {
         . = ALIGN(4);
-        KEEP(*(.isr_vector)) /* Startup code */
-
+        KEEP(*(.isr_vector))
         . = ALIGN(4);
-    } >FLASH_ISR
+    } >FLASH
 
-    /* The program code and other data goes into FLASH */
     .text :
     {
         . = ALIGN(4);
-        *(.text)           /* .text sections (code) */
-        *(.text*)          /* .text* sections (code) */
-        *(.rodata)         /* .rodata sections (constants, strings, etc.) */
-        *(.rodata*)        /* .rodata* sections (constants, strings, etc.) */
-    /*  *(.glue_7)   */    /* glue arm to thumb code */
-    /*  *(.glue_7t)  */    /* glue thumb to arm code */
-
+        *(.text)
+        *(.text*)
+        *(.rodata)
+        *(.rodata*)
         . = ALIGN(4);
-        _etext = .;        /* define a global symbol at end of code */
-        _sidata = _etext;  /* This is used by the startup in order to initialize the .data secion */
-    } >FLASH_TEXT
-
-    /*
-    .ARM.extab :
-    {
-        *(.ARM.extab* .gnu.linkonce.armextab.*)
+        _etext = .;
+        _sidata = _etext;
     } >FLASH
 
-    .ARM :
-    {
-        __exidx_start = .;
-        *(.ARM.exidx*)
-        __exidx_end = .;
-    } >FLASH
-    */
-
-    /* This is the initialized data section
-    The program executes knowing that the data is in the RAM
-    but the loader puts the initial values in the FLASH (inidata).
-    It is one task of the startup to copy the initial values from FLASH to RAM. */
     .data : AT ( _sidata )
     {
         . = ALIGN(4);
-        _sdata = .;        /* create a global symbol at data start; used by startup code in order to initialise the .data section in RAM */
-        _ram_start = .;    /* create a global symbol at ram start for garbage collector */
-        *(.data)           /* .data sections */
-        *(.data*)          /* .data* sections */
-
+        _sdata = .;
+        *(.data)
+        *(.data*)
         . = ALIGN(4);
-        _edata = .;        /* define a global symbol at data end; used by startup code in order to initialise the .data section in RAM */
+        _edata = .;
     } >RAM
 
-    /* Uninitialized data section */
     .bss :
     {
         . = ALIGN(4);
-        _sbss = .;         /* define a global symbol at bss start; used by startup code */
+        _sbss = .;
         *(.bss)
         *(.bss*)
         *(COMMON)
-
         . = ALIGN(4);
-        _ebss = .;         /* define a global symbol at bss end; used by startup code */
+        _ebss = .;
     } >RAM
 
-    /* this is to define the start of the heap, and make sure we have a minimum size */
     .heap :
     {
-        . = ALIGN(4);
-        _heap_start = .;    /* define a global symbol at heap start */
+        . = ALIGN(8);
+        _heap_start = .;
     } >RAM
-
-    /* this just checks there is enough RAM for the stack */
-    .stack :
-    {
-        . = ALIGN(4);
-    } >RAM
-
-    /* Remove information from the standard libraries */
-    /*
-    /DISCARD/ :
-    {
-        libc.a ( * )
-        libm.a ( * )
-        libgcc.a ( * )
-    }
-    */
-
-    .ARM.attributes 0 : { *(.ARM.attributes) }
 }