I'm working on a custom boot loader for a STM32F429, where I want to reserve the second of the first four 16K flash sectors for user data. Because the vector table has to start at 0x08000000, the memory layout would look like this:
0x08000000 - isr vector table and padding (16K)
0x08004000 - user flash sector (16K)
0x08008000 - bootloader code (224K)
------------------
0x0800C000 - application code with footer containing version and CRC (768K)
This gives me a size constraint of 256K for the boot loader code. That's why I want to use the second flash sector, because this is one of the 16K ones. Nice and small, leaving enough room for the code.
I'm using a modified version of ST's original gnu linker script:
/* Custom bootloader linker script, edited from ST's STM32F429IITx_FLASH.ld. */
/* Entry Point */
ENTRY(Reset_Handler)
/* Highest address of the user mode stack */
_estack = 0x20030000; /* end of RAM */
/* Generate a link error if heap and stack don't fit into RAM */
_Min_Heap_Size = 0x200; /* required amount of heap */
_Min_Stack_Size = 0x400; /* required amount of stack */
/* Specify the memory areas */
MEMORY
{
ISR_VECTOR (rx) : ORIGIN = 0x08000000, LENGTH = 16K /* isr_vector in first 16K sector */
USER_FLASH (rx) : ORIGIN = 0x80004000, LENGTH = 16K /* attempt to put user flash in second 16K sector */
FLASH (rx) : ORIGIN = 0x08008000, LENGTH = 224K /* "regular" flash starts from the 3rd sector.Total is 256K maximum.*/
CCMRAM (rw) : ORIGIN = 0x10000000, LENGTH = 64K
RAM (xrw) : ORIGIN = 0x20000000, LENGTH = 191K /* deduct 1K for NOINIT data */
NOINIT (rwx) : ORIGIN = 0x2002FC00, LENGTH = 1K /* NOINIT data will survive reset */
}
/* Define output sections */
SECTIONS
{
/* The startup code goes first into FLASH */
.isr_vector :
{
. = ALIGN(4);
KEEP(*(.isr_vector)) /* Vector table */
. = ALIGN(4);
} >ISR_VECTOR
/* Then comes user flash sector, make sure to get one of the first 4 that are 16K in size */
.user_flash :
{
. = ALIGN(4);
KEEP(*(.user_flash))
. = ALIGN(4);
} >USER_FLASH
/* The program code and other data goes into FLASH */
.text :
{
. = ALIGN(4);
*(.text) /* .text sections (code) */
*(.text*) /* .text* sections (code) */
*(.glue_7) /* glue arm to thumb code */
*(.glue_7t) /* glue thumb to arm code */
*(.eh_frame)
KEEP (*(.init))
KEEP (*(.fini))
. = ALIGN(4);
_etext = .; /* define a global symbols at end of code */
} >FLASH
/* ...rest of sections ommitted here. */
In my "user_flash.c" file I declare the user data like this:
__attribute__((__section__(".user_flash"))) const uint32_t user_flash[0x4000 / sizeof(uint32_t)] = {0};
To list where all the sections end up after linking I run:
"arm-none-eabi-objdump -h Bootloader-V0.6"
I then get the following output:
Bootloader-V0.6: file format elf32-littlearm
Sections:
Idx Name Size VMA LMA File off Algn
0 .isr_vector 000001ac 08000000 08000000 00010000 2**0
CONTENTS, ALLOC, LOAD, READONLY, DATA
1 .text 00019b28 08008000 08008000 00018000 2**6
CONTENTS, ALLOC, LOAD, READONLY, CODE
2 .rodata 000017e8 08021b28 08021b28 00031b28 2**3
CONTENTS, ALLOC, LOAD, READONLY, DATA
3 .user_flash 00004000 08023310 08023310 00033310 2**2
CONTENTS, ALLOC, LOAD, READONLY, DATA
4 .ARM.extab 00000308 08027310 08027310 00037310 2**2
CONTENTS, ALLOC, LOAD, READONLY, DATA
5 .ARM 00000360 08027618 08027618 00037618 2**2
#rest of output omitted
No matter what I try, I can't seem to fit ".user_flash" in between ".isr_vector" and ".text", even though I specify this in the linker script.
I've also tried to put everything in the FLASH memory region by specifying ".user_flash" like this:
.user_flash :
{
. = ALIGN(0x4000);
KEEP(*(.user_flash))
. = ALIGN(4);
} >FLASH
and
.user_flash :
{
. = 0x08004000
KEEP(*(.user_flash))
. = ALIGN(4);
} >FLASH
to no avail. I don't understand what's I'm doing wrong here. Perhaps a linker bug?
I could try to get ".user_flash" placed at the end of the boot loader binary, but then It will use a 128K sector and severely limit my boot loader code size: I really need the 16K one for that.
