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Jump to application at 0x8001000 when no bootloader is present

Tom
Associate II

Hi Guys,

I'm writting a bootlader/application for STM32L4 in STM32CubeIDE i I want my app to run even if there is no bootloader in memory.

This is my *.ld file:

/* Memories definition */
MEMORY
{
  RAM    (xrw)    : ORIGIN = 0x20000000,   LENGTH = 96K
  RAM2    (xrw)    : ORIGIN = 0x10000000,   LENGTH = 32K
  FLASH    (rx)    : ORIGIN = 0x8001000,   LENGTH = 1024K-0x1000
  BOOT     (rx)    : ORIGIN = 0x8000000,   LENGTH = 131K
}

I my app source I have the below function (which is properly placed at 0x8000000 in flash) :

#define MY_BL_FUNCTIONS __attribute__((section(".bootsection")))
void __attribute__((optimize("O0"))) Bootloader_JumpToApplication(void); MY_BL_FUNCTIONS
 
void __attribute__((optimize("O0"))) Bootloader_JumpToApplication(void)
{
        asm("ldr R0,=0x8001004"); //my app start address
        asm("BX R0");   //jump to app
}

Unfortunately asm("BX R0") makes a sudden jump to my HardFault_Handler. instead of 0x8001004.

What do I do wrong?

Thanks in advance

Tom

8 REPLIES 8
Bassett.David
Associate III

Hello Tom,

Perhaps try "asm("ldr R0,=0x8001005"); //my app start address"

I believe Thumb-2 addresses are designated by bit-0 set.

Good Luck,

Dave

Show disasm.

> function (which is properly placed at 0x8000000 in flash)

A minimal vector table has to be at 0x0800'0000, with address of that function (possibly 0x0800'0009, if it follows immediately after that vector table) at 0x0800'0004.

[EDIT] Oh, and the displacement may be too far to use the pc-relative addressing (to which ldr R0, =xxxx translates)

 https://developer.arm.com/documentation/dui0552/a/the-cortex-m3-instruction-set/memory-access-instructions/ldr--pc-relative

JW

No, doesn't work like that.

Also Vector Table, is a TABLE OF ADDRESSES, NOT CODE, Thumb code has an ODD address, the Cortex-M can't execute 32-bit ARM code, with EVEN addresses.

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Tom
Associate II

Thanks guys, I changed my bootloader func. to:

    SCB->VTOR=0x8001000;
    asm("ldr R0,=0x8001004");
    asm("BX R0");

tried asm("ldr R0,=0x8001005"); too but same result.

Of course I also did in system_stm32l4xx.c:

#define VECT_TAB_OFFSET    0x1000

This is my disassembly:

08000000:   push    {r7}
08000002:   add     r7, sp, #0
08000004:   ldr     r3, [pc, #16]   ; (0x8000018 <Bootloader_JumpToApplication+24>)
08000006:   ldr     r2, [pc, #20]   ; (0x800001c <Bootloader_JumpToApplication+28>)
08000008:   str     r2, [r3, #8]
0800000a:   ldr     r0, [pc, #20]   ; (0x8000020)
0800000c:   bx      r0
0800000e:   nop     
08000010:   mov     sp, r7
08000012:   ldr.w   r7, [sp], #4
08000016:   bx      lr
08000018:   stc     0, cr14, [r0, #-0]
0800001c:   asrs    r0, r0, #32
0800001e:   lsrs    r0, r0, #32
08000020:   asrs    r4, r0, #32
08000022:   lsrs    r0, r0, #32
08000024:           ; <UNDEFINED> instruction: 0xffffffff
08000028:           ; <UNDEFINED> instruction: 0xffffffff
0800002c:           ; <UNDEFINED> instruction: 0xffffffff
08000030:           ; <UNDEFINED> instruction: 0xffffffff
08000034:           ; <UNDEFINED> instruction: 0xffffffff

Tom

LDR Rx,= will translate to an ADD/SUB (near or further) with PC for short compatible addresses, an immediate move if the constant packs, or a PC relative load access to a literal pool.

What you can't do is branches to the entire 32-bit address space

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VECTOR TABLE != CODE

What are words at 0x08000000 and 0x08001000 should be initial SP/PC pair at minimum

Execution starts assuming SCB->VTOR = 0, memory mapped at zero depends on BOOT pins, and can be ROM, FLASH or RAM

ldr r0,=0x08001004

ldr r0,[r0, #0] ; Load ADDRESS in VTOR+4

bx r0

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Piranha
Chief II

Apart from the official documentation by ARM and ST, the internet is full of materials about Cortex-M vector table, startup scripts etc.

  FLASH    (rx)    : ORIGIN = 0x8001000,   LENGTH = 1024K-0x1000
  BOOT     (rx)    : ORIGIN = 0x8000000,   LENGTH = 131K

0x1000 = 4K. Those regions have an overlap of a 127K!

> I want my app to run even if there is no bootloader in memory.

You are misunderstanding what a bootloader is. Bootloader is a code that is always present and always capable of recovering a device to a fully working condition. If there is some boot/update code that can be missing or otherwise broken at some point, then that is a second (stage) bootloader.

Tom
Associate II

Hi Piranha

The overlap is no the problem here, as everything goes into flash as expected as you could see.

I understand how bootloader works but at dev stage in order to flash bootloader and app I'd have to manuallly merge bootloader hex and app hex before programming which I dont want cause it makes no sense. It is easier to place a simple jump at 0x8000000 to the app so I can quickly debug and run the app in CubeIDE.