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[Cortex-M3] Execution code from RAM during Flash Programming

I am writing a bootloader for Cortex M3 Toshiba controller.

During Flash Programming I need to execute code from RAM as entire Flash is inaccessible during write/erase operations

I wish to know how to copy code from FLASH to RAM and execute that code from RAM.

Thanks...

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Joseph Yiu over 10 years ago

Note: This was originally posted on 14th March 2012 at http://forums.arm.com

In that case, it would be easier to copy the whole boot loader (rather than a portion of it) from flash to SRAM in the assembly startup code.
The boot loader, assumed to be mostly written in C, will have to linked to use the SRAM address as program memory range.

In the assembly startup code you will have a reset handler, and normally you can see something like:

Reset_Handler   PROC
             EXPORT Reset_Handler    [WEAK]
             IMPORT __main
             LDR R0,=__main
             BX     R0   ; this branch to C startup code
             ENDP

You can insert an assembly code to copy the memory from flash to SRAM, before jumping to the C startup code which will be in SRAM.

Reset_Handler   PROC
             EXPORT Reset_Handler    [WEAK]
             LDR R4,=0x00000000 ; Source starting address
             LDR R5,=0x20000000 ; Destination starting address
             LDR R6,=0x4000 ; 16K program size to copy
CopyFlashToSRAMLoop
             LDMIA R4!,{R0-R3}
             STMIA R5!,{R0-R3}
             LDMIA R4!,{R0-R3}
             STMIA R5!,{R0-R3}
             LDMIA R4!,{R0-R3}
             STMIA R5!,{R0-R3}
             LDMIA R4!,{R0-R3}
             STMIA R5!,{R0-R3}
             SUBS R6,#64 ; Each time 64 bytes are copied
             BNE CopyFlashToSRAMLoop
             IMPORT __main
             LDR R0,=__main
             BX     R0   ; this branch to C startup code
             ENDP

In this way, the whole boot loader will be running in SRAM. You need to be careful to make sure that the data use by the boot loader is not in the same address as the instruction memory.

regards,
Joseph
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Joseph Yiu over 10 years ago

Note: This was originally posted on 14th March 2012 at http://forums.arm.com

In that case, it would be easier to copy the whole boot loader (rather than a portion of it) from flash to SRAM in the assembly startup code.
The boot loader, assumed to be mostly written in C, will have to linked to use the SRAM address as program memory range.

In the assembly startup code you will have a reset handler, and normally you can see something like:

Reset_Handler   PROC
             EXPORT Reset_Handler    [WEAK]
             IMPORT __main
             LDR R0,=__main
             BX     R0   ; this branch to C startup code
             ENDP

You can insert an assembly code to copy the memory from flash to SRAM, before jumping to the C startup code which will be in SRAM.

Reset_Handler   PROC
             EXPORT Reset_Handler    [WEAK]
             LDR R4,=0x00000000 ; Source starting address
             LDR R5,=0x20000000 ; Destination starting address
             LDR R6,=0x4000 ; 16K program size to copy
CopyFlashToSRAMLoop
             LDMIA R4!,{R0-R3}
             STMIA R5!,{R0-R3}
             LDMIA R4!,{R0-R3}
             STMIA R5!,{R0-R3}
             LDMIA R4!,{R0-R3}
             STMIA R5!,{R0-R3}
             LDMIA R4!,{R0-R3}
             STMIA R5!,{R0-R3}
             SUBS R6,#64 ; Each time 64 bytes are copied
             BNE CopyFlashToSRAMLoop
             IMPORT __main
             LDR R0,=__main
             BX     R0   ; this branch to C startup code
             ENDP

In this way, the whole boot loader will be running in SRAM. You need to be careful to make sure that the data use by the boot loader is not in the same address as the instruction memory.

regards,
Joseph
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