Re: Can the RESET_VECTOR be redefined at compile time to a specific value?

You may be able to use the same approach TinyOS does, using some linker flags. An example for an msp430f1611:

CFLAGS += -Wl,--section-start=.text=0x4a00,--defsym=_reset_vector__=0x4000

So when compiling/linking the application, it moves the text segment up and defines the _reset_vector__ to point at the bootloader. You don't even need a separate linker script.

However, redefining __reset_vector_ apparently makes the compiler discard some symbols referenced from it, which are then manually added back in. The full sequence is:

CFLAGS += -Wl,--section-start=.text=0x4a00,--defsym=_reset_vector__=0x4000
# Pull back in mspgcc CRT code discarded by the redefinition of _reset_vector__
CFLAGS += -Wl,--undefined=__init_stack
CFLAGS += -Wl,--undefined=__low_level_init
CFLAGS += -Wl,--undefined=__do_copy_data
CFLAGS += -Wl,--undefined=__do_clear_bss
CFLAGS += -Wl,--undefined=__stop_progExec__
CFLAGS += -Wl,--undefined=_endless_loop__

HTH,
Michiel

> -----Original Message-----
> From: Tomek Lorek [mailto:[email protected]]
> Sent: Friday, April 18, 2014 19:09
> To: [email protected]
> Subject: [Mspgcc-users] Can the RESET_VECTOR be redefined at compile
> time to a specific value?
> 
> Hi,
> My use case is the following: I have a bootloader (up to 4K in size,
> residing at 0x4400 to 0x5400) that has a main() function and
> application (starting from 0x4800) – they are organized as 2 separate
> projects (I want the bootloader to be flashed only once and not
> changed later).
> 
> I am using mspgcc.
> 
> Bootloader and application linker scripts are defined so that their
> .text sections (that go to “rom” memory region) are separated but they
> use the same “vector” memory region for .vector section (although the
> bootloader does not use any interrupts other than reset):
> 
> bootloader’s linker script excerpt:
> MEMORY {
>   …
>   rom (rx)         : ORIGIN = 0x4400, LENGTH = 0x1000 /* END=0x5400,
> size 4K - bootloader code */
>   rom_app (rx)     : ORIGIN = 0x5400, LENGTH = 0xab80 /* END=0xff80,
> size 43904 - the field-updatable application */
>   vectors          : ORIGIN = 0xff80, LENGTH = 0x0080 /* END=0x10000,
> size 128 as 64 2-byte segments */
>   …
> }
> 
> and the application’s linker script excerpt:
> 
> MEMORY {
>   …
>   rom (rx)         : ORIGIN = 0x5400, LENGTH = 0xab80 /* END=0xff80,
> size 43904 */
>   vectors          : ORIGIN = 0xff80, LENGTH = 0x0080 /* END=0x10000,
> size 128 as 64 2-byte segments */
>   …
> }
> 
> I need the bootloader’s init code and main() function be executed upon
> power up of the microcontroller. And this would be the case if I only
> flash the bootloader’s .elf onto the flash (0xFFFE pointing to
> bootloader’s main() function).
> 
> But when I then program the application’s image onto the flash the
> 0xFFFE will point to the application’s reset vector which is not a
> bootloader anymore. I'd like to configure my application so that it
> always fills 0xFFFE with a fixed address (0x4400).
> 
> The rest of the story is that when bootloader is started then of
> course the bootloader needs to jump to and execute the application’s
> entry point (0x5400) including the app's watchdog preparation, stack
> init etc.
> 
> Is that doable? How can I define in the application’s code that the
> reset vector (0xFFFE) shall contain the bootloader’s init code
> (0x4400)?
> 
> Best Regards,
> Tomek
> 
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