jumping to code in RAM in a MPC55xx

Tehn Yit Chin tehn.yit.chin at gmail.com
Fri Jul 18 16:29:34 EST 2008


This question is not directly related to linux, but a question on how to
execute code from.

My test code is as follows..

void ram(unsigned int cat) __attribute__ ((section(".ram_code")));
void ram1(void) __attribute__ ((section(".ram_code")));
void flash(void) __attribute__ ((section(".text")));
void flash1(unsigned int y) __attribute__ ((section(".text")));

void ram(unsigned int cat)
    unsigned int abc;

    abc += 12;
    abc += cat;

void ram1(void)

void flash1(unsigned int y)
    unsigned int x;

    x = x + y;


void flash(void)
    unsigned int def;

    def += 12;

    asm (" bel ram1\n\t");

I have the section .ram_code mapped into the internal SRAM of the MPC55xx,
which starts at 0x40000000. Code in .text are mapped into MPC55xx's internal
FLASH, starting at 0x00000000.

When I attempt to link the code together,  I get the error

U:\src\applications\comms/fatdog.c(35,1): relocation truncated to fit:
R_PPC_REL24 against symbol `ram1' defined in .ram_code section in

I googled the error and I think it means that the ram1() is too far away and
the branch address has been truncated to fit into the binary.

Other than assembler bel instruction, I have also tried bl, b and bea and
all of them gave the same link error.

I was wondering if anyone can give some insight on how I can get the MPC55xx
to branch between FLASH and SRAM?

Many thanks,
Tehn Yit Chin
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