LP4330 (or other) - Calling assembly function located in RAM from C that is in Flash

nsmith17044 — Thu, 29 Sep 2016 18:08:57 GMT

I'm using a LPC4330 with LPCXpresso 8.2. In the project, most code runs in place in QSPI at 100MHz but I have some functions I need to run very fast so they are located into RAM.

I've been attempting to determine how to call an assembly function located in RAM. An example of the assembly code is as follows:

    .syntax unified
    .section .ramfunc.$RAM2
    .global   CLZ
CLZ:
   clz r0, r0
   bx lr
   .END

This assembly file is part of the project and built with the GCC tool along with the rest of the project.

In a header file I have the C prototype for this assembly function:

__RAMFUNC(RAM2) int CLZ(int x);

The call to this function from C code that is located in Flash compiles using an address for the CLZ call that is in the middle of some other functions. Therefore I assume something isn't setup right as the linker is just plain confused.

The C code that first attempts to use this assembly function is:

return CLZ(gbMask) - 1;

The instructions that are compiled into flash are (not the indicated veneer address):

14002780:   mov     r0, r10
14002782:   blx     0x14013db0 <__CLZ_veneer>
14002786:   subs    r0, #1

However the CLZ function is located in RAM where I expect it (From the map file):

                [!provide]                PROVIDE (__start_data_RAM2, .)
*(.ramfunc.$RAM2)
.ramfunc.$RAM2
                0x10080000       0x16 ./src/mp3codec/asmmisc.o
                0x10080000                MULSHIFT32
                0x10080006                FASTABS
                0x10080010                CLZ

So, I'm expecting the branch call to be to 0x10080010 but instead it is to some other code. It happens to be some const data that are invalid instructions.

Do I have to do something special to get the C code to link to the assembly properly in the case it is in a different section? I don't get any compile or link warnings that I can find. Seems like this should be throwing a warning or an error as it certainly isn't linking to anything valid.

Re: LP4330 (or other) - Calling assembly function located in RAM from C that is in Flash

avt — Thu, 29 Sep 2016 18:43:06 GMT

As there is a veneer, this means the linker thinks you are calling an ARM function, which is not psooible with a Cortex-M base part. I think you need to tell the assembler that your function is thumb code. I think this is. thumbfunc assembler directive - but double check!

LPC MicrocontrollersのトピックRe: LP4330 (or other) - Calling assembly function located in RAM from C that is in Flash

LP4330 (or other) - Calling assembly function located in RAM from C that is in Flash

Re: LP4330 (or other) - Calling assembly function located in RAM from C that is in Flash