NDS: Move a function to ITCM

[RyouArashi]

Is it possible to only move a certain function inside a C file to ITCM?

In the ds_rules/base_rules there is a ruleset which transfers a complete C file to ITCM by naming the file
somthing.itcm.c, but I want only a certain function in ITCM for speedup.
Plan B would be to move this single function to a separate .itcm.c file.

Since we're on the topic, can I relocate global variables to DTCM or is DTCM reserved for stack only?
(I don't need DTCM vars (yet), so this is just out of curiousity)

[elhobbs]

ndstypes.h defines some handy macros for this

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//---------------------------------------------------------------------------------
// libgba compatible section macros
//---------------------------------------------------------------------------------
#define ITCM_CODE       __attribute__((section(".itcm"), long_call))
 
#define DTCM_DATA       __attribute__((section(".dtcm")))
#define DTCM_BSS        __attribute__((section(".sbss")))

if I remember correctly you need to use a function declaration to get this to work - like so:

Code: Select all

int foo(void) ITCM_CODE;

I would imagine that you declare a variable like so (but I have nor done this myself):

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int global_int DTCM_DATA;

[RyouArashi]

Thanks. I'll try these

[WinterMute]

There are macros in the libnds headers to place code & data in the tcm sections, ITCM_CODE for functions, DTCM_BSS for uninitialised data, and DTCM_DATA for initialised data.

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#include <nds.h>
#include <stdio.h>

ITCM_CODE void itcmfn() {
	iprintf("in itcm %p\n", itcmfn);
}

char dtcmarray[256] DTCM_BSS;
char dtcmstring[] DTCM_DATA = "Hello World";

//---------------------------------------------------------------------------------
int main(int argc, char **argv) {
//---------------------------------------------------------------------------------

	consoleDemoInit();
	
	itcmfn();
	
	iprintf("%s\n",dtcmstring);
	iprintf("dtcmstring %p\ndtcmarray %p\n",dtcmstring,dtcmarray);

	while(1) {
		swiWaitForVBlank();
		scanKeys();
		if (keysDown() & KEY_X) break;
	}
	return 0;
}

caveat: You'll see little to no speed increase from doing this unless you have loops which overrun the cache.

[ritz]

DTCM_BSS? A little naive here, but what is this .sbss section for DTCM? I have not seen this before.

[elhobbs]

isn't that just unitialized data that you want in DTCM?

[ritz]

I guess so. I think I'm just confused by the .sbss part being related to DTCM. I'm not clear as to what the .sbss section is physically.

[WinterMute]

.bss & .sbss are nothing physically, they're simply directives which describe uninitialised data which the linkscript reserves memory for without taking space in the binary file. In our case I've mapped bss to ewram and sbss to dtcm.

[ritz]

Ah, I see now. Thanks for the info.

[HeavyDude]

You'll see little to no speed increase from doing this unless you have loops which overrun the cache.

Can someone explain this to me please?