C function does not return to assembler

[wackazong]

Hello,

using the sdcc sceleton and the mod_skel I made my own MIOS application (still pretty empty). I can now call an assembler function with multiple variables, and call a C function from assembler, but the C function called from assembler does not return to the assember code. Isn't "return" the correct statement to use?

/////////////////////////////////////////////////////////////////////////////
// This function is called by pca9635
/////////////////////////////////////////////////////////////////////////////
void mod_skel_extfunc(unsigned char val1) __wparam
{
	// Just a dummy empty function
	--mod_skel_var;
	MIOS_MIDI_TxBufferPut(val1);
	return;
}

The asm function looks as follows. The first call sends a MIDI Byte, then nothing more comes, not even the second call directly after the first.

pca9635_interpolate
#if _pca9635_def==1	; note this is using the define from the fix in the asm file!
	incf _mod_skel_var, F, BANKED
#endif
	call _mod_skel_extfunc
	call _mod_skel_extfunc
	movf MIOS_PARAMETER1, W
	call _mod_skel_extfunc
	movf MIOS_PARAMETER2, W
	call _mod_skel_extfunc
	return

ALEXander.

[cimo]

hi

dunno if i ve understood right but:  C functions can t be called form within ASM code, the other way round is possible

[wackazong]

Yes you can. I have another program where I do exactly that. I will have a look at the headers again, maybe something ist missing there.

[cimo]

hi

dunno if i ve understood right

yep probably i don t..

[TK.]

Why do you think, that the C function doesn't return to assembler?

Could it be, that you interpreted the MIDI output incorrectly?

I'm missing a defined value in WREG when mod_skel_extfunc() is called, accordingly anything (maybe invalid MIDI bytes?) will be sent out by the core.

It is btw. a bad programming style if lower level functions (part of your module) are calling upper level functions (part of your application). Was this only done for testing purposes?

Best Regards, Thorsten.

[wackazong]

WREG contains the first parameter value of the C function call, and it is returned correctly. I have a bytewise monitor installed, so it can't be the interpretation of the MIDI signal.

I will try to send the value of WREG via assembler to see whats going on.

BTW: I was just testing the whole functionality of mod-skel, its not really relevant for my program, and I know its not the best programming style, but you never know, it might come in handy.

[TK.]

No - you are calling the external function twice:

call _mod_skel_extfunc

call _mod_skel_extfunc

After the first call, it isn't guaranteed that WREG still contains the previous WREG content

Best Regards, Thorsten.

[wackazong]

Ah, see, that was occuring to me now, too. Thanks! I will check that out.