Re: [Sdcc-user] Pointer to SFR

[Alex K. <Al...@Ka...>]

Hi Lanius,

Karl explained this the best. SFRs are NOT addressable indirectly and thus 
you need an instruction for each one. You can't do something like

	mov r0, #80
	mov	a, @r0

because this would access indirect memory not SFRs.

If you wrote an SDCC assembler program to access SFRs it would look 
something like this:

unsigned char getSFR ()
{
_asm
; Return value of SFR
;
; B	in	SFR index (0..128)
; A	out	SFR value
;
	mov	a, #SFRoffset$		; Size of each SFR instruction in table
	mul	ab			; Make into offset
	add	a, #<SFRdispatch$	; Add offset to dispatch table
	push	acc			; Place SFR distpatch address on stack
	mov	a, b
	addc 	a, #>SFRdispatch$
	push	acc
	ret				; "call" into dispatch table will return to our caller

; Each entry is 3 bytes times 128 entries = 384 bytes total
;
SFRdispatch$:
	mov	a, 0x80
	ret
SFRoffset$=.-SFRdispatch$
	mov	a, 0x81
	ret
	mov	a, 0x82
	ret
	; rest of mov	a, 0x... instructions go here
_endasm;
}

Hope this helps.

Alex Karahalios

On Sunday, March 17, 2002, at 05:00  PM, Murray Lang wrote:

> Are the SFRs not memory mapped as well?
> I've used assemblers that don't know about many SFRs and have accessed 
> them simply through their memory locations specified in the MCU 
> documentation. If space wasn't a problem you could define the SFR 
> addresses in a table and step through that table, addressing the SFRs 
> indirectly. Just a thought. I haven't actually tried it.
>
> Regards
>
> Murray
>
> At 10:16 16/03/02 -0600, Karl Bongers wrote:
>>
...
>> So probably a big case statement is your best
>> bet, or the equivalent optimized in asm.
>>
>> Karl.
>>
>>
>> Lanius wrote:
>>
>>> Hi,
>>>
>>> i want to display all *SFR-Register in a loop like:
>>>
>>> for(FSR=firstSFR;SFR<=lastFSR; FSR++)
>>> {
>>>    x= *FSR;
>>>    putChar(x);
>>> }
>>>
>>> how to?
>>>
>>>