On 09-Jan-02 alf schuster wrote:
> Hi Collegues,
> I have to post another problem I found during developement of a  240
> byte ring-buffer with the PIC 16F876:
> The Problem:
> I have to serve two different interrupt sources:
> 1) an UART interrupt, which occurs some 200 to 2000 times a second
> receiving bytes
> 2) a timer interrupt which occurs every 10ms and reminds me to sent
> 24bytes by means of the UART
> I would like to know whether I did the contex saving during an interrupt
> right, therefore here the code:
> I work with banks 0 to bank 2 (three banks of 80 bytes each). After I
> filled the first bank bank(0) I switch over to the second and so on...
> Did I miss saving some register? The bank indicators(RP0/RP1) are saved
> with the STATUS register! Am I right?
> Within the programm I use the FSR to point indirectly to the created
> buffer either in reception and transmission.
> What happens is, that the code I received looks sometimes a bit
> scrambled after it is output from the transmission routine, almost as
> there would be some interference between interrupts...
> Any help is appreciated and thanks in advance.
> If someone needs the whole asm-source I'll send it one request.!
> Thanks again, Alf schuster
>
>
>  org  0x04
>  int                        ; save contex registers
>      movwf w_temp
>      swapf STATUS,w
>      movwf status_temp
>      movf  FSR,w
>      movwf fsr_temp         ;  registers saved

At this point you do not know which register bank is currently selected.
You need to set the bank select bits RP0/RP1 before acessing any registers.

Also atleast w_temp and status_temp need to be in the common
registers (0x70-7F).  fsr_temp can be in a noncommon register if the PR0/PR1
bits are set after "movwf status_temp".

Peter.

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