Stream Selection

[s.jaglowski]

Hello.

I'm running a programme on an 18F8720. The programme receives input from a port - it doesn't care which as they will be mutually exclusive, but needs to output to the port it received the input from.

I know I can use fprintf(stream,.....); etc. But this means duplicating the fprintf for each response. i.e.
if(commsA)
fprintf(streamA, "output answer");
else
fprintf(streamB, "output answer");

I believe it may be possible to have code which selects the stream thus

if(commsA&&!commsB)
#use rs232(xmit=PIN_C6, rcv=PIN_C7)
;
if(commsB&&!commsA)
#use rs232(xmit=PIN_G1, rcv=PIN_G2,)
;
.
.
.
.
printf("output answer to correct stream");

Assuming it can be done, does anyone know of any problems that might follow from this approach?
Has anyone successfully used this approach or something similar?

Regards,

Steve

[treitmey]

Those are hardware USARTS. I would use streams.
Your second idea looks like your redefining the #use rs232.
But why risk losing data while switching?

I would use the first idea.
Set them once and use IRQ's and 2 sets of buffers.
TX1,RX1,TX2,RX2 buffers.
and have the duplicate printf. But your just moving data to the tx
buffers, so its more like a memcpy.(or like LCD_putc)
I don't think it will be as bad as you think.

[s.jaglowski]

I have tried my proposed approach and it seems to function well enough.

However, I think your caution is probably wise. If I can simplify the streamed approach (using a little more string pointer passing) and do it using streams I will.

Regards,

Steve Jaglowski

[Douglas Kennedy]

treitmey probably has it right.
1) Use a printf(myfunction,"...");
2) In myfunction ( myfunction is called for each char in the formatted output printf produces so direct the passed chars to the output buffer desired.
Let the Tx interrupt isr transmit the char. Or just select the stream and
write the char out with printf(STREAM,"%c",c) fputc(c,STREAM) etc.

[Ttelmah]

I'd go slightly further.
'Encapsulate' the putc function, and have a global 'stream' selector.
So:

[s.jaglowski]

Excellent proposals.

Thanks.

Regards,

Steve Jag