Help with FullduplexSerial

Mike G

I'm trying to wrap my brain around FullDuplexSerial. I'm having difficulty understanding how the jmpret command is working in this context.

                        mov     txcode,#transmit      'initialize ping-pong multitasking 
...
receive                 jmpret  rxcode,txcode         'run a chunk of transmit code, then return 

...
transmit                jmpret  txcode,rxcode         'run a chunk of receive code, then return

I see how calling receive jumps to transmit but what happens next? Does "jmpret txcode,rxcode" cause the receive code to run again?

Leon

Have you looked at the description of jmpret in the manual?

At that point the program alternates between the receive and transmit routines.

Leon

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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle

Post Edited (Leon) : 1/2/2008 8:21:42 PM GMT

Mike G

Why Leon, yes I have read the manual - Jump to address with intention to “return” to another address page 374. I looks to me that the jmpret would ping-pong between the two addresses forever and never execute the code below. Obviously that's not what is happening.

Paul Baker

Hi Mike, pay a little closer attention to the labels provided for JMPRET, you'll see the source operand is the "destination address" and the destination operand is the "return address". So the first line primes the jump to the transmit section of code, the next line stores the current program counter + 1 into the register labeled rxcode (the re-entry point back into the receive code), then a JMP to the address contained in txcode is taken (to the primed address for the transmit code). When the third line is executed the reverse takes place, PC+1 is store in register txcode and a jump is made to the address contained in rxcode.

I think your confusion stems from the destination address being store in the source operand (where one would naturally think destination address = destination operand).

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

Leon

jmpret executes the code at the destination address. I don't see the problem.

Leon

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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle

Mike G

Got it!

Thanks Paul

deSilva

Mike,
you will get additional insight reading that thread
http://forums.parallax.com/showthread.php?p=681299
where such techniques have been discussed in detail some time ago...