A simple application for parallel transmission between Popeller chips.

RichardF · 2007-07-02 20:32

I want to have more than 8 cogs in order to simultaneously process more than 7 sensors; so, I have written a simple program that sends parallel data between two or more Propeller chips·using 9 pins. The below program· simulates two Propeller chips for demo purposes, but I am confident it will work with multiple Propeller chips. Also, I am just sending byte data, but in my application I will be sending longs using 4-byte transmissions. Also, I will need to distinguish which sensors/cogs in the second chip the data is coming from. That is easy also; just send a byte telling the receiver what to do with the next 4 bytes, etc. Note that a wait of (400 + cnt) from the time a receiver ready signal is sent until data can be sent is required. Maybe someone with better knowledge of timing issues can explain why the 400 minimum. Please look this over and give me any ideas for improvement you may have. I must keep it simple because this is a hobby and I won't use anything I don't understand.
Thanks,
Richard

Post Edited (RichardF) : 7/2/2007 9:20:01 PM GMT

rokicki · 2007-07-02 20:53

This looks good. I would recommend using *two* control wires, though, a data strobe and an
acknowledge. The data strobe goes in the same direction as the data, and the acknowledge
goes the other way. You can either send data on both edges, or only on one edge, your
choice. This way you don't need any arbitrary waits, and you can speed up either end as
you want (usually by coding them into assembly). The usual signaling (four phase) is:

send:
   repeat until acknowledge == 0 ' receiver ready
   datawires := byte
   strobe := 1
   repeat until acknowledge == 1 ' receiver got it
   strobe := 0

receive:
   repeat until strobe == 1 ' data on wire
   byteread := datawires
   acknowledge := 1
   repeat until strobe == 0 ' let sender reset
   acknowledge := 0

To do data on each edge, either you *always* send two bytes at a time
and you use something like this:

send:
   repeat until acknowledge == 0 ' receiver ready
   datawires := byte1
   strobe := 1
   repeat until acknowledge == 1 ' receiver got it
   datawires := byte2
   strobe := 0

receive:
   repeat until strobe == 1 ' data on wire
   byteread1 := datawires
   acknowledge := 1
   repeat until strobe == 0 ' let sender reset
   byteread2 := datawires
   acknowledge := 0

or else can just look at your own strobe to
determine what to do:

send:
   repeat until acknowledge == strobe ' receiver ready
   datawires := byte
   strobe := !strobe

receive:
   repeat until strobe <> acknowledge ' data on wire
   byteread := datawires
   acknowledge := !acknowledge

RichardF · 2007-07-02 21:22

rokicki,
Perfect! Thanks.. and I understand it!
Richard

A simple application for parallel transmission between Popeller chips.

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