Timing out a serial connection?

DiverBob · 2009-02-01 16:16

I haven't found any posts with this particular problem...

I have a serial connection as part of my initialization routine where the connection is initialized, 2 characters are transmitted and then I wait for a response. But it is possible that there may not be any response - using the standard .rx command in FullDuplexSerialPlus.spin the program then hangs at this point until I cut the power. Is there a method for timing out the connection if there is no response after a reasonable amount of time so the rest of the app can run?

Thanks

Bob Sweeney

TreeLab · 2009-02-01 16:20

There is a rxcheck routine that returns immediately; if the result is -1, there was no character ready, otherwise it brings back the first received character (ie the first in the receive buffer). You can put a call to rxcheck in a timing loop to see if a coherent response is obtained in a specific time.

There is an rxtime routine as well that does this for a specific delay, but this blocks the execution cog from doing other things while in the polling loop.

Cheers!
Paul Rowntree

Post Edited (TreeLab) : 2/1/2009 4:25:40 PM GMT

DiverBob · 2009-02-01 16:31

I hadn't been online for about 3 days, I posted my issue, then started reading all the current posts and wouldn't you know it, someone else with a simular issue and solution! Teach me to finish reading before posting!
Thanks for the info, I had looked over the rxcheck command but I guess it didn't sink in that it only checks the rx buffer for input. I can put the rxcheck in a 1 or 2 second timing loop and if the buffer is still empty I can push the app into 'test mode' and run fake data instead of waiting forever for serial data!

Thanks again!

Bob Sweeney

StefanL38 · 2009-02-01 20:32

Hello Bob,

take a look into the RxTime-method inside the FullDuplexSerial-object

best regards

Stefan

DiverBob · 2009-02-01 20:47

I did look at the rxtime routine but for some reason it didn't seem to have a time-out. Can you explain how it is supposed to work?

Bob

Erik Friesen · 2009-02-01 20:59

a:=serial.rxtime(100)

That will try for 100ms and if no response returns -1

StefanL38 · 2009-02-01 21:32

Hello Bob,

you should trust a little more in the comments of the code of FullDuplexSerial

PUB rxtime(ms) : rxbyte | t

'' Wait ms milliseconds for a byte to be received
'' returns -1 if no byte received, $00..$FF if byte

  t := cnt
  repeat until (rxbyte := rxcheck) => 0 or (cnt - t) / (clkfreq / 1000) > ms

  t := cnt

stores a snapshot of the systemcounter in variable t

  (cnt - t) / (clkfreq / 1000)

calculates the amount of time that has been gone since the snapshot

and as this time is MORE than the value of "ms" the waiting inside the repeat until-loop ends

  repeat until "byte received or (cnt - t) / (clkfreq / 1000) > ms

here is a democode showing how it works

CON    
  _clkmode = xtal1 + pll16x
  _xinfreq = 5_000_000

OBJ
  Debug : "FullDuplexSerial" 'serial connection to PC       

  
PUB Main | Char

  Debug.Start(31,30,0,115200) 'start(rxpin, txpin, mode, baudrate) :
  ''       okay '"rx" and "tx" viewed from Propeller-Chip Propeller-Chip-PIN-Tx ----> PC

  Debug.Str(string("START",13))
  Debug.Tx(13)

  repeat
    Debug.Str(string("Wait for 5 seconds to receive a byte...",13))
    Char := Debug.rxtime(5000)

    if Char == -1
      Debug.Str(string("nothing received until Timeout",13))
    else
      Debug.Str(string("received byte:"))
      Debug.Tx(Char)
      Debug.Tx(13)

    Debug.Tx(13)
    Debug.Tx(13)
    Debug.Tx(13)

best regards

Stefan

Maybe I should add a signature like that

"there are two ways of learning programming
1.) a slow one: ask EVERYTHING on the forum three words short
2.) a quick one: try something yourselve - ask the forum 10 sentences long -attaching your code - go adding debugoutput to your code while waiting for the forum-answers

DiverBob · 2009-02-02 22:08

For some reason when I read the comments it just didn't 'click' as to what was happening. Thank you to everyone who answered.

I have been a professional database and applications programmer for well over 20 years, I have studied numerous languages and am proficient in several, but I will be the first to admit that I am not perfect in each language I use. Since spin is only a hobby and I usually am using it when I'm tired in the evenings after a full day of my paid job, sometimes I just don't 'get it' right away. Once I read the posts and checked the serial code I saw what I needed then. Sometimes a little help goes a long way.

So forgive me if I am a little slow sometimes, I think this forum has been a great place to learn no matter what your level of competance. Please have some patience with those who aren't at your level yet.

Bob Sweeney

Timing out a serial connection?

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