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Old 11-24-2005, 01:32 PM   #1
Mike Davies
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Registered: Jul 2004
Distribution: Custom Linux 3.1/Busybox. Fedora 19, Raspberry Pi
Posts: 94

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Problem with Linux/SX28AC i2c interfacing


This message has been cross posted in Linuxquestions and the SX discussion groups.

Iím having a problem with the standard i2c software for the SX28 microprocessor when interfacing to Linux.

My PC is running Linux & Iím using the parallel port via a Philips design i2c interface based around the 74LS05 and some 10k pull-up resistors to provide the i2c interface, and on the other end of the i2c bus I have an Ubicom SX28AC microprocessor running the standard i2c software Ė of which there appears to be several versions. The version Iím running is the version that runs in the ISR, and in my particular case that is every 6uS.

It all works fine when there isnít much activity on the i2c bus, but if I start hammering the bus with a lot of read/writes, then Linux starts complaining with (typically).

Nov 23 19:22:20 rhobert user.err kernel: i2c-algo-bit.o: Philips Parallel port adapter sendbytes: error - bailout.
Nov 23 19:22:21 rhobert user.err kernel: i2c-algo-bit.o: Philips Parallel port adapter sendbytes: error - bailout.
Nov 23 19:22:22 rhobert user.err kernel: i2c-algo-bit.o: Philips Parallel port adapter sendbytes: error - bailout.
Nov 23 19:22:22 rhobert user.err kernel: i2c-algo-bit.o: Philips Parallel port adapter sendbytes: error - bailout.

This particular error in the Linux kernel is associated with ďarbitration or no acknowledgeĒ on the bus. I have tried enabling more error diagnostics in Linux, but that has the effect of slowing down the bus and then the errors disappear . I don't think it's a timing problem with the SX28 interrupt service, because a thousand read/writes only generates 4 errors, and I'd expect more if the service routine was too slow.

Now, I know I can program around this in C on Linux by testing the read/write error returns and re-issuing the request if it fails, but why is it happening ? has anyone else experienced this ?
 
  


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