Backchannel usage

[Michael Sweet]

Josh Mathis wrote:
> One quick update - I tried this with a USB printer, and the result was 
> different. I wrote the same status request and read the same way. The 
> read returned -1. However, watching a tail of the error_log, AFTER my 
> filter was done, and the read returned -1, I get a debug message from 
> the USB backend saying that it received 2 bytes of backchannel data. I 
> changed my filter to timeout after 10 seconds on the read, then issue 
> another read. The second one comes back correctly, with the right data 
> from the printer. I have also tried excessive timeouts like 2 minutes, 
> but get the same result - the first read always fails.
> 
> So this raises two questions - why does the parallel backend not get 
> anything at all back, and why does the USB get the return data too late?

What OS?

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______________________________________________________________________
Michael Sweet, Easy Software Products           mike at easysw dot com
Internet Printing and Document Software          http://www.easysw.com