Backchannel data missing

keens312 keens312 at
Wed Sep 10 02:03:30 PDT 2008

> keens312 wrote:
> > ...
> > In my knowledge, the data from USB should go to Apple IOKit at first, then CUPS system, then my filter.
> >
> > Could you give me some suggestion about how to debug this or get the log about bachchannel?
> Unfortunately, there aren't a whole lot of debug options with the
> current USB backend, however you might try posting this question to
> the Apple printing list as the engineer that does the USB code does
> read that list.
> In general, make sure that your back-channel code handles reading all
> pending data on a regular basis - the pipe is non-blocking and will
> drop new data if you don't read it.
> --
> ______________________________________________________________________
> Michael Sweet, Easy Software Products           mike at easysw dot com
Hi Michael,

This issue still happens, and my test shows that this might be a CUPS issue.

On 10.5, filter uses the backchannel CUPS provided. The manual duplex status code will be missed sometimes (if this time ok, next time it will be missing).

On 10.4, filter uses USBGenericPrinterClass+IPC for backchannel, the manual duplex status code can be received by host every time.

So, could you please help to debug this issue? I can provide the detailed data you want.


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