[cups.development] PPD or backend?
Michael Sweet
msweet at apple.com
Thu Oct 14 08:58:34 PDT 2010
On Oct 14, 2010, at 2:09 AM, Erik de Castro Lopo wrote:
>> On Oct 13, 2010, at 2:23 PM, Erik de Castro Lopo wrote:
>>> ...
>>> So, my question is, can a printer that only requires a PPD file
>>> give me feedback like presence, paper status etc or do I need
>>> to write a CUPS backend driver to get those features.
>>
>> So the short answer is that it can.
>>
>> However, on Linux the current USB backend does not provide back-channel
>> data,
>
> Any idea on what it would take to fix the current USB backend
> for Linux? To me, it seems that it would be smarter to fix all
> the USB backends in one go than doing N printer specific
> backends.
For the libusb-based backend, we'd need to get a newer libusb that supports either access from multiple threads or asynchronous IO.
For the legacy character device backend, we disabled back-channel because too many printers were incompatible with it or we'd get very high CPU usage since some printers always respond to a USB read with a 1284 device ID or some other status information.
________________________________________________________________________
Michael Sweet, Senior Printing System Engineer, PWG Chair
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