[cups.development] PPD or backend?

[Michael Sweet]

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.

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Michael Sweet, Senior Printing System Engineer, PWG Chair