USB IEEE1284 gadgets and ppdev

Hi,

Can the USB driver for USB to IEEE1284 gadgets be used with the ppdev interface? I looked through the documentation and couldn't find a mention of this one way or the other. The structures used by parport and the USB stuff look similar, but I couldn't see how to get ppdev to play with the USB driver.

The documentation tells you how to do this using the special driver for those USB to IEEE1284 devices using the USS720 chip, but I have yet to see anything using that available for sale in these parts.

Regards,
Steve

Which driver are you using? It ought to be hooked into the parport stuff (parport_register_driver etc) like USS720, and then it'll work.

Tim.
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Thanks for responding.

As far as I can tell there are only two USB drivers for USB-to-IEEE1284 devices - USS720 for the USS720 device, and usblp for everything else. Is usblp supposed to hook into ppdev? Is there some other device driver I missed?

Regards,
Steve

Not into ppdev; into parport. It ought to use
parport_register_port. (It doesn't, currently.)

Tim.
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I understand that the uss720 driver should register with parport, as it is a USB to parallel port adapter, but the usblp driver should not, as it is just a pass-through to a printer. Do you see any advantage to having usblp registering with parport?

thanks,

greg k-h

Well, it would mean that ppdev could use it. I understand that only a few functions of a normal parallel port could be implemented (read, write, get status).

Alternatively I suppose I could get libieee1284 to grok /dev/usb/lp*. Steve---would that solve the problem that you're running into?

Tim.
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Well, the application is this. A lot of industrial control, embedded processor development interfaces, and other stuff use a parallel port to connect to a PC. The parallel port has gone from some notebooks, and is soon to go from desktops too. I want to access some of those devices through a USB to IEEE1284 cable. If the programming interface is ppdev, that is great - no changes needed for code that already works with a real parallel port. If it requires a somewhat different API, that's no big deal. Being able to bit twiddle to the extent that ppdev allows is pretty important, though. I guess there may be some latency issues slowing the bit twiddling across a USB interface, but nothing's perfect.

Regards,
Steve

Well, usblp wouldn't let you do any more than /dev/lp0 currently does, really. It sounds like you want support for more uss720-like devices.

Tim.
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