Re: [PARPORT] EPP mode used for EPAT plus
Sat, 22 May 1999 10:36:26 -0400 (EDT)

> I'm trying to write a device driver for the Kodak FD 300 film scanner.
> Unfortunatly I have not been able to obtain any specifications for it, but
> reverse engineering it seems like a challenge. Now it uses a EPAT plus
> chip, presumably for the communications, which linux supports.

The EPAT chip is an ISA bus replicator. It provides a fairly rich set
of configuration options. Without some understanding of what is on
the remote ISA bus, knowing about the EPAT won't help.

> Now my problem is listening to the communication between the computer and
> scanner. Having failed to get any software snooper to work I've decided on
> trying with hardware, and have a design that will enable me to intercept
> the regular EPP communication protocol (read, write, address read and
> address write).
> The problem is that this will fail miserably in case the parallel port
> is used in any other way. So I'm wondering if the EPAT plus chip uses
> anything apart from regular EPP communications?

You'd miss some of the initialisation phase - but in EPP all commands
to the EPAT are delivered with address write. And data transfers use the
standard EPP protocol. If your monitor is interposed in the circuit,
it will have to pass all signals in real-time - merely passing EPP
transactions won't work - as the IEEE 1284 "CPP" is used to enable
and disable the adapter for each individual operation.

> PS: I tried and failed miserably at getting the information by reading the
> source code for the epat driver...

There are two layers of stuff in the EPAT driver - there's code to
talk to the parallel port (in several different modes, depending on the
capabilities of the port) and code that uses the low-level communication
layer to read and write registers in the EPAT itself. Some of those
registers control its operation, others result in i/o cycles on the
remote bus. The job of epat.c is to hide all the EPAT specific details
and export some simple IDE-specific functions to the high level PARIDE
drivers. The EPAT chip is more general, however, and could be connected
to other kinds of devices, not just IDE or ATAPI drives.

I think you'll need to learn something about what's on the other side
of the EPAT before you plan the next phase of your attack.

Grant R. Guenther

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