Hi there!
For an assignment I need to write an "odd" piece of software, a parallel port
hardware emulator.
Before you ask, it's for the http://www.umlinux.de/ project.
The goal is to pretend to a virtual UMLinux machine running on a real Linux
machine that the UMLinux had access to a parallel port (either the real one
or a virtual one, that could also virtually be connected to another virtual
parport).
I found quite some information about SPP/EPP/ECP, Nibble mode, even CPP, ISO
1284 and so on, but of course I don't see through the Linux drivers yet.
So I have some questions:
Is it possible (as an user) to access all parallel-port functionality
(including read/write to status, control and all data registers) using the
/usr/src/linux/drivers/char/ppdev.c driver?
This would make connecting the virtual UMLinux to a real parport easier, as
this wouldn't require the UMLinux system to have root rights.
How is the driver hierarchy (which driver/modules uses what other
drivers/modules or what driver includes which driverzyz.c programs), or how
does input/output 'ripple through' different driver-levels (low-level to
high-level)?
And, most important, how and where do the parport drivers probe which
hardware is present, and how do the most common chipsets react? That's very
important for me to know, and I couldn't find the probing routinges so far.
There must be rules like "if you write XY to register Z and reread it, and
bit a has changed, then the chipset supports EPP, otherwise it's SPP" or
something. I guess. Give me a hint. Tutorial suggestions are welcome, too.
Peter Asemann
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