My name is Peter Keller, and I have joined this list because I have come
to the end of my wits and I need outside help to get the information I
need. The information that I seek does not appear to be in the archives
(but they were helpful), nor documented anywhere that I can see. So,
here I am.
So, I might as well get on with it. :)
I am using the parport device drivers (ppdev) on a linux 2.4.0-test8 kernel.
I have set the bios on the machine to enable EPP mode. The bios is old
and doen't have the EPP+ECP mode that newer bioses have. I only desire
EPP mode anyway.
Now, I built a very simple breakout box that showed that I could correctly
write to the parallel port in standard mode. I could read from the status
pins and mess with the control lines. This all apparently works and with
Then, I built a piece of hardware that spoke EPP. It doesn't work. :)
My question comes in the form of how do I read and write ADDRESS versus DATA
In the book that I have:
Programming the Parallel Port: Interfaceing the PC for Data Acquisition and
Process Control, Gadre, Dhanajay
It states that there are address strobes and data strobes that can be written
or read from by coercing a BASE_ADDRESS + MAGIC_OFFSET the correspondes for
each type of read/write, address, or data. The book goes on to show timing
diagrams that states which signals do what, and for what context.
However, I looked through ppdev.h and noticed that there isn't a clearly
defined interface for me to tell the parport to read/write an address cycle
or a data cycle. There is in parport.h, but it looks like I need to be in
a kernel driver to use it correctly. Is that the case?
This is causing me no end of headaches as I don't know what to make of it.
For instance, when I do this:
(grabbed from another message by Derek Bouius)
int mode2 = IEEE1284_MODE_EPP;
fd = open ("/dev/parport0", O_RDWR | O_NOCTTY);
ret = ioctl (fd, PPCLAIM);
ret = ioctl (fd, PPNEGOT, &mode2); //negotiates to EPP
ret = ioctl (fd, PPSETMODE, &mode2); // sets the driver states
ret = write (fd, &ch, num); // writes out 0x57 on the port in EPP mode
In what context is the data being written out? Data or Address? Also,
what happens if I don't perform the PPNEGOT? Doesn't the PPSETMODE take
care of the fact that I wanted EPP mode? Is the PPNEGOT a specific thing
for a certain type of printer or some such hardware?
The data appears on the bus, and then the write blocks forever. Now it could
be that I have miswired my NWAIT signal, and I have to inspect it again for
the fourth time to make sure. :)
Also, what does PPDATADIR do? I set it to output mode when I write, and
input mode when I read, but only because it seems sensical to do so.
The hardare I've built needs to know the difference between an address
read/write and a data read/write(I've sortof built a small microcontroller
that I need to feed instructions, and then get the data from it). How do
I do these in ppdev? Also, how can I tell if my parport is even working
at all in EPP mode? The ioctls might have returned success, but how do
I _really_ know?
I'm sorry for the rapid fire of questions, but ppdev looks very cool, and
I seem to be hampered merely by a lack of documentation. :) The archive
was very helpful to getting me as far as I've got and I appreciate the
imformation in it.
I can make all of my code available of need be, it is GPL'ed.
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This archive was generated by hypermail 2b29 : Fri Oct 13 2000 - 02:37:46 EDT