developing drivers for custom boards

Couple of questions here. Now I know there are VERY good ready made boards out there, but wheres the fun in that?
first question : what interface?

I see EPP parallel port or ethernet . EPP seems a lot easier, but network based I/O feels like it would be nice in the long run. So is a network based I/O even feasible? Developing the I/O card for EPP is really easy, so maybe that needs to be first even if I go for the net based solution later.

second question: Drivers?

I assume a file written in comp is necessary, something simular to the file Andy made for the ISA card in another thread. I don't really want to do stepgen in the card, I really just need to have about 52 I/O on a single port.

So is there any detailed info on creating the comp file? I have read the link Andy pointed to, and I understand the file for the ISA card. I guess I am just looking for somewhere to start.

Third : How to structure the data?

By this I mean send a single address byte to my card followed by some number of data bytes? or an address byte for each data byte? Same question for reading the inputs.

I could use an existing driver for another card, but don't know where to find them.

Thanks in advance for any feedback

Thanks Andy, lots of good stuff here. I think I will settle on a p-port approach, seems the most straight forward. Of course I have made the assumption USB is out of the question.

I think it makes sense to send a fixed number of bytes and read a fixed number. The numbers are TBD, but I am feeling like 5 sent and 4 read. For a whopping 9 byte transfer, I can't see any real value in trying to do random byte access.

I will study on the files posted and see if I can make sense of it.

First question I have is this: I see where 4 bytes get assembled into a 32 bit variable. Is this to make it possible to send the 4 bytes without an adress?

example:
variable = r0 + (r1<<8) + (r2 << 16) + (r3 <<24)
and if I want 5 bytes, will I just need to add +(r4<<32) ?

I guess the same would be true for reading if 4 bytes are read, they will come in as a 32bit variable?

next question:

with this command
how does the p-port know to strobe the address strobe or the data strobe?
for a P-port I would assume R0 is data and base_addr is 0x0378? (or whatever the p-port is at)

how many 8's are in 32?

why 5 of course

R0 = d0-d7
R1= d8-d15 data <<8
R2 = d16 - d23 data <<16
R3 = d24 - d31 data <<24
R4 = d32 - d40 data << 32

Ok, so I know there is only 4 8's in 32, but the first 8 don't count as I understand it. PLEASE correct me if I am wrong.

Well thats the answer to the question I needed to ask but didn't. We can have 32 bit variables. so clearly 4 bytes is the answer. So I will work out the board to be like the PCL720, 32 out and 32 in.

I assume when the time comes, there is a way to transfer a spindle speed? a value from 0-200.

EPP address reads and writes are done at offset 3 from the port base address (so 0x37B) for a PP with 0x378 base address.

www.beyondlogic.org/epp/epp.htm is a good reference on EPP port operation

Perhaps the simplest addressing scheme on a EPP slave device is to write or clear a byte address pointer with address writes and increment that pointer on every data read/write

And yet another Doh! for me. I promise I am getting it. So for data, its base + 4. And clearly the in or out creates write line high or low.

Thanks PCW

I have modified Andy's pcl720.comp file, for what I think seems logical for an EPP driver. If someone doesn't mind looking it over to see if I have modified it properly that would be very nice. Assuming it seems correct, I have a question about using 2 cards (1 on each of 2 different ports). I think I need to create another set of pins, then somehow I need to use those for the read and writes of the second port. But I don't see where just yet.

To get this transition started, I am going to use my current cards set up on seperate ports. That way I don't have to create new hardware just yet. Once I am satisfied I understand what I am doing, I will convert to a single card for all my I/O needs.