[Linux-parport] Parport woes

John Coppens john at jcoppens.com
Thu Feb 14 12:46:08 EST 2013

Hello people.

I have this homebrew parallel PIC programmer which I've been using for years.
With the advent of parport-less PC, I transferred the programmer to an older
PC. When I tried to run the program, I found that the programmer acted

I wrote a small program in C, which just ioperm's the ports, writes a 
counter to the parport a number of timpes, and releases the port,
and noticed that there were glitches where the bits were set to 0. So I
modified the test program to just write 1's, at a rate of 1000/second.

On the oscilloscope I could then see that the port was regularly (about twice
per second, though not precise) cleared to 0.

I tried: rmmod'ing lp, ppdev, parport, parport_pc (in difference combinations
and one by one). I stopped cupsd. I went into the BIOS and set the parport
to basic SPP operation.

Does anyone have suggestions? Who could be clearing the parport output?
Is there any way to detect which program accesses the port?


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