> I think it is possible that the "acknowledge" line from the printer port
> could be a problem. During normal printing every (beat me: it's
> something with the rising or falling edge of the signal...) acknowledge
> from the printer generates an interrupt. But the readback uses the
> acknowledge line too and at the moment there is no code to handle the
> interrupts during reading. Theoretically this is a problem, but I'm not
> sure because a simple reprogramming of the control register disables the
> interrupts. But I'm not able to test it, because I've the printer
> interrupts disabled.
Oh, right. Yeah, we should be able to either suppress the interrupts or
just set a flag so they're ignored. I don't think it's a big problem.
> Your other question about reading the status during writing: At the
> moment of "reading" you are unable to write because the 'SelectIN' line
> sets the printer offline. The same for writes: During a 'write' SelectIN
> commands the printer to be "online". A 'read' operation not respecting
> this would print at least an ascii NULL character. With a flag it is
> possible to control this problem but it is (a little bit) sophisticated
> and means changes distributed over the whole lp driver.
I thought that might be the case. Oh well. It can wait until this
putative rewrite of lp happens then (which I'll do if nobody else
volunteers).
p.