[PARPORT] Re: keeping up appearances

Joerg Dorchain (dorchain@wirbel.com)
Mon, 22 Feb 1999 15:02:35 +0100

On Mon, Feb 22, 1999 at 01:29:19PM +0000, Philip Blundell wrote:
> Are you saying that the m68k parallel ports just don't work at all without
> interrupts, and they use irqs internally for their own purposes?

The current implementation is only interrupt-driven, though it would be
possible to write a polling version if there is really need to.

If so, this
> is a rather different issue. The high-level parport code is currently built
> on the assumption that interrupts are only generated on transitions of the ACK
> pin (though it's left rather muddy which edge is the active one).

That is what the low-level functions are for: Check if the interrupt comes
from "their" card. If not, exit as fast as possible to let the next
handler get called. If it is "their" interrupt, so what necessary with the
hardware (nothing for the amiga built-in port, reset the irq-bit for the
mfc3), and then call the function the high-level driver supplied (if

So, summa summarum also for m68k the high-level irq function can be sure
to be called only for the "right" interrupt.

> The idea of disabling irqs was simply so that if the currently active driver
> was a polling-mode one, we wouldn't get a flood of useless interrupts.

My idea was that if you have a driver in polling mode (i.e.
PARPORT_IRQ=NONE) the hardware is instructed not to rise any interrupts
for that device (donīt know if this is possible with all current
supportted hardware)


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This archive was generated by hypermail 2.0b3 on Mon 22 Feb 1999 - 09:09:12 EST