At 19:50 Uhr +0100 17.11.2006, Aaron J. Grier wrote:

[lost clock interrupts]

>I always wondered which device drivers were worst about not letting
>clock ticks run, and seeing if there were ways to "flash" in the driver
>to let the clock ticks update.

The problem may be that the Macintosh is DMAless (apart from the IIfx and
the Quadra 840av, where we don't support the feature), and its cpu does all
I/O. This is as good as a hard realtime constraint: If you "shell out"
from, say, the SCSI driver, to work on a clock interrupt, and don't return
in time, you may lose a SCSI block.

I can say for sure that in the iwm(4) driver, running at splhigh is not to
protect common data structures, but to do realtime work. iwm(4) is
definitely the worst offender here (late-seventies 8-bit technology), and
an alien in a multitasking world...

	hauke

--
"It's never straight up and down"     (DEVO)