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Date:	Tue, 1 Jan 2002 23:06:55 PST7
From:	Peter Skye <pskye@peterskye.com >
Reply-To:	scoug-help@scoug.com
To:	scoug-help@scoug.com
Subject:	SCOUG-Help: SBLive setup

Content Type: text/plain

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Steven Levine wrote:
>
> There's a bit more overhead to check both interrupt
> sources each time an interrupt occurs, but you save
> a context switch when the interrupts are pending for
> both sources at the same time.

The drivers are chained. Typically the first driver asks its hardware
if it needs service; if the hardware does want service then the driver
INs/OUTs the necessary ports. The driver can then either pass the
interrupt down the chain to any other driver which might want it, or
return without passing the interrupt. If the driver doesn't attempt to
pass along the interrupt then that driver can't "share" and should be
loaded first so it receives the interrupt last. Two such drivers cannot
share an interrupt since neither will pass to the other. It's been a
while but as I recall there's a bit in the driver header which the
driver programmer can set to choose either type of behavior.

*Therefore*, you can either disassemble the drivers to see how the
headers are set up *or* you can play with the sequence of the drivers
until you find a sequence that works. :)

- Peter

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