From: jes@grendel.demon.co.uk (Jim Segrave) Subject: Re: BUG in 0.99[p1] kernel c Date: 1 Jan 1993 20:23:24 GMT
In article <725836861.AA28902@remote.halcyon.com> Andy.Tainter@f615.n109.z1.fidonet.org (Andy Tainter) writes:
>You *CAN* have more than one card on INT 2, this is a cascaded int and
>you can have upto 7 (may be 6) devices using it...
>
>That is DOS, maybe linux cannot do that, but the hardware is set upto
>do
>it...
This is not quite correct. INT 2 is connected to the interrupt request
output of the second interrupt controller which in turn is connnected to
the ISA bus IRQ8..IRQ15 lines. When one of these lines has an active
high edge, the second controller generates an interrupt request which
then activates the INT 2 input of the master interrupt controller. This
input is NOT connected to any line anywhere on the ISA bus. The
interrupt controllers are programmed for cascade operation on the master's
INT 2 request line so that the interrupt vector passed to th CPU on an
interrupt generated on IRQ8..IRQ15 will get its vector supplied from the
second interrupt controller. Of course Linux upports this, if it didn't,
no non-SCSI disc would work.
None of this has anything to do with sharing a bus IRQ line between cards -
the advice posted earlier is correct - you can not share interrupts
between cards without modifying the motherboard with diode networks. It
may work at first but the long term effect is likely to be component damage.
-- Jim Segrave - Segrave Software Services (jes@grendel.demon.co.uk)