Date: Tue, 31 Dec 1996 15:31:59 +1100 From: Bruce Evans <bde@zeta.org.au> To: bde@zeta.org.au, hmmm@alaska.net Cc: hackers@freebsd.org Subject: Re: Ints Message-ID: <199612310431.PAA22028@godzilla.zeta.org.au>
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>> >for example - i have both COM ports tied to the same ISR - is there any >> >danger in reading RxBuf1 (lower priority) while SERVICING an RxBuf2 INT? > >> There is extreme danger of this not working at all, for other reasons - >> ISA hardware doesn't support sharing interrupts (at the same time). > >this i have heard - but cannot comprehend! the UART will activate its IRQ >- negotiate with the PIC - and when the PIC acks everything it >INTerrupts the CPU to picks up a vector in RAM to jump to ... >who cares if the address is the same ISR or not ??? >i don't understand! :) The hardware doesn't work like that. The UARTs fight for the IRQ. When one attempts to drive it high, the other is usually attempting to drive it low. The other usually wins. Bruce
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