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Date:      Fri, 19 Jul 1996 12:47:51 +1000
From:      Bruce Evans <bde@zeta.org.au>
To:        E00114@vnet.atea.be, alex@fa.tdktca.com
Cc:        freebsd-hardware@freebsd.org
Subject:   Re: Multiple COM ports with same IRQ
Message-ID:  <199607190247.MAA30281@godzilla.zeta.org.au>

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>> ISA boxes can 
>> have hardware installed (accidentally?) with devices sharing the same IRQ, but 
>> the drivers cannot deal with it.

>The sharing of interrupts between ISA devices is an electrical 
>constraint.  When two devices are attempting to use a common IRQ line, 

That's why he only wanted to share them for EISA/ISA boxes :-).

sio should be able to handle it if the hardware permits level triggered
interrupts.  It doesn't depend on the trigger level and doesn't have
board-specific multiport optimizations (only board-specific
initializations for AST boards), so it shouldn't be able to tell the
difference between a a bunch of ports connected to the same level
triggered IRQ and a nondescript non-AST multiport board.

Bruce



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