Date: Tue, 7 Jan 1997 13:43:51 +1030 (CST) From: Michael Smith <msmith@atrad.adelaide.edu.au> To: tony@dell.com (Tony Overfield) Cc: bde@zeta.org.au, grog@lemis.de, msmith@atrad.adelaide.edu.au, hackers@FreeBSD.ORG Subject: Re: Ints (fwd) Message-ID: <199701070313.NAA07327@genesis.atrad.adelaide.edu.au> In-Reply-To: <3.0.1.32.19970106032347.0067e4ac@bugs.us.dell.com> from Tony Overfield at "Jan 6, 97 03:28:09 am"
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Tony Overfield stands accused of saying: > > There is a scheme for sharing ISA edge-triggered interrupts that > involves pulsing. It works by declaring that the IRQ will remain > high (by pull-up, not driven) until a device wants interrupt service. > At that time the device pulses the IRQ low for 100-200 ns and then > releases it again to cause the rising edge. Eventually, the interrupt > occurs, and the interrupt service routine(s) must then check all the > registered devices to see which one(s) caused the interrupt. Because > the IRQ is pulled high by the pull-up resistor, spurious interrupts > won't be generated. This may seem peculiar, but I've seen it in > operation. It's highly suboptimal; with the specified 2.2K pullup and assuming 60pf of line capacitance (conservative) you get a risetime of over 130nsec (hey, got the right number of zeroes this time 8), which is grossly out of spec for any logic family on the market these days. An edge that slow can actually cause serious problems if it has any noise on it. > Tony -- ]] Mike Smith, Software Engineer msmith@gsoft.com.au [[ ]] Genesis Software genesis@gsoft.com.au [[ ]] High-speed data acquisition and (GSM mobile) 0411-222-496 [[ ]] realtime instrument control. (ph) +61-8-8267-3493 [[ ]] Unix hardware collector. "Where are your PEZ?" The Tick [[
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