Dear Mark,
The bus timing issue is simple: A 33 mHz Peripheral Connection
Interface (PCI) device will generate a single interrupt for each event.
However, to support legacy devices there's a PCI <-> ISA bridge chip, to
accomodate the parallel, RS-232 serial, keyboard & mouse ports as well
as the ISA boards.
The problem is that the bridge chips don't handle ISA interrupts
too well: Basically, the 4:1 clock speed difference causes each ISA
interrupt to cause 4 interrupts on the PCI bus. OUCH!
Cheers!
Dan
Please CC any replies to me as I'm a DIGEST subscriber. Thanks!
PS: I was part of a team that assembled an Altair 8800, S/N 007, in December
1975
>-----Original Message-----
>From: Mark Plowman [mailto:[EMAIL PROTECTED]]
>Subject: Re: [Leaf-user] loading PCMCIA modules; PCI vs ISA
>
>
>Dan, List,
>
>> From: "Dan Schwartz" <[EMAIL PROTECTED]>
>> Date: Wed, 26 Dec 2001 08:53:25 -0500
>>
><snip>
>>
>> As for using an ISA-> PCM/CIA card - Or in fact any ISA card
> ^^^^^^^^^^^^
>> like a NIC - it's generally Not A Good Idea. As it turns out, the ISA
>> bus runs at 8.3 mHz while the PCI to ISA bridge runs at 33 mHz. This
>> means that every ISA interrupt generates *four* PCI interrupts. Yuk.
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
>Would you care to explain/elaborate this? I can't make head nor tail
>of it. I am a poor soul with a mere twenty years in the
>hardware/software business and I haven't met this one before... ;-)
>
>
>> But, it gets worse: The NIC has to respond to all packets,
>> generating interrupts whether the packet is destined for that machine
>> or not.
>
>And here I was that thinking that software told hardware which MAC
>addresses it had to respond to... ;-)
>
>
>> Cheers!
>> Dan
>
>Seasons greetings
>
>Mark
>
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