Re: Hands on PCI interface ...

From: Nico Coesel (nico_at_puntnl.niks)
Date: 02/04/05 

Date: Fri, 04 Feb 2005 21:15:59 GMT

Jonathan Kirwan <jkirwan@easystreet.com> wrote:

>On Fri, 04 Feb 2005 16:25:30 GMT, nico@puntnl.niks (Nico Coesel) wrote:
>
>>I think it is possible if the ISA card can use 1 interrupt or share
>>interrupts. You'll need some intelligence to convert ISA DMA to PCI
>>bus mastering (which is more or less the same, only the addresses are
>>generated at a different spot).
>
>The problem isn't that, it's the timing requirements of ISA DMA. They simply
>cannot be met by the PCI bus using normal PCI transactions. This is part of why
>the sideband signals are required to the main chipset, so that the chipset can
>be informed about the non-standard nature of certain transactions. Without
>them, the DMA timing itself cannot be supported on the PCI.

I'm convinced it can be done with a trick: have the PCI-ISA bridge
read data from the ISA card first, store this and then send it to the
main memory. This way you separate the timing between the ISA and PCI
bus. This also allows for a smarter scheme in which more data is
buffered in the PCI bridge before it is send to the main memory.
You'll need to have the PCI bridge generate the addresses anyway.
Needless to say, you'll need to change the ISA driver software into a
PCI version as well. 

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