Interleaving Memory Addresses On PCI Boards

[davidc@kbd.com.au (David Chung)]

Hi Everyone,

We are trying to implement two 4Mbyte memory expansion
boards on the PCI bus to get a total of 8Mbytes. We
need a continuous 8Mbyte space with both boards responding
to alternative 8Kbyte pages along the address range in an
interleaved manner.

>From the PCI 2.1 specs it looks like there is NO support
for such set up. I have thought of two tricks and would
appreciate any feedback on them.

(1) On power up, the first board will ask for 8Mbytes 
    while the second board asks for nothing. After POST,
    I configure the second board to respond to the SAME
    address range as the first board (but only to the
    appropriate pages that the first board doesn't cover).

(2) On power up, BOTH boards ask for 4Mbytes. Hopefully,
    the PCI manager will assign them one after another in
    a continuous 8Mbyte range. I then configure BOTH boards
    to respond to the whole 8Mbyte range (again in a page
    interleaved manner).

Thanks in advance for any assistance,
David 

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David Chung                    Internet: davidc@kbd.com.au
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Suite 201, 683 George Street, Sydney, NSW  2000, AUSTRALIA
Tel +61 2 9212 1399                    Fax +61 2 9212 5727
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