Re: Can't burst with an INTEL 440BX AGP Bridge.do burst with an INTEL 440BX AGP Bridge.

Alan Cox (alan@lxorguk.ukuu.org.uk)
Thu, 17 Jun 1999 18:19:15 +0100 (BST)

> When we are using copy_to_user() and copy_from_user() the PCI card won't burst.
> When we do a pci bus analyse, we see that the bridge starts a new transaction
> on the PCI bus for every DWord instead of a continuous burst.

The bridge ought to be doing posted writes which should gather the writebacks.
Do you have posted write enabled

> Table 2 shows that a read transaction is even worse: of course the PCI card
> needs extra TW cycles to respond, but now the initiator waits many cycles
> between transactions.

Read will be worse across PCI, you need the card to do writes to the host
memory. You want to push data around PCI not pull it off things.

> 1. Can we set some bits in the bridge to enable bursting and/or speed up
> transactions?

You may want to read the intel CPU docs about the memory type range
registers and also look at the linux mtrr driver

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