On Fri, Sep 12, 2008 at 11:29:39PM +0200, Felix Frey wrote:
> Dear readers
>
> I have a problem with a linux PCI driver I've written. The driver supports a
> kind of a data acquisition system, which is implemented in a programable
> logic device. It's pci interface does not have master capability, so every
> data exchange is initiated by the CPU.
>
> Well, the driver is fairly simple and simply handles data exchange. It has to
> transfer chunks of data from and to the device. To make it fast I'd like to
> use burst transfers, which are supported by the device. Within the driver I
> use the kernel functions memcpy_fromio and memcpy_toio to initiate a
> transfer.
> This works so far, however, there are no burst transfers. The bridge does a
> complete address cycle for every single word which is a big waste of time.
In order to get multiple data cycles per address cycle, either the CPU and/or
the chipset needs to be told it's ok to coalesce the write transactions
(memcpy_toio).
For the equivalent to memcpy_fromio, I suspect one has to implement
a "DMA Master" - a HW component which serves the same function as the
classic 8237A chip:
http://www.cs.sun.ac.za/~lraitt/doc_8237.html
The 8237A basically offloads the polling from the CPU but I don't know if
by itself can enable a device to do "burst mode".
hth,
grant
> I would really appreciate any hint how to make the CPU/bridge to initiate a
> burst transfer. Are there any other functions?
>
> The system is built on a AMD Geode LX800 CPU.
>
> Felix
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