ISA DMA troubles

We are using a custom board based on a 405GP processor with a PIIX4
Southbridge (providing a PCI to ISA bridge, a DMA controller, an interrupt
controller, ...)
A FDC37C78 floppy disk controller is connected to the ISA bus, use a DMA
and an interrupt line of the southbridge.
Kernel version is 2.4.17 (Monta vista HHL 2.1) -
When we perform WRITE operations to the floppy, dma data sent to the floppy
controller are corrupted.
I try some debug and i saw that when a corrupted data is sent, it was a
data from the previous dma transfer from the same address.
When i dump the memory (with BDI2000) at the end of the transfert,
everything is OK.
Does someone met this problem ? A cache pb ?
How can i go further to debug ?

READ operations seems OK.

Thanks for your help .
Philippe


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