Alan Stern wrote:
> > The computation itself looks a little strange. Exactly what is it
> trying to accomplish? Apparently it truncates a transfer length if the
> value is too large, and arranges that the truncated DMA buffer ends at
> an address which is evenly divisible by maxpacket.
Yes. Which is just nonsense now that I look at it again.
> Isn't the buffer length more important than the ending address? In
> other words, wouldn't it be more appropriate to do something like this?
>
> if (std->len + dma_len > QTD_MAX_XFER_SIZE) {
> dma_len = ((QTD_MAX_XFER_SIZE - std->len) /
> qset->max_packet) * qset->max_packet;
> ep = dma_addr + dma_len;
> }
We require the total length of the qTD to be a multiple of the max
packet size. So,
if (std->len + dma_len > QTD_MAX_XFER_SIZE) {
dma_len = (QTD_MAX_XFER_SIZE / qset->max_packet)
* qset->max_packet - std->len;
}
David
--
David Vrabel, Senior Software Engineer, Drivers
CSR, Churchill House, Cambridge Business Park, Tel: +44 (0)1223 692562
Cowley Road, Cambridge, CB4 0WZ http://www.csr.com/
Member of the CSR plc group of companies. CSR plc registered in England and Wales, registered number 4187346, registered office Churchill House, Cambridge Business Park, Cowley Road, Cambridge, CB4 0WZ, United Kingdom
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