On Fri, Oct 14, 2011 at 10:51 AM, James Courtier-Dutton <james.dutton@xxxxxxxxx> wrote: > On 14 October 2011 07:23, Markus Rechberger <mrechberger@xxxxxxxxx> wrote: >> On Fri, Oct 14, 2011 at 7:47 AM, <Valdis.Kletnieks@xxxxxx> wrote: >>> On Fri, 14 Oct 2011 05:42:44 +0200, Markus Rechberger said: >>> >>>> The inflexible device which uses 24064 bytes works with all other >>>> Operating systems by using that value >>>> and gives exactly the same results with other transfer sizes than that. >>> >>> -ENOPARSE. If it's inflexible, >> >> the particular device in question is inflexible yes. >> > Here is what I think the actual situation is. > Your transfers over the USB are done in 512 Bytes chunks. > If the device wishes to send 512 bytes, it sends one chunk. > If the device wishes to send 513 bytes, it sends only one chunk, > missing one byte. > if the device wishes to send 1023 bytes, it sends only one chunk, > missing 511 bytes. > if the device wishes to send 1024 bytes, it sends two chunks, missing 0 bytes. > So, the device is sending 1 too few chunks unless the bytes size > exactly matches the chunk size * n. > Another constraint is the device sends multiples of 188 bytes. > So, unless we can find a lowest common multiple of 188 and 512, there > is no transfer size that will work with this device. The LCM is 24064 > and this is the only value that will work with this device. > > Conclusion: > The hardware on the Linux PC and the kernel on the Linux PC are > working correctly. > Your external USB device has an off-by-one error in its > hardware/embedded software and the hardware/embedded software > manufacturer is not prepared to fix it. > > Workaround in software: Increase MAX from 16384 to 24064 or above. > > My own feeling, throw away this faulty bit of hardware and use a different part. > The hardware is not compatible with USB standards. > I agree with that one, and think this conclusion comes closest to the real issue. I can imagine that the chip fifo has some issues with that one. However the device has been tested for a long time without turning to corrupted data so the only issue remaining is the buffer alignment. Thanks for having a look at all that, I wish all requests would have that kind of review, instead of "I don't believe you, not acceptable, not right solution at all" BR, Markus -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
