On Tue, 11 Oct 2011, Markus Rechberger wrote: > Hi Alan, > > On Tue, Oct 11, 2011 at 8:27 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > > On Tue, 11 Oct 2011, Markus Rechberger wrote: > > > >> Hi Greg, Alan, > >> > >> so I just received another device, the device supports Bulk transfers > >> only and only returns jerky data with Linux. > >> Unfortunately I guess it's based on the chipset since the datatransfer > >> needs the lowest common multiple buffersize. > >> The datapackets which I need are 188 bytes big, the EP size is 512 > >> bytes, the buffer needed in order to get working data > >> is 24064 bytes which exceeds the current accepted buffersize in Linux. > >> I'm having exactly the same problem with MacOSX with lower > >> packetsizes, but OSX allows bigger packet sizes so it's easy to fix. > >> It's the same with Windows. > >> > >> Now is there any way to improve this situation? > >> Additional to the video service, the device itself uses software > >> demodulation for digital radio and has several vendor specific parts > >> in userspace. > > > > Instead of using a single 24064-byte transfer, you can try submitting a > > first transfer of 12288 bytes followed by a second transfer of 11776 > > bytes. �This will mean the sixty-sixth 188-byte datapacket will be > > split between the two transfers, but that shouldn't cause any > > difficulty. > > > > (The numbers 12288 and 11776 are the two multiples of 512 closest to > > 12032 = 24064 / 2.) > > > > Just tried this, > this is the order how the read requests were submitted: > > BULK SIZE: 11776 > BULK SIZE: 12288 > BULK SIZE: 11776 > BULK SIZE: 12288 > BULK SIZE: 11776 > BULK SIZE: 12288 > BULK SIZE: 11776 > BULK SIZE: 12288 > BULK SIZE: 11776 > BULK SIZE: 12288 > BULK SIZE: 11776 > BULK SIZE: 12288 > BULK SIZE: 11776 > BULK SIZE: 12288 > > Same issue on Mac and Linux, the returned data is damaged. Damaged in what way? This should return exactly the same data as seven reads of 24064 bytes. The device doesn't see that URB boundaries; all it sees are the 512-byte packet boundaries. Alan Stern -- 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
