On Tue, Oct 11, 2011 at 9:05 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > 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? http://sundtek.de/images/dtvjitter2.jpg > 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
