On Sat, 21 Jun 2014, Pedro Erencia wrote: > Hi, > > We are developing an ecg (electrocardiogram) application on an OMAP3 > device (DM3730 ti). > > An acquisition board gets the samples in microseconds and sends them > to the OMAP board via USB. > > This acquisition board does a 16KHz sampling which results in ~4000 > bytes sent every 8ms to the OMAP board; that gives a necessary > throughput of ~0.5MB/s. This acquisition board device is a full-speed > one, and the transfers are done in bulk endpoints, so 64B maximum > packet size. So 500 B/ms, or about 8 64-byte packets per frame. Since the USB limit on full-speed bulk transfers is 19 packets per frame, you're well within the limit. > Given the 1.5 MB/s max _theoretical_ throughput of a full-speed > device, it should be enough. And it is if we connect it on an EHCI > external Host. The problem comes when we try to use the MUSB OTG > configured as host. In that case we get ~300KB/s so the host and the > device became desynchronized and a great mess happens :). > > That could be resolved if we use the EHCI Host Controller with the > full-speed device or the MUSB with a high speed device. Unfortunately, > we cannot do any of that. What happens if you attach the full-speed device to a high-speed hub and plug that hub into the MUSB? 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
