On Sat, 21 Mar 2015, Peter Chen wrote: > On Fri, Mar 20, 2015 at 10:16:49AM -0400, Alan Stern wrote: > > Peter: > > > > Are there any known errata for the root-hub Transaction Translator in > > the Freescale host controllers? > > > > When debugging some problems in an i.MX51 system, I found that the host > > controller would never issue more than 4 full-speed isochronous packets > > in any frame, no matter how many siTDs were linked into the EHCI > > schedule. Sometimes it would issue only 1 or 2 packets, even though > > eight were in the schedule! The behavior was very erratic. > > > > The controller seemed to work okay when the full-speed devices were > > behind a high-speed hub. The problems came up only when the host > > controller was connected to a full-speed hub. > > > > Alan Stern > > > > Hi Alan, > > When look at below imx51 errata, it does not describe this issue, I will > talk with IC guys about it next Monday. > > http://cache.freescale.com/files/dsp/doc/errata/IMX51CE.pdf
Okay, thanks. Here are some more details: In my test, the i.MX51 was connected to a 4-port USB-1.1 hub. Each port had an audio device attached. My test involved transmitting audio data in and out from all four devices at the same time. The audio was 16-bit mono at 32 KHz, so the isochronous bandwidth requirement was 64 bytes per frame for each of the eight endpoints (which is well within the capability of full-speed USB). The siTDs were linked to the frame list with all the OUT transfers before any of the IN transfers in each frame. On my bus analyzer I sometimes saw 4 OUT transfers and no IN transfers, sometimes a mixture, sometimes only 1 or 2 IN transfers. I never saw more than 4 transfers in any frame, even though there should have been 8. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
