Adrian Smith

imx35 embedded TT limitations?

Discussion created by Adrian Smith on Feb 6, 2012

Hi,

I'm trying to debug a problem supporting usb dacs with the imx35 usb ports.  The issue appears to be related to the embedded transaction translator as when an external hub is attached without any kernel changes the devices work using the hubs TT.

I see description of restricted TT pipe line and the constant:

VUSB_HS_TT_PERIODIC_CONTEXTS

Although the reference manual suggests this can be set lower than 16, can someone confirm whether it is set lower for the imx35.  (its not referenced in the linux 2.6.31 kernel drivers I'm using)

Also does this constant restrict the number of separate transactions or individual start/complete splits which can occur within a frame.

My problem case is support of async usb audio dacs which requires one out iso sitd per frame with 4 start splits and one in iso sitd per frame with 1 start split + 3 complete splits.  With the embedded TT the in sitds never complete, but they do work with the external hub.  [there is also one async QH per 1ms frame]

Thanks,

Adrian

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