From: Of Daniel Mack
> Sent: 18 June 2014 10:28
> To: [email protected]; [email protected]; [email protected]
> Cc: [email protected]; [email protected]; Daniel Mack
> Subject: [PATCH 2/2] usb: musb: cppi41: fire hrtimer according to programmed
> channel length
>
> The musb/cppi41 code installs a hrtimer to work around DMA completion
> interrupts that have fired too early on AM335x hardware. This timer
> is currently programmed to first fire 140 nanoseconds after the DMA
> completion callback. According to the commit which introduced it
> (a655f481d83, "usb: musb: musb_cppi41: handle pre-mature TX complete
> interrupt"), that value is is considered a 'rule of thumb' that worked
> well with the test case described in the commit log.
>
> Test show, however, that for USB audio devices and much smaller packet
> sizes, the timer has to fire earlier in order to correctly handle the audio
> stream. The original test case had output transfer sizes of 1514 bytes, and
> a delay of 140 nanoseconds. For audio devices with 24 bytes channel size, 3
> nanoseconds seem to work well.
You can't really mean nanoseconds?
David
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