From: Sebastian Andrzej Siewior
> The TX-interrupt fires (sometimes) too early and therefore we have the
> early_tx timer to check periodically if the transfer is done. Initially
> I started I started with a 150us delay which seemed to work well.
> This value was reduced further, because depending on the usecase a
> smaller poll interval was desired.
> Instead of tunning the number further I hereby try to get rid of the
> timer and instead use the TX-FIFO-empty interrupt. I've been playing
> with it for a while and tried various things. Here is a small summary:
>
> - Enable TX-empty interrupt "late"
> The TX-empty interrupt would be enabled after "DMA IRQ" if the FIFO is
> still full. This seems to work in generall but after removing the
> debug code the TX-empty interrupt isn't generated.
>
> - Use one of the two interrups
> In general, the TX-empty interrupt comes after the DMA-interrupt. But
> I've also seen it the other way around. So it not an option.
...
What happens if you don't even enable the 'DMA' interrupt?
If everything is actually working you won't receive a 'TX-Empty'
interrupt until after the dma controller has finished the transfer.
You might want to check the DMA status in the TX-empty interrupt
in case there is a dma underrun mid-frame (probably difficult to
detect near the end of the frame).
If someone has written a DMA interface that requires you take an
'end of transfer' interrupt, then you need to fix the DMA interface!
David
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