A few weeks ago I had quite fruitful discussion here about possibility to increase the throughput of the USART in the AT91SAM9260.
At data rata 6Mb/s in synchronous mode I had some data dropped.
Here I would like to share the solution, I've finally found.
I had to reduce functionality of the original atmel_serial driver, and to change the way it passes the data into the user space.
I've removed all the tty and line discipline related functionalities. The data are now transferred not through the "read" function, but by the mmapped buffer.
This solution works reliably at 6Mb/s leaving sufficient amount of CPU power for processing of data.
The sources are available at the alt.sources usenet group. See the post "Lite high speed synchronous mode driver for USART in Atmel AT91SAM9260"
or simply follow the link to Google archive: http://groups.google.com/group/alt.sour ... af6eb62a9b

Thanks a lot for all suggestions, which led me to the above solution.
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Regards,
Wojtek