PRU Hardware UART

[brc...@gmail.com]

HI,
I'm learning how to use the BBB's PRU's, and I'm writing some assembly to utilize the PRU's integrated UART.  I read through the PRU reference manual and used it to write my assembly code, but after running the code in a debugger, I'm getting almost no output.  The only reaction from the PRU I could see with my logic analyzer is a small spike when the PRU writes a value to the UART output address, but it is not a valid UART communication.

Here's my assembly code and cape manager overlay


Any thoughts as to what might be going on? 

Thanks!

[Charles Steinkuehler]

It looks to me like you're immediately disabling the UART without
waiting for the data you wrote to get transmitted (which will take a
*LONG* time, at least from the PRU's 5 ns/clk perspective). Try either
not shutting down the UART, or polling the UART to make sure the Tx side
is idle before disabling it.

On 7/18/2017 4:09 PM, brc...@gmail.com wrote:
> HI,
> I'm learning how to use the BBB's PRU's, and I'm writing some assembly to
> utilize the PRU's integrated UART. I read through the PRU reference manual and
> used it to write my assembly code, but after running the code in a debugger, I'm
> getting almost no output. The only reaction from the PRU I could see with my
> logic analyzer is a small spike when the PRU writes a value to the UART output
> address, but it is not a valid UART communication.
>
> Here's my assembly code

> <https://gist.github.com/winter-muted/4e4b113fb5767ea31fdae92f334af46a > and
> cape manager overlay
> <https://gist.github.com/winter-muted/6aea7bb9d05636a5304c93c202fbbf67>

>
>
> Any thoughts as to what might be going on?
>
> Thanks!
>

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--
Charles Steinkuehler
cha...@steinkuehler.net

[brc...@gmail.com]

Thanks for the tip.  It turns out I was setting my baud rate incorrectly on the PRU.  After reconfiguring that, there was no issue.

--
Bruce Berry