PRU Hardware UART

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1

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!

2

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.

3

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