AM3356: Uart baud rate

Nancy Wang

Part Number: AM3356

Hi,

SDK: ti-processor-sdk-linux-rt-am335x-evm-06.03.00.106

The customer has configured two serial ports in the PRU1 in dts, namely /dev/ttySPRU3 and /dev/ttySPRU4. The output waveform of the serial port output data is normal with an oscilloscope, but the baud rate error is large. The 9600 baud rate actually looks It is about 6K or more. The 4800 baud rate sees more than 3K. But looking at pru_suart.c in the linux driver, there is no interface for setting the pru clock frequency. The code of the pru firmware has not been modified yet.

over 5 years ago

0 Bin Liu over 5 years ago

TI__Guru**** 181016 points

Hi Nancy,

The pru clock frequency uses the default. To modify it, it would be a couple properties in device tree.

The baud rate numbers seem to be about 50% off, so it doesn't look to be clock frequency related. Can you reproduce the issue on Beaglebone Black? I can share the pinmux device tree file I used for Beaglebone Black so that you can easily set it up.

0 Bin Liu over 5 years ago in reply to Bin Liu

TI__Guru**** 181016 points

I just realized the SDK kernel source already includes the device tree file for PRU Soft UART - am335x-boneblack-prusuart.dts.

0 Nancy Wang over 5 years ago in reply to Bin Liu

TI__Expert 8210 points

Hi,

Could you please help share steps or document i can refer to? Thanks！ Customer used am335x-boneblack-prusuart.dts on custom board.

0 Bin Liu over 5 years ago in reply to Nancy Wang

TI__Guru**** 181016 points

Hi Nancy,

Do you mean the document for changing clock? I don't think it is clock issue, which won't cause 50% baud rate difference. Please try if you can reproduce the issue on Beaglebone Black.

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AM3356: Uart baud rate