PRU UART pins - where?


The PRU Cookbook has two examples for using PRU UART: PRU Cookbook
It seems they are using Serial Debug Header for PRU UART i/o (there’s a picture showing this header where the FTDI cable should be attached). But they configure P9_24 and P9_26 pins to pru_uart mode.
I built and uploaded the firmware to the PRU and ran it. When I connected my FTDI cable to the Serial Debug Header, I saw only Linux console login prompt.
I couldn’t readily connect my FTDI cable to P9 header as they are both female.
Is there any way to get PRU UART i/o on the Serial Debug Header of the BBB, or is it just the mistake in the PRU Cookbook?

No answer here?

I never used a PRU debugger, nor did I read the Cookbook.

But when I need to connect two femals I use such long board connectors

moving the black bar to the middle.

Ok, I assumed there was a typo in the Cookbook and used the P9_17 and P9_18 pins for PRU UART.

If you check the BBB system reference manual [1], sheet 4 shows the Rx and Tx pins on the FDTI connector are connected to the P9_24 and P9_26 pins.


[1] beaglebone-black/BBB_SCH.pdf at master · beagleboard/beaglebone-black · GitHub

They are not. According to the schematic, FTDI connector goes to CPU’s UART 0, while P9_24 and P9_26 are UART 1.

Oops, I stand corrected.

Oddly, the P9 header table[1] shows that both P9_17/P9_18 and P9_24/P9_26 should work.



It will work, it’s just that PRU UART and CPU debug UART are not the same. So you can’t use Serial Debug Header to debug PRU, it seems.

Just be aware that P9-24, P9-26 are also DCAN1 and the only CAN port available if you are using cape EEROMs which use I2C instead of DCAN0. One of the LCD capes I bought that that problem. They could have used a different I/O for the buttons but instead used one of the CAN pins which made it useless for a remote CANopen display and control panel.