Radxa Rock 5B: defeault UART not working anymore

#1

Hi,

this is my first post in this forum, so forgive me if I’m not following the possible forum’s rules (didn’t find them). Today I faced a “stupid” issue with the enabled-by-default UART on the ROCK 5B I’m working on: basically, I erroneously put the 3 cables of the USB-to-UART adapter in the wrong place and I put them on pins 4 (+5V), 6 (GND) and 8 (UART TX) instead of pins 6 (GND), 8 (UART TX) and 10 (UART RX). This of course break the cable once I turned on the board, but I thought I would have only to replace the cable with a new one. Instead, after this problem, the UART is not working anymore as intended: it looks like signals (i.e. characters) sent by the UART are encoded in a wrong way (you can see the picture attached for better context) and I really don’t know what happened here. I’m using minicom with the configuration provided in the wiki and of course it worked before this episode. I tried also with other UARTs (e.g. the UART7_m1 (pins 11 and 15)) and the UART7_m2 (pins 24 and 26)) but also them are receiving characters encoded erroneously. Did I break the GPIO pins of the board with this error? Do you have any suggestion for this problem?

Thanks in advance for your help.

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#2

Doublecheck the gnd connection.

#3

Hi @Eric_Woudstra, thank you for your answer. Can you please elaborate a bit more what do you mean by this?

#4

Check both sides of the GrouND wire if the connection is made properly.

#5

The wire should be connected correctly. I have an update on this: at least UART2_M2 (from the dtb uart2: serial@feb50000) which is on the pins 36 and 38, with a baudrate of 115200, is actually working (i.e. I can login into the system). I can see the boot logs of u-boot and the kernel encoded in the strange way (probably because they are printed with the higher baudrate) such as the screenshot I posted before and once the boot phase is finished, the login prompt is available (after pressing enter in minicom). So probably also the other UARTs are still functional if the baudrate has to be changed from the default 1500000 one.

So, only the default UART2_M0 is not working. Di you think this is an hardware problem for the specific pins of that UART?

#6

Actually I’ve realized that all these issues where caused by a wrong type of USB-to-UART cable.
With CH340 cables (as stated in the Documentation page) all the UARTs behave as expected with a baud rate of 1.5M, so no problem at all :sweat_smile:.