I am in the process to migrate a project from a Raspberry Pi 4B to a Rock Pi 4B+. Among others external devices shall be connected via WiFi AP, I2C, 1-Wire and UART to the Rock Pi. To emphasis, the system is running healthy on a Rasberry. I managed to get WiFi AP and 1-Wire up and running on the Rock Pi. Now I got stuck with UART/UART4.
Armbian 22.11.1 Bullseye with Linux 5.15.80-rockchip64
I enabled UART4 via Armbian-Config. Therefore, /boot/armbianEnv.txt shows:
...
overlays=i2c7 uart4 w1-gpio
param_w1_pin=GPIO4_D6
param_w1_pin_int_pullup=1
...
I can take a jump wire and bridge the TX-pin (GPIO1_B0, Pin#19) and RX-pin (GPIO1_A7, Pin#21). When sending bytes to the TX-pin I am receiving them instantly on the RX-Pin. That indicates to me the UART4 is working. On my system the serial port is /dev/ttyS4, with a baud rate of 1000!!. (I am doing this test via Node Red using a standard serial node)
However, if I connect my TTL-signal cable to the RX-pin (TX disconnected), I do not see anything the RX-Pin (however this setup works on the Rasberry).
I have done the same test on UART (/dev/ttyS2) with same result, not showing anything.
I have no experience in Armbian or Rock Pi and would appreciate any hint into which direction to look.
Is the unusual baud rate of 1000 a problem, or
do I need some pull-up resistors or
do I need to compile another dtbo driver like for the 1-wire?