Serial communication impossible under Home Assistant OS

Hi,

I am trying to setup the StromPi3 (rev 1.1, firmware 1.72c) under Home Assistant OS (*).
I have enabled PL011 UART as primary serial and switched miniUART to secondary via config.txt:

core_freq=250

enable_uart=1

dtoverlay=miniuart-bt

I have made sure that the serial console is disabled via cmdline.txt (console=serial0,115200 is not present):

dwc_otg.lpm_enable=0 console=tty1

I have started to fiddle with StromPi in HA OS itself (i.e. not in any docker container) as root.
The serial port device in the OS is present (/dev/serial0 -> ttyAMA0).
When I setup the port via

stty -F /dev/serial0 38400 -a

I get:

speed 38400 baud; line = 0;

intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = <undef>; eol2 = <undef>; swtch = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W; lnext = ^V; discard = ^O;

min = 1; time = 0;

-parenb -parodd -cmspar cs8 hupcl -cstopb cread clocal -crtscts

-ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr icrnl ixon -ixoff -iuclc -ixany -imaxbel -iutf8

opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0

isig icanon iexten echo echoe echok -echonl -noflsh -xcase -tostop -echoprt echoctl echoke -flusho -extproc

(Which is to a letter the same configuration as under Raspbian OS where the communication works.)

When I try to write to the port via

echo -ne 'status-rpi\x0D' > /dev/serial0

and listen via

cat < /dev/serial0

nothing happens, except for breaking the whole StromPi which then needs to be flashed.
This procedure however works under Raspbian OS.

Can you please advise what could be wrong?
I understand I can switch from HA OS to Raspbian OS, but this is the last resort.
I believe the serial communication should be OS-agnostic, besides Home Assistant is known to communicate with serial peripherals without any troubles.

Thanks a lot
Roman

(*)
https://github.com/home-assistant/operating-system/
https://www.home-assistant.io/blog/2021/06/11/home-assistant-os-release-6/
https://developers.home-assistant.io/docs/operating-system/debugging/
https://www.home-assistant.io/common-tasks/os/

I was too quick. I came to a conclusion that HA OS reserves the serial port for itself and trying to interfer leads to a collision.

So instead I tried to make HA to communicate with StromPi. This is what you can try in configuration.yaml:

sensor:

  - platform: serial

    serial_port: /dev/serial0

    name: StromPi Status

    baudrate: 38400

    bytesize: 8

    parity: N

    stopbits: 1

  - platform: command_line

    name: StromPi Handle

    scan_interval: 5

    command: echo -e -n 'status-rpi\x0D' > /dev/serial0

logger:

  default: info

  logs:

    homeassistant.components.serial.sensor: debug

Of course it's not useful this way and needs further programming, but it's a proof o working communication.

Hello Bart,

thank you for sharing your detailed explanation.

We are glad that you could find a way to communicate with the StromPi.

Yours sincerely,

Niklas Tritschler