The unipi_tcp_server reports the following error:

sudo /opt/unipi/tools/unipi_tcp_server -p 502 -l 127.0.0.1 --verbose --check-firmware

ARMINIT: Cannot open device /dev/unipispi
ARMINIT: Cannot open device /dev/unipispi
ARMINIT: Cannot open device /dev/unipispi
UniPi TCP Modbus Server: Listening Connection Established RET:3
poll timeout = -1[ms]
Starting primary loop

When trying to communicate with the server, errors are reported: Error reading (using EasyModbus Java library).

This is the environment:

I installed raspios_lite_arm64-2020-08-24 on Neuron S103 (RPI4).
The image is available here: https://downloads.raspberrypi.org/raspios_lite_arm64/images/raspios_lite_arm64-2020-08-24/2020-08-20-raspios-buster-arm64-lite.zip

Next I added the Unipi repository the recommended way:

curl https://repo.unipi.technology/debian/README.apt | bash

Subsequently I installed the following modules:

sudo apt install -y unipi-kernel-modules unipi-firmware unipi-firmware-tools unipi-modbus-tools

Finally I run

sudo systemctl stop unipitcp
sudo /opt/unipi/tools/unipi_tcp_server -p 502 -l 127.0.0.1 --verbose --check-firmware