RevPi Connect S starts glitching if using more than 7 serial ports

[MaltarLED]

Hello,

I am using RevPi Connect S controllers (SKU: 100374), and with them I am using two USB to 4 channel RS485 connverters, so in my /dev/serial/by-path folder I see this tty files:

pi@CPS1:~ $ ls /dev/serial/by-path/
platform-fe980000.usb-usb-0:1.2:1.0-port0
platform-fe980000.usb-usb-0:1.2:1.1-port0
platform-fe980000.usb-usb-0:1.2:1.2-port0
platform-fe980000.usb-usb-0:1.2:1.3-port0
platform-fe980000.usb-usb-0:1.3:1.0-port0
platform-fe980000.usb-usb-0:1.3:1.1-port0
platform-fe980000.usb-usb-0:1.3:1.2-port0
platform-fe980000.usb-usb-0:1.3:1.3-port0
platform-fe980000.usb-usb-0:1.5.2:1.0-port0
platform-fe980000.usb-usb-0:1.5.3:1.0-port0

I am using a ASP.NET application that communicates with fileld devices using the RS485 converters serial ports. I have noticed that if I am using 7 / 8 serial ports (so application comminicates with 7 devices) everything works fine, but if I am using 8 / 8 serial ports (8 devices) the controller starts glitching - the packets on the converter get lost, the controller gets randomly unreachable on the LAN network, the PWR LED starts blinking red and so on…

Is there any explanation to this behaviour? Is there anything I can do to resolve this problem?

Thanks in advance!

Best regards,

Ivan

[nicolaiB]

Hi Ivan,

this is probably related to the USB bus load. On devices like before RevPi Connect 4 the external periphery like ethernet is connected via usb too. Thus if you connect lots of external devices which requires fast response times it can lead to problems. It probably will help, if you enable the XHCI usb controller instead of the default dwc2 one. In order to do this, please proceed with the following steps:

1. sudo nano /boot/firmware/config.txt
2. append the line otg_mode=1 after the line [all]
3. Save the file
4. Reboot

Nicolai