Can't write to TTYs in Ubuntu 20.04 on RPi
by Atoss from LinuxQuestions.org on (#5NVP1)
I have at my hands several devices communicating to a Raspberry Pi over serial links. One of them connects to Pi's own UART, and thus is usually found at ttyS0. Another one connects over USB via an FT230X chip, and thus usually gets ttyUSB0. No idea what chip the 3rd one has, but it pretends to be CDC, and so usually lies at ttyACM0.
This setup worked perfectly with the slightly outdated installation of Raspbian 10 Buster that the Pi was running up to now. However, we're planning to move this particular system to Ubuntu 20.04, so I gave it a trial run. Much to my dismay, when running Ubuntu, I was unable to write to either ttyS0 or any ttyUSB* ports. To elaborate - I can open them from any program just fine (for example, minicom), and if the device at the other end is sending something, the Pi receives without problem, but trying to send anything from the Pi has no result - not even blinking the TX light on a spare FTDI USB-UART dongle I hooked up for tests. CDC-ACM devices still work fine. I should note that for the purposes of testing, I was logged in as root - and I checked the permissions on device files, looked like I should've had both read and write.
I'd be very thankful if someone could point me in the general direction of a solution. Failing that, does anyone happen to know a USB-UART that can do CDC? I have several spare CH340s and some oddball Prolific device, but these all get picked up as ttyUSB.
This setup worked perfectly with the slightly outdated installation of Raspbian 10 Buster that the Pi was running up to now. However, we're planning to move this particular system to Ubuntu 20.04, so I gave it a trial run. Much to my dismay, when running Ubuntu, I was unable to write to either ttyS0 or any ttyUSB* ports. To elaborate - I can open them from any program just fine (for example, minicom), and if the device at the other end is sending something, the Pi receives without problem, but trying to send anything from the Pi has no result - not even blinking the TX light on a spare FTDI USB-UART dongle I hooked up for tests. CDC-ACM devices still work fine. I should note that for the purposes of testing, I was logged in as root - and I checked the permissions on device files, looked like I should've had both read and write.
I'd be very thankful if someone could point me in the general direction of a solution. Failing that, does anyone happen to know a USB-UART that can do CDC? I have several spare CH340s and some oddball Prolific device, but these all get picked up as ttyUSB.