USB Serial Help

stgislander

Please excuse me for repeating a question I made to the General discussion forum two days ago to this forum. Since I hadn't gotten any replies, I thought this forum may be more appropriate.

I want to pass data to/from a PC. I was thinking about using the USB Host port (USB0) since it can also provide power to the BBB/Bela.

I tried to run the serial comm example program but received an Error opening /dev/ttyUSB0 : No such file or directory message. When I typed ls /dev/ttyUSB* into the IDE console, I received cannot access '/dev/ttyUSB*': No such file or directory error message.

Can my program use USB0, or is it set aside for use by the IDE?

giuliomoro

stgislander I tried to run the serial comm example program but received an Error opening /dev/ttyUSB0 : No such file or directory message

From what device are you trying to access /dev/ttyUSB0 ? From the host or from within Bela?
On Bela, that serial interface is called /dev/ttyGS0. On the host, it depends on your OS. On mine (macos 10.13), it is currently called /dev/tty.usbmodem__bela__6, but the name may be different on your system.

The other issue with using that specific port is that it is currently handled by systemd to provide a login shell to the board, so you'd need to disable that if you want to use it for your purposes, or you'll experience missing bytes during communication. To disable getty login on ttyGS0:

systemctl disable  serial-getty@ttyGS0.service 
systemctl stop  serial-getty@ttyGS0.service

stgislander

Thanks Giulio. I was trying to run the program from within the Bela. I had the project loaded in the IDE and hit the "Build & run" button to see what would happen.

giuliomoro

Right, that one expected a USB-serial device connected to Bela, as I wrote it when working with an Arduino. Arguably, using one of the on-board UARTs (e.g.: /dev/ttyS4) would make for a better example

stgislander

giuliomoro I did see something unusual when using UART4. The keyboard translation between my MTTTY terminal and the Bela was "off". To get the kick drum sound, I had to sent ) from my terminal which was received on the Bela as k. There was no character on my terminal I could send that would be received on the Bela as s. The message back to my terminal from the Bela appeared as gibberish. I need to learn more about setting up the serial ports.

stgislander

I did read on the forum that someone wanted to know if the Host port could be used as a Client port. It appeared that it could be done, but after all the reading I've done I'm thinking using UART4 may be a easier and better option.
It's not that much data and doesn't have to be transmitted that fast.

giuliomoro

stgislander if the Host port could be used as a Client port.

sure, at least on BelaMini, but how would you use that in this context?

stgislander

Since I can't power the Bela through the Host port, it doesn't really buy me anything. The only benefit would be that the device currently being looked at for me to communicate with does not have any physical serial ports. I've made the inquiry if a USB-to-serial converter cable would be allowed. I'm doubtful since this is a marine application.

giuliomoro

Are the baudrates the same at both ends? Are the logic levels the same at both ends?
Try slower baudrates and see if that improves things

stgislander

Ah... it is likely logic levels, but I'll check both. Thanks.

stgislander

That was the problem. There was a logic level mismatch between the Bela and my terminal PC.

giuliomoro

What level was it using?

stgislander

giuliomoro Standard RS-232 levels. It completely slipped my mind until you mentioned it. Fortunately I didn't damage anything. I have some carrier boards for another microcontroller we use, and was able to tap into and use the SN75C3222 RS232 transceiver chip circuit.