Wifi Kit 32 rebooting when USB interface connected to Linux PC [RESOLVED]

#1

I have a new stock, not yet programmed, Wifi Kit 32. Initially I had hooked it up to a USB 5V power adapter and it seems to work fine with the default firmware (says Scan start and lists wifi networks) and does that in a loop, which I think is how it is supposed to behave. I then tried hooking it up to the USB port on my Linux PC. It starts up and sometimes gets through 1 or 2 cycles of scanning for networks and displaying them, but fairly quickly it looks like it reboots back to the Heltec logo and the white LED flashes, it will usually reboot a few times back to this logo and then goes black for a period, then starts up again after a bit.

Researching this it sounded like perhaps the USB port was not supplying enough power. So I went out and bought a DC powered USB hub. If I hook it up to the hub, without it being connected to the PC, it works fine. If I then connect the hub to the PC, it will go back to endlessly rebooting. It seems like it has something to do with the USB serial port driver? I see there is some DTR and RTS reset circuitry and I wonder if that is getting triggered. I checked the 5V with a scope and I did not see it go below 5V, when setting a falling edge trigger.

Any tips on how I can troubleshoot this would be appreciated. I turned off hardware flow control on the PC just in case that is causing problems.

#2

It looks to be an issue with DTR/RTS of the CP2102 (cp210x driver) as I suspected. After running the following command from a Linux shell the device is no longer rebooting continuously:
stty -F /dev/ttyUSB0 raw clocal -crtscts -hupcl

Hopefully this saves someone else the headache, since most results I encountered talked about issues with the power supply.

#3

Looks like I spoke too soon. While the stty command listed in the previous message does seem to help, attempting to do a flash update fails intermittently at different points in the process. Putting a scope on the CHIP_PU line shows very short negative pulses (~3.8us or so) which happen occasionally and at the point when the flash operation fails. I’m not yet sure what is causing this blip, but I suspect it is still RTS or CTS.

#4

This turned out to be an issue with another daemon which was accessing the /dev/ttyUSB0 port. I have a CyberPower UPS which I installed the management software for. While I don’t currently have the UPS connected to the PC, it apparently still monitors USB tty ports and periodically changes settings on them. Disabling this daemon fixed my software load issues on the Heltec Wifi Kit 32!

So if you’re on Linux and have issues with intermittent timeouts and load failures with esptool.py, check to see if some other application is trying to monitor your USB serial ports.