machine.reset() on Pico W causes [Errno 2] No such file or directory: '/dev/ttyACM0'

[Arpad Jordan]

I connect to REPL of my Raspberry Pi Pico W from Thonny running on my Raspberry Pi Zero W via USB successfully via /dev/ttyACM0

But whenever I execute machine.reset() I loose /dev/ttyACM0 permanently with error message cycling: [Errno 2] No such file or directory: '/dev/ttyACM0'

I can only recover by rebooting both.

When I issue machine.reset() in a minicom -D /dev/ttyACM0 session after a short interruption with an error message the session reconnects to /dev/ttyACM0 by pressing Enter.

This suggests to me that this has something to do with the difference Thonny and minicom handles machine.reset() so someone might can shed some light into this here.

[Arpad Jordan]

I realised from dmesg on Pi Zero W that machine.reset() on /dev/ttyACM0 causes the Pico W actually connecting back on /dev/ttyACM1 for some reason:

[ 1782.275948] usb 1-1: USB disconnect, device number 2
[ 1782.476026] Indeed it is in host mode hprt0 = 00021501
[ 1782.895736] usb 1-1: new full-speed USB device number 3 using dwc_otg
[ 1782.896170] Indeed it is in host mode hprt0 = 00021501
[ 1783.279255] usb 1-1: New USB device found, idVendor=2e8a, idProduct=0005, bcdDevice= 1.00
[ 1783.279305] usb 1-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[ 1783.279325] usb 1-1: Product: Board in FS mode
[ 1783.279341] usb 1-1: Manufacturer: MicroPython
[ 1783.279357] usb 1-1: SerialNumber: e6614c311b903c31
[ 1783.297138] cdc_acm 1-1:1.0: ttyACM1: USB ACM device

I can change the interpreter in Thonny to this new device and now machine.reset() on this new /dev/ttyACM1 causes the Pico W connecting back to /dev/ttyACM0 again:

[ 1913.026915] usb 1-1: USB disconnect, device number 3
[ 1913.226846] Indeed it is in host mode hprt0 = 00021501
[ 1913.596674] usb 1-1: new full-speed USB device number 4 using dwc_otg
[ 1913.597136] Indeed it is in host mode hprt0 = 00021501
[ 1913.948698] usb 1-1: New USB device found, idVendor=2e8a, idProduct=0005, bcdDevice= 1.00
[ 1913.948748] usb 1-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[ 1913.948768] usb 1-1: Product: Board in FS mode
[ 1913.948785] usb 1-1: Manufacturer: MicroPython
[ 1913.948800] usb 1-1: SerialNumber: e6614c311b903c31
[ 1913.968457] cdc_acm 1-1:1.0: ttyACM0: USB ACM device

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[Arpad Jordan]

I further realised that using Tools / Options / Interpreter / Port / <Try to detect port automatically> provides a reasonable experience automatically alternating between devices /dev/ttyACM[0,1].

I still prefer the behaviour of minicom that closes the device early enough for the kernel to enumerate machine.reset() pico with the same device name but I can appreciate Thonny is a much more complex application and I still enjoy using it :)