MCU connection loss during print, USB connection issues

General Discussion
1

Ender 3 Max
Creality 4.2.2 with TMC2208/HR4998 steppers
Mainsail.
Hosting klipper on an acer aspire 1830t laptop running minimal debian 12 connected via USB.

klippy (9).log (5.3 MB)

dmesgprintfailure.txt (63.9 KB)

I’ve been having persistent USB communication/dropout issues and now its at the point were I cant even finish a print if it goes for longer than an hour or two.

Last print was my second attempt at a 5 hour print, both times MCU lost connection and the print stopped around half way through. The first print was on an identical acer aspire 1830t laptop, only difference is the new one has 4gb instead of 2gb ram, I literally just swapped the HDD from the old laptop into the new thinking the laptops USB bus was causing the issues because Im also having issues with the webcam, its a Microsoft Lifecam Studio and its the only other USB device connected to the laptop, I run it at 15fps 720p mjpeg. Whenever it drops out I have to reboot the laptop a few times/unplug for it to work again.

Despite switching to the new laptop, the usb issues still persist. Webcam dropouts and most importantly the MCU disconnect mid print.

I am using a short, high-quality Milwaukee usb micro-b cable, have tried Corsair, Coolermaster, Razer usb cables that came with PC peripherals but this milwaukee one seems to be the best.

I tried taping off the powered pins in the USB port a few weeks back but this didn’t work the same way it usually does with a raspberry pi, something to do with the laptop requiring a voltage sense in order to initialize the data connection, but I might have to re-address that.

I’m also wondering if there’s a way I can create a modified usb cable with dupont connectors on the other end so I can bypass the printerboard USB port all together and create a direct serial connection through the pins, despite the klipper host being a laptop. If anyone has tried something like this please let me know.

Otherwise, if you’ve had similar issues or can find more information via my klipper log about the causes of the issue it would be much appreciated.

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You may see here: Timeout with MCU / Lost communication with MCU and for the amount of b'Got EOF when reading from device' errors also here: Got EOF when reading from device

3

Thanks, I’m still exploring the issue hardware side, as I mentioned, it wasn’t the laptop itself since its still happening on an identical replacement laptop, my biggest indicator that concerns me is the power backfeeding from the USB host to the printer board, turns out I have a spare HLK-CH340E USB breakout board so I might try wiring it to the LCDs Rx/Tx/GND pins with a shielded ferrite-cored cable.

Since the Creality 4.2.2 already uses a CH340 USB-UART path, all the work of making the cable, wiring the pins, recompiling/flashing klipper will only achieve isolating the laptop USB 5v from the printerboard, so I want to make sure it really is the issue before all the extra complicated steps.

Is there a way I can monitor connection stability after changing something other than just committing to a 5 hour print and hoping for the best?
Does the klippylog show any obvious indicators that the connection is unstable from the get go/start of the print? How can I test this live?

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Yes, https://klipper.discourse.group/t/klippy-log-statistics-and-interpretation

Have a look at your

rttvar
rttvar1741×417 49.5 KB

rttvar values or more the rapid appearance of those values and

ready_bytes
ready_bytes1717×431 40.7 KB

ready_bytes values.

Before you do that, you might try a new USB cable.

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