Issues with Rpi Pico and Skr Pico (rp 2040)

two_cees · February 18, 2023, 5:36pm

Hi. I have been using le potatos to run klipper on my 3d printers for about a month now and they have been working fantastic.

Unfortunately, I have just encountered a small issue I am hoping to fix. When I tried to use a le potato for a voron build, the le potato did not see the attached pico/ rp2040-based devices (a picobilical and an skr pico MCU) on power up. Pressing the reset button on each 2040 board then allowed them to show up to the le potato (using lsusb) and work without issue. Curiously, this is somewhat well known issue with raspberry pi 4’s, but that does not effect raspberry pi 3’s at all. My issue was actually worse using a rpi 4, because the pico’s would not even allow the rpi4 to boot unless reset, while the libre booted all the way and just never showed the usb devices. I was someone hoping might know of a work around for getting the le potato to see the rp2040’s without resetting them. The issue appears regardless of how the le potato is powered (wired to stepdown converter then printer power supply, or powered via a canakit pi3 adapter. Thanks!

Below are some threads discussing the bug in the rp2040:

github.com/bigtreetech/SKR-Pico

Pressing the restart button is needed always

opened 08:10PM - 30 Jan 22 UTC

dgrammatiko

So I followed the instructions about getting a new firmware on the Pico, eg: on …a plain board jumper on the usb-power, adding the boot number pressing the restart button then copying the file removing the boot number and then pressing the restart button. The problem is that I always need to kill the Klipper service then press the restart button on the board and then restart the Klipper service ```bash Use raspi-config to set the country before use. pi@raspberrypi:~ $ ls /dev/serial/by-id/* ls: cannot access '/dev/serial/by-id/*': No such file or directory pi@raspberrypi:~ $ sudo service klipper stop pi@raspberrypi:~ $ sudo service klipper stop pi@raspberrypi:~ $ sudo service klipper stop pi@raspberrypi:~ $ sudo service klipper start pi@raspberrypi:~ $ ls /dev/serial/by-id/* ls: cannot access '/dev/serial/by-id/*': No such file or directory pi@raspberrypi:~ $ sudo service klipper stop pi@raspberrypi:~ $ sudo service klipper start pi@raspberrypi:~ $ ls /dev/serial/by-id/* /dev/serial/by-id/usb-Klipper_rp2040_45503571280EB038-if00 ``` I guess there's a bug in the boot loader

github.com

matthew-humphrey/3DP-Build-Log/blob/main/RP2040-USB-Bug/README.md

## RP2040 USB Bug
This is a brief note to document an issue I have experienced with some 3D printer related controller boards that utilize the RP2040 chip from the Raspberry Pi Foundation. The issue manifests when one of these RP2040-based boards is plugged in via USB to a Raspberry Pi. Upon initial power up of both devices, everything functions normally. However, if you reboot the Raspberry Pi without resetting or cycling power to the RP2040, the Raspberry Pi will not complete a USB connection to the RP2040 and it will vanish from the bus. Power cycling or resetting the RP2040 resolves the issue.

This problem is caused by a bug in the first stage bootloader that is encoded in the (hardened) ROM on the RP2040. Because this bootloader is contained in the device's ROM, it can not be flashed to install an update that fixes the bug. 

I have personally observed or seen reports of this issue on a number of RP2040-based boards, including BigTreeTech SKR Pico, LDO Picobilical, and various "portable input shaper" solutions.

## Impacted Devices

At least one of the USB issues only occurs on RP2040 of the B0 and B1 steppings. RP2040 with steppings of B2 and later made a change to fix a USB issue. However, there are still reports of USB-related boot visibility issues on devices with the B2 stepping, so it seems it is more complicated than a single bug that was fixed.

The RP2040 stepping is laser-etched on the top of the chip. In the pictures of RP2040 below, you can see an "RP2-B1" on one device, and an "RP2-B2" - on the other. The "B1" and "B2" in these photos indicate the stepping of the device.

   ![RP2040 B1 Stepping](images/RP2040-B1-stepping.jpg) ![RP2040 B2 Stepping](images/RP2040-B2-stepping.jpg)

## Reproducing the Problem

Follow the steps below if you have an RP2040 based device and want to confirm it has the issue, test potential fixes, or otherwise reproduce the issue.

1. Flash whatever firmware (for example, Klipper) is desired on the RP2040 device following the instructions from the manufacturer or software provider.

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librecomputer · February 20, 2023, 1:18am

This is probably due to how the RP2040 MCU code is operating. It enumerate once and does not enumerate again unless the hardware is reset. That’s where the fix should go. There’s no way to reset power to the RP2040 from the Le Potato without turning the 5V regulator for USB and HDMI off. If your application does not use HDMI, you can manually turn off the regulator and turn it back on and the RP2040 should enumerate.