Linux USB stability issues

Linux stability issues is a problem from testbed_micropython.

Up to ~6 tentacles work seemless.

The stability isssue have theses root causes

Hub

Power drops. This is solved in https://www.octoprobe.org/octohub4/big_picture.html.

Hubs too deeply cascaded. octohub4 allows to build a very flat structure.

USB protocol stack

USB CDC-ACM requires polling for a serial usb device every ~100ms.

Example: 16 tentacles with ~2 serial lines each: 32 polls every 100ms.

PCI USB host

The are different chipsets. See 30_usb_host.rst

Ubuntu tuning

disable autosuspend

Add kernel boot parameter:

usbcore.autosuspend=-1 pcie_aspm=off

sudoedit /etc/default/grub
sudo update-grub
sudo reboot

keep hubs and CP210x forced on with udev

/etc/udev/rules.d/82-octoprobe_cp210x.rules

ACTION=="add", SUBSYSTEM=="usb", ATTR{idVendor}=="0424", ATTR{idProduct}=="2514", TEST=="power/control", ATTR{power/control}="on"
ACTION=="add", SUBSYSTEM=="usb", ATTR{idVendor}=="10c4", ATTR{idProduct}=="ea60", TEST=="power/control", ATTR{power/control}="on"

sudo udevadm control --reload
sudo udevadm trigger