Document needed udev rules for USB HID/CDC devices

[maxgerhardt]

It may seem obvious to a long-time Linux user, but avarice for me failed to retrieve the USB product string of the enumerated devices in openhid() (walk->product_string being a nullptr), but that's just when udev rules aren't installed so that the regular user has access to the e.g. CMSIS-DAP based HID devices. The websit linked in #97 mentions this, but doesn't give a general enough udev file to directly use. We should come up with one.

[maxgerhardt]

Indeed it was udev rules. Initially

now

after adding /etc/udev/rules.d/99-atmel-medbg-cmsis.rules as

# mEDBG CMSIS-DAP
SUBSYSTEM=="tty", ENV{ID_REVISION}=="03eb", ENV{ID_MODEL_ID}=="2145", MODE="0666", ENV{ID_MM_DEVICE_IGNORE}="1", ENV{ID_MM_CANDIDATE}="0"
SUBSYSTEM=="usb", ATTR{idVendor}=="03eb", ATTR{idProduct}=="2145", MODE="0666", ENV{ID_MM_DEVICE_IGNORE}="1"

and doing

sudo udevadm control --reload-rules
sudo udevadm trigger

and replugging the device.

[dl8dtl]

The question is where this might best be documented.

The doc subdirectory contains a bit of documentation, but nothing like installation instructions.

I think it makes sense we add a toplevel README.md, now that the project is on Github, and document things like basic installation and setup there.

Opinions?

[dl8dtl]

Btw., the usual (Linux) policy would not use mode 0666, but rather 0660, and assign to group plugdev.

Legitimate users are then supposed to be members of plugdev in order to attach that kind of devices.