Hacks, hints, and tricks

A resting place for important technotes that don't fit anywhere else.

Hacks

I2C debugging

The kernel will lock I2C devices, making it impossible to use userspace tools to debug an issue. To get around this, modify drivers/i2c/i2c-dev.c and remove the EBUSY return statement. E.g. there's a function that either returns 0 or -EBUSY, make it always return 0.

Then you can use the i2c utilities to access devices that are in use.

Linux kernel debugfs

/sys/kernel/debug

contains helpful debugging infos. To mount this, use this command (assuming you've compiled in said support):

mount -tdebugfs none /sys/kernel/debug

Hints

Using a serial port

To use a plug-in USB serial port with screen, you need to be part of the "dialup" group.

sudo vigr

And add your username to the end of the "dialup" line

sudo vigr -s

And add your username yet again to the end of the "dialup" line

Exit, and log back in. You should be able to do something like

screen /dev/ttyUSB0 115200

and use the USB serial adapter you just plugged in.