Hacks, hints, and tricks
A resting place for important technotes that don't fit anywhere else.
Contents
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
Building a u-boot script
mkimage -T script -C none -n 'Novena Boot Script' -d boot.txt boot.scr
boot.txt is the non-binary gook extractable from boot.scr, or you can look at the git repo to retrieve it.
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.
Bluetooth pairing
Some keyboards don't have a fixed PIN. To pair with them, edit the bluez-simple-agent program:
sudo emacs /usr/bin/bluez-simple-agent
and replace ‘KeyboardDisplay’ with ‘DisplayYesNo’.
This will cause the agent to display the PIN code you have to enter, instead of assuming it's fixed at 0000.
Then you can run
hcitool scan
Pick out the MAC of the device, and run
bluez-simple-agent hci0 [your mac address]
This should pair the two, to unpair you can do
bluez-simple-agent hci0 [your mac address] remove
Now you have to "trust" the device:
bluez-test-device trusted [your mac address] yes
And finally, connect it:
bluez-test-input connect [your mac address] yes
Bluetooth Pairing (alternative)
Run bluetoothctl:
sudo bluetoothctl -a
Find the device to pair with. It should be listed. Otherwise, start a scan.
Pair the device. Note that tab-completion works, and makes things helpful.
pair [your mac address]
The console will give you the PIN code of the keyboard. Type this on the keyboard and hit Enter.
Trust the keyboard:
trust [your mac address]
Getting date and time to work
The system should get date/time automatically when you get an IP address.
If that's not happening, do the following:
sudo rm /etc/udev/rules.d/70-persistent-net.rules
This will remove anything that's interfering with getting the DHCP client to work.
Also make sure that this package exists
sudo apt-get install ntpdate
Novena USB hub
See Novena-usb-hub
Startup scripts and systemd
See https://support.criticallink.com/redmine/projects/arm9-platforms/wiki/Linux_Startup_Process_-_Systemd for help.
