Above all, debugging the Linux kernel remains a manual process, and the most important developer tool is the ability to print debug messages.

The kernel uses the printk function, which is very similar syntactically to the printf function call from standard C libraries, with the addition of an optional log level. The allowed formats are documented in the kernel source under Documentation/printk-formats.txt.

The printk functionality needs to be compiled into the kernel with the CONFIG_PRINTK configuration variable. You can also configure the Linux kernel to prepend a precise timestamp to every message with the CONFIG_PRINTK_TIME configuration variable, or even better, with the printk.time kernel command-line argument or through sysfs under /sys/module/printk/parameters. Usually all kernels contain printk support, and the Wandboard kernel...