Kernel Logging Kernel log buffer (default: 64KB) is used to store all kernel log messages. It can be configured from Uboot bootargs (log_buf_len=n) or kernel config option (CONFIG_LOG_BUF_SHIFT=n) where size = 2^n. Logging API’s (printk) are provided to save the data in kernel log buffer from kernel (pr_*()) and device drivers (dev_*()). User can add messages…… Continue reading Linux Debugging
Power ON: GPU turns on when power is applied to Raspberry Pi and ARM CPU is held in reset. ROM Bootloader: GPU runs the on-chip ROM bootloader; loads first stage bootloader in L2 cache memory. First Stage Bootloader: bootcode.bin stored in SD card is the first stage bootloader. bootcode.bin can be compared to UBL bootloader…… Continue reading Raspberry Pi Boot Process
printk function is used to print messages to the console from the kernel source code, same as printf from application. LogLevels in printk are used to classify messages as per the severity. printk(KERN_DEBUG “Print me at Debug Level”); LogLevels KERN_EMERG (0) – Emergency , ususally before crash messages KERN_ALERT (1) – Immediate action required KERN_CRIT (2) – Critical condition / failure KERN_ERR…… Continue reading printk
Kernel keeps registry of interrupt lines, drivers should request for interrupt line and release it when done. Interrupt line can be requested either during init function or during open call of the device driver. Since embedded systems have limited interrupt lines and few are shared between resources it is recommended to hold/request the interrupt during open call…… Continue reading ISR – Linux Device Driver
Kernel modules (device drivers) are event driven. Device drivers register themselves in the kernel during initialization process using module_init() function (Entry point). Initialization function exists only till module is loaded, after that memory of init function is freed. module_exit() function is called during unloading the module, after which device operations cannot be done. Kernel modules run in kernel…… Continue reading Device Driver – Modules
bits4device 