0918

1. 杂项设备（misc device）：其实misc_register就是用主标号10调用register_chrdev()的。

 * Register a miscellaneous device with the kernel. If the minor

 * number is set to %MISC_DYNAMIC_MINOR a minor number is assigned

 * and placed in the minor field of the structure. For other cases

 * the minor number requested is used.

 *

 * The structure passed is linked into the kernel and may not be

 * destroyed until it has been unregistered.

2. cat/proc/devices可以查看主设备号， ls -l 则可以看到主次设备号

3.FCLK, HCLK, and PCLK

FCLK is used by ARM920T.

HCLK is used for AHB bus, which is used by the ARM920T, the memory controller, the interrupt controller, the LCD

controller, the DMA and USB host block.

PCLK is used for APB bus, which is used by the peripherals such as WDT, IIS, I2C, PWM timer, MMC interface,

ADC, UART, GPIO, RTC and SPI.