Accessing flash memory from the bootloader

In Chapter 3, All About Bootloaders, I mentioned the need for the bootloader to load kernel binaries and other images from various flash devices, and to perform system maintenance tasks such as erasing and reprogramming flash memory. It follows that the bootloader must have the drivers and infrastructure needed to support read, erase, and write operations on the type of memory you have, whether it be NOR, NAND, or managed. I will use U-Boot in the following examples; other bootloaders follow a similar pattern.

U-Boot and NOR flash

U-Boot has drivers for NOR CFI chips in drivers/mtd and has the commands erase to erase memory and cp.b to copy data byte by byte, programming the flash...