How To Guide How to boot from ROM

How to boot from ROM

There are several components which are needed to allow Linux to boot from ROM. Together these provide a very flexible and powerful system. The following sections cover some of these components in more detail, concluding with a worked example.

• The Memory Technology Device subsystem (MTD) is the Linux kernel component which gives easy access to Flash devices. It has many features to simplify handling flash, which are documented in Using the Memory Technology Device (MTD).

• The Initial Program Loader, U-Boot, performs the functions of a simple BIOS; in particular setting up the memory interfaces, providing basic run time services, exercising some control over booting into the main OS, and optionally setting up the root file system.

• Some of the many file systems which are provided with Linux are ideal for use in embedded applications. In particular there is a static (and very compact) ROM file system, a writable Flash file system, and RAM file systems which can be initialized from compressed contents. See File system background and Selecting a file system.

These aspects are brought together in the following sections with a worked example of a typical boot from ROM system in Booting from ROM worked example (Flash).