Mastering Embedded Linux Programming - Second Edition

Phase 1 – ROM code

In the absence of reliable external memory, the code that runs immediately after a reset or power-on has to be stored on-chip in the SoC; this is known as ROM code. It is loaded into the chip when it is manufactured, and hence the ROM code is proprietary and cannot be replaced by an open source equivalent. Usually, it does not include code to initialize the memory controller, since DRAM configurations are highly device-specific, and so it can only use Static Random Access Memory (SRAM), which does not require a memory controller.

Most embedded SoC designs have a small amount of SRAM on-chip, varying in size from as little as 4 KB to several hundred KB:

The ROM code is capable of loading a small chunk of code from one of ...