CFM

https://forum.openwrt.org/viewtopic.php?pid=150142

There is no ROM to boot from; at power up the CPU begins executing the code at the very start of flash. Luckily this isn't the firmware or we'd be in real danger every time we reflashed. Boot is actually handled by a section of code we tend to refer to as the boot loader. In Broadcom devices this is CFE -- "Common Firmware Environment"; think of it like the BIOS in your computer.

The job of the boot loader is to initialize the memory and other hardware and then begin booting the firmware. In most cases there's a recovery mechanism that allows you to reflash the firmware so that a bad flash doesn't render the device useless. CFE does this through the use of a TFTP server; this can be triggered by the firmware not matching the firmware checksum, the boot_wait variable or via CFE's serial console command line.