[coreboot] New to coreboot. Need pointer to startup sequence

I have a need to insert some experimental code (never to be checked in) just before the ECC RAM is initialized. The customer wants a specific test to be done before the ram is zeroed out. I'm new to coreboot and having trouble finding the start point coming from power on. Can someone give me a pointer to the documentation or give a quick summary please?
I have a coreboot dev kit provided by the hardware vendor. Intel Xeon cpu, ECC ram.
Thanks