First off, EIC7700 has several CPUs. MCPU (P550 cluster) + SCPU (E21) + LCPU (E21) + NPU and DSPs. The SCPU (Secure CPU) is used to run the Masked ROM after power on. The Masked ROM has the logic of loading different payloads from the selected boot source image and kickstarts other CPUs such as MCPU. Optionally it can also validate the cryptographic key/signature of the payload against OTP, thus implementing secure-boot. ESWIN calls the container of the payloads bootchain By default the boot source is QSPI boot flash. The bootchain is stored at the beginning of the flash (offset 0). The boot flash contains the following on my Hifive P550
- DDR init: Vendor binary blob to initialize DDR (closed source)
- "firmware": AFAIK, a very small piece of code that does little to nothing. Perhaps only to keep SCPU active.
- bootloader: The usual opensbi+u-boot stuff that runs on MCPU. (open source, ESWIN maintains the patched opensbi/u-boot)
*As it's shown, the DDR init blob i
