(The AGESA bootloader -- or ABL -- is in the AMD PSP.) In terms of our replacement for AGESA: the PSP boots to our first instruction, which is the pico host bootloader, phbl[0]. phbl then loads the actual operating system[1], which performs platform enablement as part of booting. (This is pretty involved, but to give you a flavor, see, e.g. initialization of the DXIO engine.[2])

[0] https://github.com/oxidecomputer/phbl

[1] https://github.com/oxidecomputer/illumos-gate/tree/stlouis

[2] https://github.com/oxidecomputer/illumos-gate/blob/stlouis/u...