https://dayzerosec.com/blog/2023/04/17/reversing-the-amd-secure-processor-psp.html
Modern versions of the PSP utilize an on-die ARMv7 Cortex-A5 core, which starts before x86 cores are taken out of reset.
I thoroughly enjoy that every x86 CPU is a whole computer with an ARM chip and x86 co-processor cores in disguise.