The PSP itself represents an ARM core (ARM Cortex A5[6][circular reference]) with the TrustZone extension which is inserted into the main CPU die as a coprocessor. The PSP contains on-chip firmware which is responsible for verifying the SPI ROM and loading off-chip firmware from it.
Critics worry it can be used as a backdoor and is a security concern.[3][4][5] AMD has denied requests to open source the code that runs on the PSP.
The PSP also provides a random number generator for the RDRAND instruction[10] and provides TPM services.