NV3 PMC

PMC (Master Control) is the subsystem that controls all of the other subsystems within Nvidia-based GPUs. The NV3 version is fairly basic: it stores some manufacture-time configuration info, allows disabling and enabling interrupts, reading and writing interrupt status and enabling and disabling most other subsystems of the GPU. Certain subsystems, such as PTIMER, cannot be disabled as they are critical to GPU operation; disabling all subsystems on a running system with the Nvidia drivers installed will typically crash the GPU and probably the computer it is running under too. Additionally, disabling interrupts does not seem to work as intended (see Hardware errata)

NV_PMC_BOOT_0

Its a register