The MacPmem driver is loaded in to the system to enable access to physical memory. Once loaded, the following Intel Graphics MMIO Registers are read and saved to file:

0x00000 - 0x00FFF    VGA and VGA Extended Registers
0x02000 - 0x02FFF    Primary CS Instruction and Interrupt Control Registers
0x03000 - 0x031FF    FENCE & Per-Process GTT Control Registers
0x03200 - 0x03FFF    Frame Buffer Compression Registers
0x05000 - 0x05FFF    VSC Registers
0x06000 - 0x06FFF    Clock Control and Power Management Registers
0x07000 - 0x07FFF    Reserved Registers (3D internal debug)
0x07400 - 0x088FF    Reserved Registers (GPE debug)
0x0A000 - 0x0AFFF    Display Palette Registers
0x10000 - 0x13FFF    GFX MMIO – MCHBAR Aperture
0x30000 - 0x3FFFF    Overlay Registers
0x60000 - 0x6FFFF    Display Engine Pipeline Registers
0x70000 - 0x72FFF    Display and Cursor Control Registers
0x73000 - 0x73FFF    Performance Counters

Then, other information, for example EFI ranges and the kernel slide value, is gathered from memory and saved to a pmem_info.txt file.
Note Root privileges are required to load MacPmem.kext.