rpi4-osdev/part13a-gpio-interrupts/include/mb.h

extern volatile unsigned int mbox[36];

enum {
    MBOX_REQUEST  = 0
};

enum {
    MBOX_CH_POWER = 0,
    MBOX_CH_FB    = 1,
    MBOX_CH_VUART = 2,
    MBOX_CH_VCHIQ = 3,
    MBOX_CH_LEDS  = 4,
    MBOX_CH_BTNS  = 5,
    MBOX_CH_TOUCH = 6,
    MBOX_CH_COUNT = 7,
    MBOX_CH_PROP  = 8 // Request from ARM for response by VideoCore
};

enum {
    MBOX_TAG_SETPOWER   = 0x28001,
    MBOX_TAG_SETCLKRATE = 0x38002,

    MBOX_TAG_SETPHYWH   = 0x48003,
    MBOX_TAG_SETVIRTWH  = 0x48004,
    MBOX_TAG_SETVIRTOFF = 0x48009,
    MBOX_TAG_SETDEPTH   = 0x48005,
    MBOX_TAG_SETPXLORDR = 0x48006,
    MBOX_TAG_GETFB      = 0x40001,
    MBOX_TAG_GETPITCH   = 0x40008,

    MBOX_TAG_LAST       = 0
};

unsigned int mbox_call(unsigned char ch);