dingusppc/zdocs/viacuda.md

Using a combination of a 6522 along with some integrated circuits, the VIA Cuda is a microcontroller that heavily controls system operations. It's largely similar to Egret (used in many 68k Macs), but removes some commands.

The usual offset for a VIA Cuda is IOBase (ex.: 0xF3000000 for Power Mac G3 Beige) + 0x16000. The registers are spaced out by 0x200 bytes on the Heathrow.

Usage

The VIA Cuda is emulated in all Power Macs through an interrupt controller. Early Power Macs also used the Parameter RAM.

Additionally, nodes are included for ADB peripherals, Parameter RAM, Real-Time Clocks, and Power Management.

It can be run either synchronously or asynchronously.

However, the CUDA is also slower than the CPU, thus causing a delay that the OS expects.

Packet Types

Hex	Packet Type
0x00	ADB
0x01	Pseudo
0x02	Error
0x03	Timer
0x04	Power
0x05	Mac II

Device Commands

Hex	Device Command
0x00	Reset Bus
0x01	Flush ADB
0x08	Write ADB
0x0C	Read ADB

Pseudo Commands

Hex	Command Name
0x00	WARM_START
0x01	START_STOP_AUTO_POLL
0x02	GET_6805_ADDRESS
0x03	GET_REAL_TIME
0x07	GET_PRAM
0x08	SET_6805_ADDRESS
0x09	SET_REAL_TIME
0x0A	POWER_DOWN
0x0B	SET_POWER_UPTIME
0x0C	SET_PRAM
0x0D	MONO_STABLE_RESET
0x0E	SEND_DFAC
0x10	BATTERY_SWAP_SENSE
0x11	RESTART_SYSTEM
0x12	SET_IPL_LEVEL
0x13	FILE_SERVER_FLAG
0x14	SET_AUTO_RATE
0x16	GET_AUTO_RATE
0x19	SET_DEVICE_LIST
0x1A	GET_DEVICE_LIST
0x1B	SET_ONE_SECOND_MODE
0x21	SET_POWER_MESSAGES
0x22	GET_SET_IIC
0x23	ENABLE_DISABLE_WAKEUP
0x24	TIMER_TICKLE
0X25	COMBINED_FORMAT_IIC
0x26	(UNDOCUMENTED!)