Joybus Subsystem

Joybus peripheral interface. More...

Files
file	joybus.c
	Joybus Subsystem.
file	joybus_internal.h
	Joybus internal API.

Macros
#define	JOYBUS_BLOCK_SIZE   64
	Size of a Joybus input/output block in bytes.
#define	JOYBUS_BLOCK_DWORDS   ( JOYBUS_BLOCK_SIZE / sizeof(uint64_t) )
	Size of a Joybus input/output block in double-words.

Functions
void	joybus_exec (const void *input, void *output)
	Write a 64-byte block of data to the PIF and read the 64-byte result.

Detailed Description

Joybus peripheral interface.

The Joybus subsystem is in charge of communication with all controllers, accessories, and peripherals plugged into the N64 controller ports as well as some peripherals on the cartridge. The Joybus subsystem is responsible for communicating with the serial interface (SI) registers to send commands to controllers (including Controller Paks, Rumble Paks, and Transfer Paks), the VRU, EEPROM save memory, and the cartridge-based real-time clock.

This module implements just the low-level protocol. You should use it only to implement an unsupported peripherals. Otherwise, refer to the higher-level modules such as:

For controllers: Controller Subsystem.

For EEPROM, RTC and other peripherals: Peripherals Subsystem.

Internally, the JoyBus subsystem communicates with the PIF controller via the SI DMA, via the JoyBus protocol which is a standard master/slave binary protocol. Each message of the protocol is a block of 64 bytes, and can contain multiple commands. Currently, there are no macros or functions to help composing a JoyBus message, so higher-level libraries currently hard code the binary messages.

All communications is made asynchronously because SI DMA is quite slow: its completion is bound to the PIF actually processing the data, rather than just being the memory transfer. A queue of pending JoyBus messages is kept in a ring buffer, and is then executed under interrupt when the previous SI DMA completes. The internal entry point is joybus_exec_async, that schedules a message to be sent to PIF, and calls a callback with the reply whenever it is available. A blocking API (joybus_exec) is made available for simpler usage.

Function Documentation

joybus_exec()

void joybus_exec	(	const void *	input,
		void *	output
	)

Write a 64-byte block of data to the PIF and read the 64-byte result.

This function is not a stable feature of the libdragon API and should be considered experimental!

The usage of this function will likely change as a result of the ongoing effort to integrate the multitasking kernel with asynchronous operations.

Parameters

[in]	input	Source buffer for the input block to send to the PIF
[out]	output	Destination buffer to place the output block from the PIF