Awesome

gba-link-connection

A set of Game Boy Advance (GBA) C++ libraries to interact with the Serial Port. Its main purpose is to provide multiplayer support to homebrew games. C bindings are also included for compatibility.

👾 LinkCable.hpp: The classic 16-bit Multi-Play mode (up to 4 players) using a GBA Link Cable!
- 💻 LinkCableMultiboot.hpp: ‍Send Multiboot software (small 256KiB ROMs) to other GBAs with no cartridge!
- 🔧👾 LinkRawCable.hpp: A minimal low-level API for the 16-bit Multi-Play mode.
📻 LinkWireless.hpp: Connect up to 5 consoles with the Wireless Adapter!
- 📡 LinkWirelessMultiboot.hpp: ‍Send Multiboot software (small 256KiB ROMs) to other GBAs over the air!
- 🔧📻 LinkRawWireless.hpp: A minimal low-level API for the Wireless Adapter.
- 🔧🏛️ LinkWirelessOpenSDK.hpp: An abstraction of the official software level protocol of the Wireless Adapter.
🌎 LinkUniversal.hpp: Add multiplayer support to your game, both with 👾 Link Cables and 📻 Wireless Adapters, using the same API!
🔌 LinkGPIO.hpp: Use the Link Port however you want to control any device (like LEDs, rumble motors, and that kind of stuff)!
🔗 LinkSPI.hpp: Connect with a PC (like a Raspberry Pi) or another GBA (with a GBC Link Cable) using this mode. Transfer up to 2Mbit/s!
⏱️ LinkUART.hpp: Easily connect to any PC using a USB to UART cable!
🟪 LinkCube.hpp: Exchange data with a Wii or a GameCube using the classic Joybus protocol!
📱 LinkMobile.hpp: Connect to the internet using the Mobile Adapter GB, brought back to life thanks to the REON project!
🖱️ LinkPS2Mouse.hpp: Connect a PS/2 mouse to the GBA for extended controls!
⌨️ LinkPS2Keyboard.hpp: Connect a PS/2 keyboard to the GBA for extended controls!

(click on the emojis for documentation)

<img alt="rlabs" width="16" height="16" src="https://user-images.githubusercontent.com/1631752/116227197-400d2380-a72a-11eb-9e7b-389aae76f13e.png" /> Created by [r]labs.

💬 Check out my other GBA projects: piuGBA, beat-beast, gba-remote-play, gba-flashcartio.

Usage

Copy the contents of the lib/ folder into a directory that is part of your project's include path. Then, #include the library you need, such as LinkCable.hpp, in your project. No external dependencies are required.
For initial instructions and setup details, refer to the large comment block at the beginning of each file, the documentation included here, and the provided examples.
Check out the examples/ folder.
- Compiled ROMs are available in Releases.
- The example code uses libtonc (and libugba for interrupts), but any library can be used.
- The examples can be tested on real GBAs or using emulators.
- For LinkCable/LinkWireless/LinkUniversal, stress tests are provided to help you tweak your configuration. The LinkUniversal_real ROM tests a more real scenario using an audio player, a background video, text and sprites.
- The LinkCableMultiboot_demo and LinkWirelessMultiboot_demo examples can bootstrap all other examples, allowing you to test with multiple units even if you only have one flashcart.

The files use some compiler extensions, so using GCC is required.

The example ROMs were compiled with devkitPro, using GCC 14.1.0 with -std=c++17 as the standard and -Ofast as the optimization level.

To learn implementation details, you might also want to check out the docs/ folder, which contains important documentation.

Compiling the examples

Running ./compile.sh builds all the examples with the right configuration.

The project must be in a path without spaces; devkitARM and some *nix commands are required.

All the projects understand these Makefile actions:

make [ clean | build | start | rebuild | restart ]

C bindings

To use the libraries in a C project, include the files from the lib/c_bindings/ directory.
For documentation, use this README.md file or comments inside the main C++ files.
Some libraries may not be available in C.
Some methods/overloads may not be available in the C implementations.
Unlike the main libraries, C bindings depend on libtonc.

// Instantiating
LinkSomething* linkSomething = new LinkSomething(a, b); // C++
LinkSomethingHandle cLinkSomething = C_LinkSomething_create(a, b); // C

// Calling methods
linkSomething->method(a, b); // C++
C_LinkSomething_method(cLinkSomething, a, b); // C

// Destroying
delete linkSomething; // C++
C_LinkSomething_destroy(cLinkSomething); // C

👾 LinkCable

(aka Multi-Play Mode)

⬆️ This is the Link Port mode that games use for multiplayer.

The library uses message queues to send/receive data and transmits when it's possible. As it uses CPU interrupts, the connection is alive even if a console drops a frame or gets stuck in a long iteration loop. After such an event, all nodes end up receiving all the pending messages.

screenshot

Constructor

new LinkCable(...) accepts these optional parameters:

Name	Type	Default	Description
`baudRate`	BaudRate	`BAUD_RATE_1`	Sets a specific baud rate.
`timeout`	u32	`3`	Maximum number of frames without receiving data from other player before marking them as disconnected or resetting the connection.
`interval`	u16	`50`	Number of 1024-cycle ticks (61.04μs) between transfers (50 = 3.052ms). It's the interval of Timer #`sendTimerId`. Lower values will transfer faster but also consume more CPU. You can use `Link::perFrame(...)` to convert from packets per frame to interval values.
`sendTimerId`	u8 (0~3)	`3`	GBA Timer to use for sending.

You can update these values at any time without creating a new instance:

Call deactivate().
Mutate the config property.
Call activate().

You can also change these compile-time constants:

LINK_CABLE_QUEUE_SIZE: to set a custom buffer size (how many incoming and outgoing messages the queues can store at max per player). The default value is 15, which seems fine for most games.
- This affects how much memory is allocated. With the default value, it's around 390 bytes. There's a double-buffered pending queue (to avoid data races), 1 incoming queue and 1 outgoing queue.
- You can approximate the memory usage with:
  - (LINK_CABLE_QUEUE_SIZE * sizeof(u16) * LINK_CABLE_MAX_PLAYERS) * 3 + LINK_CABLE_QUEUE_SIZE * sizeof(u16) <=> LINK_CABLE_QUEUE_SIZE * 26

Methods

Name	Return type	Description
`isActive()`	bool	Returns whether the library is active or not.
`activate()`	-	Activates the library.
`deactivate()`	-	Deactivates the library.
`isConnected()`	bool	Returns `true` if there are at least 2 connected players.
`playerCount()`	u8 (0~4)	Returns the number of connected players.
`currentPlayerId()`	u8 (0~3)	Returns the current player ID.
`sync()`	-	Call this method every time you need to fetch new data.
`waitFor(playerId)`	bool	Waits for data from player #`playerId`. Returns `true` on success, or `false` on disconnection.
`waitFor(playerId, cancel)`	bool	Like `waitFor(playerId)` but accepts a `cancel()` function. The library will continuously invoke it, and abort the wait if it returns `true`.
`canRead(playerId)`	bool	Returns `true` if there are pending messages from player #`playerId`. Keep in mind that if this returns `false`, it will keep doing so until you fetch new data with `sync()`.
`read(playerId)`	u16	Dequeues and returns the next message from player #`playerId`. If there's no data from that player, a `0` will be returned.
`peek(playerId)`	u16	Returns the next message from player #`playerId` without dequeuing it. If there's no data from that player, a `0` will be returned.
`send(data)`	-	Sends `data` to all connected players.

⚠️ 0xFFFF and 0x0 are reserved values, so don't send them!

💻 LinkCableMultiboot

(aka Multiboot through Multi-Play Mode)

⬆️ This tool allows sending Multiboot ROMs (small 256KiB programs that fit in EWRAM) from one GBA to up to 3 slaves, using a single cartridge.

Its demo (LinkCableMultiboot_demo) has all the other gba-link-connection ROMs bundled with it, so it can be used to quickly test the library.

screenshot

You can change these compile-time constants:

LINK_CABLE_MULTIBOOT_PALETTE_DATA: to control how the logo is displayed.
- Format: 0b1CCCDSS1, where C=color, D=direction, S=speed.
- Default: 0b10010011.

Methods

Name	Return type	Description
`sendRom(rom, romSize, cancel, [mode])`	LinkCableMultiboot::Result	Sends the `rom`. During the handshake process, the library will continuously invoke `cancel`, and abort the transfer if it returns `true`. The `romSize` must be a number between `448` and `262144`, and a multiple of `16`. The `mode` can be either `LinkCableMultiboot::TransferMode::MULTI_PLAY` for GBA cable (default value) or `LinkCableMultiboot::TransferMode::SPI` for GBC cable. Once completed, the return value should be `LinkCableMultiboot::Result::SUCCESS`.

⚠️ stop DMA before sending the ROM! (you might need to stop your audio player)

🔧👾 LinkRawCable

⬆️

This is a minimal hardware wrapper designed for the Multi-Play mode.
It doesn't include any of the features of 👾 LinkCable, so it's not well suited for games.
Its demo (LinkRawCable_demo) can help emulator developers in enhancing accuracy.

screenshot

Methods

Name	Return type	Description
`isActive()`	bool	Returns whether the library is active or not.
`activate(baudRate = BAUD_RATE_1)`	-	Activates the library in a specific `baudRate` (`LinkRawCable::BaudRate`).
`deactivate()`	-	Deactivates the library.
`transfer(data)`	LinkRawCable::Response	Exchanges `data` with the connected consoles. Returns the received data, including the assigned player ID.
`transfer(data, cancel)`	LinkRawCable::Response	Like `transfer(data)` but accepts a `cancel()` function. The library will continuously invoke it, and abort the transfer if it returns `true`.
`transferAsync(data)`	-	Schedules a `data` transfer and returns. After this, call `getAsyncState()` and `getAsyncData()`. Note that until you retrieve the async data, normal `transfer(...)`s won't do anything!
`getAsyncState()`	LinkRawCable::AsyncState	Returns the state of the last async transfer (one of `LinkRawCable::AsyncState::IDLE`, `LinkRawCable::AsyncState::WAITING`, or `LinkRawCable::AsyncState::READY`).
`getAsyncData()`	LinkRawCable::Response	If the async state is `READY`, returns the remote data and switches the state back to `IDLE`. If not, returns an empty response.
`getBaudRate()`	LinkRawCable::BaudRate	Returns the current `baudRate`.
`isMaster()`	bool	Returns whether the console is connected as master or not. Returns garbage when the cable is not properly connected.
`isReady()`	bool	Returns whether all connected consoles have entered the multiplayer mode. Returns garbage when the cable is not properly connected.

don't send 0xFFFF, it's a reserved value that means disconnected client
only transfer(...) if isReady()

📻 LinkWireless

(aka GBA Wireless Adapter)

⬆️ This is a driver for an accessory that enables wireless games up to 5 players. The inner workings of the adapter are highly unknown, but this blog post is very helpful. I've updated it to add more details about the things I learnt by the means of ~~reverse engineering~~ brute force and trial&error.

The library, by default, implements a lightweight protocol (on top of the adapter's message system) that sends packet IDs and checksums. This allows detecting disconnections, forwarding messages to all nodes, and retransmitting to prevent packet loss.

https://github.com/afska/gba-link-connection/assets/1631752/7eeafc49-2dfa-4902-aa78-57b391720564

Constructor

new LinkWireless(...) accepts these optional parameters:

Name	Type	Default	Description
`forwarding`	bool	`true`	If `true`, the server forwards all messages to the clients. Otherwise, clients only see messages sent from the server (ignoring other peers).
`retransmission`	bool	`true`	If `true`, the library handles retransmission for you, so there should be no packet loss.
`maxPlayers`	u8 (2~5)	`5`	Maximum number of allowed players.
`timeout`	u32	`10`	Maximum number of frames without receiving data from other player before resetting the connection.
`interval`	u16	`50`	Number of 1024-cycle ticks (61.04μs) between transfers (50 = 3.052ms). It's the interval of Timer #`sendTimerId`. Lower values will transfer faster but also consume more CPU. You can use `Link::perFrame(...)` to convert from packets per frame to interval values.
`sendTimerId`	u8 (0~3)	`3`	GBA Timer to use for sending.

You can update these values at any time without creating a new instance:

Call deactivate().
Mutate the config property.
Call activate().

You can also change these compile-time constants:

LINK_WIRELESS_QUEUE_SIZE: to set a custom buffer size (how many incoming and outgoing messages the queues can store at max). The default value is 30, which seems fine for most games.
- This affects how much memory is allocated. With the default value, it's around 960 bytes. There's a double-buffered incoming queue and a double-buffered outgoing queue (to avoid data races).
- You can approximate the memory usage with:
  - LINK_WIRELESS_QUEUE_SIZE * sizeof(Message) * 4 <=> LINK_WIRELESS_QUEUE_SIZE * 32
LINK_WIRELESS_MAX_SERVER_TRANSFER_LENGTH and LINK_WIRELESS_MAX_CLIENT_TRANSFER_LENGTH: to set the biggest allowed transfer per timer tick. Transfers contain retransmission headers and multiple user messages. These values must be in the range [6;20] for servers and [2;4] for clients. The default values are 20 and 4, but you might want to set them a bit lower to reduce CPU usage.
LINK_WIRELESS_PUT_ISR_IN_IWRAM: to put critical functions in IWRAM, which can significantly improve performance due to its faster access. This is disabled by default to conserve IWRAM space, which is limited, but it's enabled in demos to showcase its performance benefits.
- If you enable this, make sure that LinkWireless.cpp gets compiled! For example, in a Makefile-based project, verify that the file is in your SRCDIRS list.
LINK_WIRELESS_ENABLE_NESTED_IRQ: to allow LINK_WIRELESS_ISR_* functions to be interrupted. This can be useful, for example, if your audio engine requires calling a VBlank handler with precise timing.
- This won't produce any effect if LINK_WIRELESS_PUT_ISR_IN_IWRAM is disabled.
LINK_WIRELESS_USE_SEND_RECEIVE_LATCH: to alternate between sends and receives on each timer tick (instead of doing both things). This is disabled by default. Enabling it will introduce a bit of latency but also reduce a lot the overall CPU usage. It's enabled in the LinkWireless_demo example, but disabled in the LinkUniversal_* examples.
LINK_WIRELESS_TWO_PLAYERS_ONLY: to optimize the library for two players. This will make the code smaller and use less CPU. It will also let you "misuse" 5 bits from the packet header to send small packets really fast (e.g. pressed keys) without confirmation, using the QUICK_SEND and QUICK_RECEIVE properties. When this option is enabled, the maxPlayers constructor parameter will be ignored.

Methods

Most of these methods return a boolean, indicating if the action was successful. If not, you can call getLastError() to know the reason. Usually, unless it's a trivial error (like buffers being full), the connection with the adapter is reset and the game needs to start again.
You can check the connection state at any time with getState().
Until a session starts, all actions are synchronous.
During sessions (when the state is SERVING or CONNECTED), the message transfers are IRQ-driven, so send(...) and receive(...) won't waste extra cycles. The only synchronous method that can be called during a session is serve(...), which can be used to update the broadcast data.

Name	Return type	Description
`isActive()`	bool	Returns whether the library is active or not.
`activate()`	bool	Activates the library. When an adapter is connected, it changes the state to `AUTHENTICATED`. It can also be used to disconnect or reset the adapter.
`deactivate()`	bool	Puts the adapter into a low consumption mode and then deactivates the library. It returns a boolean indicating whether the transition to low consumption mode was successful. You can disable the transition and deactivate directly by setting `turnOff` to `true`.
`serve([gameName], [userName], [gameId])`	bool	Starts broadcasting a server and changes the state to `SERVING`. You can, optionally, provide a `gameName` (max `14` characters), a `userName` (max `8` characters), and a `gameId` (0 ~ 0x7FFF) that games will be able to read. The strings must be null-terminated character arrays. If the adapter is already serving, this method only updates the broadcast data. Updating broadcast data while serving can fail if the adapter is busy. In that case, this will return `false` and `getLastError()` will be `BUSY_TRY_AGAIN`.
`getServers(servers, [onWait])`	bool	Fills the `servers` array with all the currently broadcasting servers. This action takes 1 second to complete, but you can optionally provide an `onWait()` function which will be invoked each time VBlank starts.
`getServersAsyncStart()`	bool	Starts looking for broadcasting servers and changes the state to `SEARCHING`. After this, call `getServersAsyncEnd(...)` 1 second later.
`getServersAsyncEnd(servers)`	bool	Fills the `servers` array with all the currently broadcasting servers. Changes the state to `AUTHENTICATED` again.
`connect(serverId)`	bool	Starts a connection with `serverId` and changes the state to `CONNECTING`.
`keepConnecting()`	bool	When connecting, this needs to be called until the state is `CONNECTED`. It assigns a player ID. Keep in mind that `isConnected()` and `playerCount()` won't be updated until the first message from the server arrives.
`send(data)`	bool	Enqueues `data` to be sent to other nodes.
`receive(messages)`	bool	Fills the `messages` array with incoming messages, forwarding if needed.
`getState()`	LinkWireless::State	Returns the current state (one of `LinkWireless::State::NEEDS_RESET`, `LinkWireless::State::AUTHENTICATED`, `LinkWireless::State::SEARCHING`, `LinkWireless::State::SERVING`, `LinkWireless::State::CONNECTING`, or `LinkWireless::State::CONNECTED`).
`isConnected()`	bool	Returns `true` if the player count is higher than `1`.
`isSessionActive()`	bool	Returns `true` if the state is `SERVING` or `CONNECTED`.
`playerCount()`	u8 (1~5)	Returns the number of connected players.
`currentPlayerId()`	u8 (0~4)	Returns the current player ID.
`getLastError([clear])`	LinkWireless::Error	If one of the other methods returns `false`, you can inspect this to know the cause. After this call, the last error is cleared if `clear` is `true` (default behavior).

⚠️ 0xFFFF is a reserved value, so don't send it!

💻 LinkWirelessMultiboot

(aka Multiboot through Wireless Adapter)

⬆️ This tool allows sending Multiboot ROMs (small 256KiB programs that fit in EWRAM) from one GBA to up to 4 slaves, wirelessly, using a single cartridge.

Its demo (LinkWirelessMultiboot_demo) has all the other gba-link-connection ROMs bundled with it, so it can be used to quickly test the library.

https://github.com/afska/gba-link-connection/assets/1631752/9a648bff-b14f-4a85-92d4-ccf366adce2d

Methods

Name	Return type	Description
`sendRom(rom, romSize, gameName, userName, gameId, players, cancel)`	LinkWirelessMultiboot::Result	Sends the `rom`. The `players` must be the exact number of consoles that will download the ROM. Once this number of players is reached, the code will start transmitting the ROM bytes. During the process, the library will continuously invoke `cancel` (passing a `LinkWirelessMultiboot::MultibootProgress` object as argument), and abort the transfer if it returns `true`. The `romSize` must be a number between `448` and `262144`. It's recommended to use a ROM size that is a multiple of `16`, as this also ensures compatibility with Multiboot via Link Cable. Once completed, the return value should be `LinkWirelessMultiboot::Result::SUCCESS`.

🔧📻 LinkRawWireless

⬆️

This is a minimal hardware wrapper designed for the Wireless Adapter.
It doesn't include any of the features of 📻 LinkWireless, so it's not well suited for games.
Its demo (LinkRawWireless_demo) can help emulator developers in enhancing accuracy.

screenshot

Methods

There's one method for every supported Wireless Adapter command.
Use sendCommand(...) to send arbitrary commands.

🔧🏛 LinkWirelessOpenSDK

⬆️ All first-party games, including the Multiboot 'bootloader' sent by the adapter, use an official software-level protocol. This class provides methods for creating and reading packets that adhere to this protocol. It's supposed to be used in conjunction with 🔧📻 LinkRawWireless.

Methods

Name	Return type	Description
`getChildrenData(response)`	LinkWirelessOpenSDK::ChildrenData	Parses the `response` and returns a struct containing all the received packets from the connected clients.
`getParentData(response)`	LinkWirelessOpenSDK::ParentData	Parses the `response` and returns a struct containing all the received packets from the host.
`createServerBuffer(fullPayload, fullPayloadSize, sequence, [targetSlots], [offset])`	LinkWirelessOpenSDK::SendBuffer<ServerSDKHeader>	Creates a buffer for the host to send a `fullPayload` with a valid header. If `fullPayloadSize` is higher than `84` (the maximum payload size), the buffer will only contain the first `84` bytes (unless an `offset` > 0 is used). A `sequence` number must be created by using `LinkWirelessOpenSDK::SequenceNumber::fromPacketId(...)`. Optionally, a `targetSlots` bit array can be used to exclude some clients from the transmissions (the default is `0b1111`).
`createServerACKBuffer(clientHeader, clientNumber)`	LinkWirelessOpenSDK::SendBuffer<ServerSDKHeader>	Creates a buffer for the host to acknowledge a header received from a certain `clientNumber`.
`createClientBuffer(fullPayload, fullPayloadSize, sequence, [offset])`	LinkWirelessOpenSDK::SendBuffer<ClientSDKHeader>	Creates a buffer for the client to send a `fullPayload` with a valid header. If `fullPayloadSize` is higher than `14` (the maximum payload size), the buffer will only contain the first `14` bytes (unless an `offset` > 0 is used). A `sequence` number must be created by using `LinkWirelessOpenSDK::SequenceNumber::fromPacketId(...)`.
`createClientACKBuffer(serverHeader)`	LinkWirelessOpenSDK::SendBuffer<ServerSDKHeader>	Creates a buffer for the client to acknowledge a header received from the host.

🌎 LinkUniversal

⬆️ A multiuse library that doesn't care whether you plug a Link Cable or a Wireless Adapter. It continuously switches between both and tries to connect to other peers, supporting the hot swapping of cables and adapters and all the features from 👾 LinkCable and 📻 LinkWireless.

https://github.com/afska/gba-link-connection/assets/1631752/d1f49a48-6b17-4954-99d6-d0b7586f5730

Constructor

new LinkUniversal(...) accepts these optional parameters:

Name	Type	Default	Description
`protocol`	LinkUniversal::Protocol	`AUTODETECT`	Specifies what protocol should be used (one of `LinkUniversal::Protocol::AUTODETECT`, `LinkUniversal::Protocol::CABLE`, `LinkUniversal::Protocol::WIRELESS_AUTO`, `LinkUniversal::Protocol::WIRELESS_SERVER`, or `LinkUniversal::Protocol::WIRELESS_CLIENT`).
`gameName`	const char*	`""`	The game name that will be broadcasted in wireless sessions (max `14` characters). The string must be a null-terminated character array. The library uses this to only connect to servers from the same game.
`cableOptions`	LinkUniversal::CableOptions	same as LinkCable	All the 👾 LinkCable constructor parameters in one struct.
`wirelessOptions`	LinkUniversal::WirelessOptions	same as LinkWireless	All the 📻 LinkWireless constructor parameters in one struct.
`randomSeed`	int	`123`	Random seed used for waits to prevent livelocks. If you use libtonc, pass `__qran_seed`.

You can also change these compile-time constants:

LINK_UNIVERSAL_MAX_PLAYERS: to set a maximum number of players. The default value is 5, but since LinkCable's limit is 4, you might want to decrease it.
LINK_UNIVERSAL_GAME_ID_FILTER: to restrict wireless connections to rooms with a specific game ID (0x0000 ~ 0x7fff). The default value (0) connects to any game ID and uses 0x7fff when serving.

Methods

The interface is the same as 👾 LinkCable. Additionally, it supports these methods:

Name	Return type	Description
`getState()`	LinkUniversal::State	Returns the current state (one of `LinkUniversal::State::INITIALIZING`, `LinkUniversal::State::WAITING`, or `LinkUniversal::State::CONNECTED`).
`getMode()`	LinkUniversal::Mode	Returns the active mode (one of `LinkUniversal::Mode::LINK_CABLE`, or `LinkUniversal::Mode::LINK_WIRELESS`).
`getProtocol()`	LinkUniversal::Protocol	Returns the active protocol (one of `LinkUniversal::Protocol::AUTODETECT`, `LinkUniversal::Protocol::CABLE`, `LinkUniversal::Protocol::WIRELESS_AUTO`, `LinkUniversal::Protocol::WIRELESS_SERVER`, or `LinkUniversal::Protocol::WIRELESS_CLIENT`).
`getWirelessState()`	LinkWireless::State	Returns the wireless state (same as 📻 LinkWireless's `getState()`).
`setProtocol(protocol)`	-	Sets the active `protocol`.

🔌 LinkGPIO

(aka General Purpose Mode)

⬆️ This is the default Link Port mode, and it allows users to manipulate pins SI, SO, SD and SC directly.

Methods

Name	Return type	Description
`reset()`	-	Resets communication mode to General Purpose (same as `Link::reset()`). Required to initialize the library!
`setMode(pin, direction)`	-	Configures a `pin` to use a `direction` (input or output).
`getMode(pin)`	LinkGPIO::Direction	Returns the direction set at `pin`.
`readPin(pin)`	bool	Returns whether a `pin` is HIGH or not (when set as an input).
`writePin(pin, isHigh)`	-	Sets a `pin` to be high or not (when set as an output).
`setSIInterrupts(isEnabled)`	-	If it `isEnabled`, an IRQ will be generated when `SI` changes from HIGH to LOW.

⚠️ always set the SI terminal to an input!

⚠️ call reset() when you finish doing GPIO stuff! (for compatibility with the other libraries)

🔗 LinkSPI

(aka Normal Mode)

⬆️ This is the GBA's implementation of SPI. You can use this to interact with other GBAs or computers that know SPI.

screenshot

Methods

Name	Return type	Description
`isActive()`	bool	Returns whether the library is active or not.
`activate(mode, [dataSize])`	-	Activates the library in a specific `mode` (one of `LinkSPI::Mode::SLAVE`, `LinkSPI::Mode::MASTER_256KBPS`, or `LinkSPI::Mode::MASTER_2MBPS`). By default, the `dataSize` is 32-bit, but can be changed to `LinkSPI::DataSize::SIZE_8BIT`.
`deactivate()`	-	Deactivates the library.
`transfer(data)`	u32	Exchanges `data` with the other end. Returns the received data.
`transfer(data, cancel)`	u32	Like `transfer(data)` but accepts a `cancel()` function. The library will continuously invoke it, and abort the transfer if it returns `true`.
`transferAsync(data, [cancel])`	-	Schedules a `data` transfer and returns. After this, call `getAsyncState()` and `getAsyncData()`. Note that until you retrieve the async data, normal `transfer(...)`s won't do anything!
`getAsyncState()`	LinkSPI::AsyncState	Returns the state of the last async transfer (one of `LinkSPI::AsyncState::IDLE`, `LinkSPI::AsyncState::WAITING`, or `LinkSPI::AsyncState::READY`).
`getAsyncData()`	u32	If the async state is `READY`, returns the remote data and switches the state back to `IDLE`. If not, returns an empty response.
`getMode()`	LinkSPI::Mode	Returns the current `mode`.
`getDataSize()`	LinkSPI::DataSize	Returns the current `dataSize`.
`setWaitModeActive(isActive)`	-	Enables or disables `waitMode` (*).
`isWaitModeActive()`	bool	Returns whether `waitMode` (*) is active or not.

(*) waitMode: The GBA adds an extra feature over SPI. When working as master, it can check whether the other terminal is ready to receive (ready: MISO=LOW), and wait if it's not (not ready: MISO=HIGH). That makes the connection more reliable, but it's not always supported on other hardware units (e.g. the Wireless Adapter), so it must be disabled in those cases.

waitMode is disabled by default.

MISO means SO on the slave side and SI on the master side.

⚠️ when using Normal Mode between two GBAs, use a GBC Link Cable!

⚠️ only use the 2Mbps mode with custom hardware (very short wires)!

⚠️ returns 0xFFFFFFFF (or 0xFF) on misuse or cancelled transfers!

SPI Configuration

The GBA operates using SPI mode 3 (CPOL=1, CPHA=1). Here's a connection diagram that illustrates how to connect a Link Cable to a Raspberry Pi 3's SPI pins:

⏱️ LinkUART

(aka UART Mode)

⬆️ This is the GBA's implementation of UART. You can use this to interact with a PC using a USB to UART cable. You can change the buffer size by setting the compile-time constant LINK_UART_QUEUE_SIZE.

Methods

Name	Return type	Description
`isActive()`	bool	Returns whether the library is active or not.
`activate(baudRate, dataSize, parity, useCTS)`	-	Activates the library using a specific UART mode. Defaults: 9600bps, 8-bit data, no parity bit, no CTS.
`deactivate()`	-	Deactivates the library.
`sendLine(string)`	-	Takes a null-terminated `string`, and sends it followed by a `'\n'` character. The null character is not sent.
`sendLine(data, cancel)`	-	Like `sendLine(string)` but accepts a `cancel()` function. The library will continuously invoke it, and abort the transfer if it returns `true`.
`readLine(string, [limit])`	bool	Reads characters into `string` until finding a `'\n'` character or a character `limit` is reached. A null terminator is added at the end. Returns `false` if the limit has been reached without finding a newline character.
`readLine(string, cancel, [limit])`	bool	Like `readLine(string, [limit])` but accepts a `cancel()` function. The library will continuously invoke it, and abort the transfer if it returns `true`.
`send(buffer, size, offset)`	-	Sends `size` bytes from `buffer`, starting at byte `offset`.
`read(buffer, size, offset)`	u32	Tries to read `size` bytes into `(u8*)(buffer + offset)`. Returns the number of read bytes.
`canRead()`	bool	Returns whether there are bytes to read or not.
`canSend()`	bool	Returns whether there is room to send new messages or not.
`availableForRead()`	u32	Returns the number of bytes available for read.
`availableForSend()`	u32	Returns the number of bytes available for send (buffer size - queued bytes).
`read()`	u8	Reads a byte. Returns 0 if nothing is found.
`send(data)`	-	Sends a `data` byte.

UART Configuration

The GBA operates using 1 stop bit, but everything else can be configured. By default, the library uses 8N1, which means 8-bit data and no parity bit. RTS/CTS is disabled by default.

diagram

Black wire (GND) -> GBA GND.
Green wire (TX) -> GBA SI.
White wire (RX) -> GBA SO.

🟪 LinkCube

(aka JOYBUS Mode)

⬆️ This is the GBA's implementation of JOYBUS, in which users connect the console to a GameCube (or Wii with GC ports) using an official adapter. The library can be tested using Dolphin/mGBA and gba-joybus-tester.

screenshot

You can change these compile-time constants:

LINK_CUBE_QUEUE_SIZE: to set a custom buffer size (how many incoming and outgoing values the queues can store at max). The default value is 10, which seems fine for most games.
- This affects how much memory is allocated. With the default value, it's around 120 bytes. There's a double-buffered pending queue (to avoid data races), and 1 outgoing queue.
- You can approximate the memory usage with:
  - LINK_CUBE_QUEUE_SIZE * sizeof(u32) * 3 <=> LINK_CUBE_QUEUE_SIZE * 12

Methods

Name	Return type	Description
`isActive()`	bool	Returns whether the library is active or not.
`activate()`	-	Activates the library.
`deactivate()`	-	Deactivates the library.
`wait()`	bool	Waits for data. Returns `true` on success, or `false` on JOYBUS reset.
`wait(cancel)`	bool	Like `wait()` but accepts a `cancel()` function. The library will invoke it after every SERIAL interrupt, and abort the wait if it returns `true`.
`canRead()`	bool	Returns `true` if there are pending received values to read.
`read()`	u32	Dequeues and returns the next received value. If there's no received data, a `0` will be returned.
`peek()`	u32	Returns the next received value without dequeuing it. If there's no received data, a `0` will be returned.
`send(data)`	-	Sends 32-bit `data`. If the other end asks for data at the same time you call this method, a `0x00000000` will be sent.
`pendingCount()`	u32	Returns the number of pending outgoing transfers.
`didReset([clear])`	bool	Returns whether a JOYBUS reset was requested or not. After this call, the reset flag is cleared if `clear` is `true` (default behavior).

📱 LinkMobile

(aka Mobile Adapter GB)

⬆️ This is a driver for an accessory that enables online conectivity on the GB and GBA. The protocol was reverse-engineered by the REON Team.

The original accessory was sold in Japan only and using it nowadays is hard since it relies on old tech, but REON has created an open-source implementation called libmobile, as well as support for emulators and microcontrollers.

It has two modes of operation:

Direct call (P2P): Calling someone directly for a 2-player session, using the other person's IP address or the phone number provided by the relay server.
ISP call (PPP): Calling an ISP number for internet access. In this mode, the adapter can open up to 2 TCP/UDP sockets and transfer arbitrary data.

screenshot

Constructor

new LinkMobile(...) accepts these optional parameters:

Name	Type	Default	Description
`timeout`	u32	`600`	Number of frames without completing a request to reset a connection.
`timerId`	u8 (0~3)	`3`	GBA Timer to use for sending.

You can update these values at any time without creating a new instance:

Call deactivate().
Mutate the config property.
Call activate().

You can also change these compile-time constants:

LINK_MOBILE_QUEUE_SIZE: to set a custom request queue size (how many commands can be queued at the same time). The default value is 10, which seems fine for most games.
- This affects how much memory is allocated. With the default value, it's around 3 KB.

Methods

All actions are asynchronous/nonblocking. That means, they will return true if nothing is awfully wrong, but the actual consequence will occur some frames later. You can call getState() at any time to know what it's doing.
On fatal errors, the library will transition to a NEEDS_RESET state. In that case, you can call getError() to know more details on what happened, and then activate() to restart.
When calling deactivate(), the adapter automatically turns itself off after 3 seconds of inactivity. However, to gracefully turn it off, it's recommended to call shutdown() first, wait until the state is SHUTDOWN, and then deactivate().

Name	Return type	Description
`isActive()`	bool	Returns whether the library is active or not.
`activate()`	-	Activates the library. After some time, if an adapter is connected, the state will be changed to `SESSION_ACTIVE`. If not, the state will be `NEEDS_RESET`, and you can retrieve the error with `getError()`.
`deactivate()`	-	Deactivates the library, resetting the serial mode to GPIO. Calling `shutdown()` first is recommended, but the adapter will put itself in sleep mode after 3 seconds anyway.
`shutdown()`	bool	Gracefully shuts down the adapter, closing all connections. After some time, the state will be changed to `SHUTDOWN`, and only then it's safe to call `deactivate()`.
`call(phoneNumber)`	bool	Initiates a P2P connection with a `phoneNumber`. After some time, the state will be `CALL_ESTABLISHED` (or `ACTIVE_SESSION` if the connection fails or ends). In REON/libmobile the phone number can be a number assigned by the relay server, or a 12-digit IPv4 address (for example, `"127000000001"` would be `127.0.0.1`).
`callISP(password, loginId)`	bool	Calls the ISP number registered in the adapter configuration, or a default number if the adapter hasn't been configured. Then, performs a login operation using the provided `password` and `loginId`. After some time, the state will be `PPP_ACTIVE`. If `loginId` is empty and the adapter has been configured, it will use the one stored in the configuration. Both parameters are null-terminated strings (max `32` characters).
`dnsQuery(domainName, result)`	bool	Looks up the IPv4 address for a `domainName` (a null-terminated string, max `253` characters). It also accepts an ASCII IPv4 address, converting it into a 4-byte address instead of querying the DNS server. The `result` is a pointer to a `LinkMobile::DNSQuery` struct that will be filled with the result. When the request is completed, the `completed` field will be `true`. If an IP address was found, the `success` field will be `true` and the `ipv4` field can be read as a 4-byte address.
`openConnection(ip, port, type, result)`	bool	Opens a TCP/UDP (`type`) connection at the given `ip` (4-byte address) on the given `port`. The `result` is a pointer to a `LinkMobile::OpenConn` struct that will be filled with the result. When the request is completed, the `completed` field will be `true`. If the connection was successful, the `success` field will be `true` and the `connectionId` field can be used when calling the `transfer(...)` method. Only `2` connections can be opened at the same time.
`closeConnection(connectionId, type, result)`	bool	Closes an active TCP/UDP (`type`) connection. The `result` is a pointer to a `LinkMobile::CloseConn` struct that will be filled with the result. When the request is completed, the `completed` field will be `true`. If the connection was closed correctly, the `success` field will be `true`.
`transfer(dataToSend, result, [connectionId])`	bool	Requests a data transfer (up to `254` bytes) and responds the received data. The transfer can be done with the other node in a P2P connection, or with any open TCP/UDP connection if a PPP session is active. In the case of a TCP/UDP connection, the `connectionId` must be provided. The `result` is a pointer to a `LinkMobile::DataTransfer` struct that will be filled with the received data. It can also point to `dataToSend` to reuse the struct. When the request is completed, the `completed` field will be `true`. If the transfer was successful, the `success` field will be `true`. If not, you can assume that the connection was closed.
`waitFor(asyncRequest)`	bool	Waits for `asyncRequest` to be completed. Returns `true` if the request was completed && successful, and the adapter session is still alive. Otherwise, it returns `false`. The `asyncRequest` is a pointer to a `LinkMobile::DNSQuery`, `LinkMobile::OpenConn`, `LinkMobile::CloseConn`, or `LinkMobile::DataTransfer`.
`hangUp()`	bool	Hangs up the current P2P or PPP call. Closes all connections.
`readConfiguration(configurationData)`	bool	Retrieves the adapter configuration, and puts it in the `configurationData` struct. If the adapter has an active session, the data is already loaded, so it's instantaneous.
`getState()`	LinkMobile::State	Returns the current state (one of `LinkMobile::State::NEEDS_RESET`, `LinkMobile::State::PINGING`, `LinkMobile::State::WAITING_TO_START`, `LinkMobile::State::STARTING_SESSION`, `LinkMobile::State::ACTIVATING_SIO32`, `LinkMobile::State::WAITING_32BIT_SWITCH`, `LinkMobile::State::READING_CONFIGURATION`, `LinkMobile::State::SESSION_ACTIVE`, `LinkMobile::State::CALL_REQUESTED`, `LinkMobile::State::CALLING`, `LinkMobile::State::CALL_ESTABLISHED`, `LinkMobile::State::ISP_CALL_REQUESTED`, `LinkMobile::State::ISP_CALLING`, `LinkMobile::State::PPP_LOGIN`, `LinkMobile::State::PPP_ACTIVE`, `LinkMobile::State::SHUTDOWN_REQUESTED`, `LinkMobile::State::ENDING_SESSION`, `LinkMobile::State::WAITING_8BIT_SWITCH`, or `LinkMobile::State::SHUTDOWN`).
`getRole()`	LinkMobile::Role	Returns the current role in the P2P connection (one of `LinkMobile::Role::NO_P2P_CONNECTION`, `LinkMobile::Role::CALLER`, or `LinkMobile::Role::RECEIVER`).
`isConfigurationValid()`	int	Returns whether the adapter has been configured or not. Returns `1` = yes, `0` = no, `-1` = unknown (no session active).
`isConnectedP2P()`	bool	Returns `true` if a P2P call is established (the state is `CALL_ESTABLISHED`).
`isConnectedPPP()`	bool	Returns `true` if a PPP session is active (the state is `PPP_ACTIVE`).
`isSessionActive()`	bool	Returns `true` if the session is active.
`canShutdown()`	bool	Returns `true` if there's an active session and there's no previous shutdown requests.
`getDataSize()`	LinkSPI::DataSize	Returns the current operation mode (`LinkSPI::DataSize`).
`getError()`	LinkMobile::Error	Returns details about the last error that caused the connection to be aborted.

🖱️ LinkPS2Mouse

⬆️ A PS/2 mouse driver for the GBA. Use it to add mouse support to your homebrew games. It's a straight port from this library.

Constructor

new LinkPS2Mouse(timerId), where timerId is the GBA Timer used for delays.

Methods

Name	Return type	Description
`isActive()`	bool	Returns whether the library is active or not.
`activate()`	-	Activates the library.
`deactivate()`	-	Deactivates the library.
`report(data[3])`	-	Fills the `data` int array with a report. The first int contains clicks that you can check against the bitmasks `LINK_PS2_MOUSE_LEFT_CLICK`, `LINK_PS2_MOUSE_MIDDLE_CLICK`, and `LINK_PS2_MOUSE_RIGHT_CLICK`. The second int is the X movement, and the third int is the Y movement.

⚠️ calling activate() or report(...) could freeze the system if nothing is connected: detecting timeouts using interrupts is the user's responsibility.

Pinout

 ____________
|PS/2 --- GBA|
|------------|
|CLOCK -> SI |
|DATA --> SO |
|VCC ---> VCC|
|GND ---> GND|

⌨️ LinkPS2Keyboard

⬆️ A PS/2 keyboard driver for the GBA. Use it to add keyboard support to your homebrew games.

Constructor

new LinkPS2Keyboard(onEvent), where onEvent is a function pointer that will receive the scan codes (u8). You should check a PS/2 scan code list online, but most common keys/events are included in enums like LINK_PS2_KEYBOARD_KEY::ENTER and LINK_PS2_KEYBOARD_EVENT::RELEASE.

Methods

Name	Return type	Description
`isActive()`	bool	Returns whether the library is active or not.
`activate()`	-	Activates the library.
`deactivate()`	-	Deactivates the library.

Pinout

 ____________
|PS/2 --- GBA|
|------------|
|CLOCK -> SI |
|DATA --> SO |
|VCC ---> VCC|
|GND ---> GND|