Hello world — plain C

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Two players move squares with the D-pad. This example uses devkitARM and a mode-3 bitmap, with no engine, font or graphics assets.

Build and run

Set the shared example key, then from the SDK root:

make -C examples/hello_world

Output: examples/hello_world/hello_world.gba. The Makefile uses DEVKITARM and DEVKITPRO, defaulting to the usual /opt/devkitpro installation if unset.

Load the same ROM on two consoles, each with a configured CanoFlash connected. The example probes the device automatically, opens a session and matchmakes into a public two-seat room with empty parameters. The master starts once both seats are occupied. See Loading.

Screen and controls

Display	Meaning
White bar moving across the top	Connection wait callback is running
Bar along the bottom	Waiting for the room to fill
One blinking square	Invalid configuration or no responding device
Two blinking squares	Session/room could not be opened
Three blinking squares	Link/session failed during play
Two moving squares	Local movement and received remote state

The D-pad moves your square. Error screens are terminal in this minimal example; reset after correcting the problem. It has no online exit menu.

Read the networking in order

cf_config_init() and cf_connect() open the session.
cf_room_init() and cf_matchmake() enter a room.
cf_poll() updates the waiting lobby; the master requests playing.
Each game frame polls once and queues the local position with cf_send().

The four-byte position struct contains signed 16-bit x/y coordinates. Only matching builds should exchange it. There is one remote participant, so this example does not need to route multiple sender slots.

Scope

The example demonstrates normal state transport and basic connection status. It does not implement reliable events, full state reconciliation or a complete reconnection interface. See Lobby for menus/codes and Reliable events for acknowledged application events.

An emulator can test rendering and startup, but requires real CanoFlash hardware for the network path.