Handheld practices
Handhelds keep state in battery-backed RAM and real-time clocks. They connect to other units over link cables and infrared. Some read sensors. A reimplementation must reproduce these parts as well as the CPU. This page covers what every handheld project records beside the CPU state. Each family page covers its own hardware.
Saves and real-time clocks
The Game Boy's MBC3 mapper holds up to 2 MB of ROM, RAM and a real-time clock. The clock needs a 32.768 kHz crystal and a battery (Pan Docs: MBC3).
| Action | Address | Effect |
|---|---|---|
Write $08 to $0C | 4000 to 5FFF | Selects the RTC registers: seconds, minutes, hours, the low byte of the day counter, and DH |
Write $00 then $01 | 6000 to 7FFF | Latches the time |
DH holds day bit 8, a halt flag (bit 6) and a carry flag (bit 7). The day counter is 9 bits (0 to 511). Carry stays set until software clears it. Separate RTC accesses need about 4 µs between them. MBC30 (4 MiB ROM, 64 KiB RAM, with a timer) shipped only in the Japanese Pocket Monsters: Crystal Version. Other regions used MBC3 (Pan Docs: MBC3).
A save file with an RTC needs the clock state alongside the RAM. The clock state is the latched values, the halt flag and the carry flag. Tests can then reproduce time-based events, such as day and night or the daily events in the Pokémon Gold, Silver and Crystal games.
The Pokémon mini also has an RTC. It adds a shock sensor, IR for up to six players and rumble (Wikipedia: Pokémon mini).
Link cables and infrared
Link cables and infrared are more outside inputs.
- GBC infrared runs up to 9.5 kbit/s (Wikipedia: Game Boy Color).
- SGB games can read four joypads and run code on the SNES. Their timing differs between NTSC, PAL and the SGB2. Games that detect the SGB can retune their sound (Pan Docs: SGB Functions).
- The Game.com has a modem cartridge (Wikipedia: Game.com).
- BREW signs each downloaded game for one handset, so the game cannot be backed up (GameTechWiki: BREW).
Link-cable protocols are not covered here. Two examples are GBC serial at double speed and the Pokémon trade protocol.
Sensors and other inputs
- The Game.com has a touchscreen (Wikipedia: Game.com).
- The Gizmondo has GPS, GPRS and a camera (Wikipedia: Gizmondo).
- Switch 2 Game-Key Cards must stay inserted to launch. The Joy-Con 2 adds mouse input (Wikipedia: Nintendo Switch 2).
- Accelerometer cartridges such as Kirby Tilt 'n' Tumble on the GBC are commonly cited but not verified.
Add each of these to the list of outside inputs that a test records and replays (Inputs).
LCD behaviour
What a picture test compares depends on the LCD. Game & Watch graphics are fixed LCD segments. MAME draws them from SVG artwork (Wikipedia: Game & Watch; MAME hh_sm510.cpp). For segment games the parity test compares lit segments per frame (LCD games).
Some handheld games are reported to flicker sprites. They rely on slow LCD response (ghosting) to blend frames. Which games do this is not confirmed. For such a game, compare the raw output of each frame. Do any blending only in the presentation layer.