MagenTests

March 22, 2025 · View on GitHub

Collection of test roms to check and verify the behavior of the Gameboy (mostly Color) during the development of my emulator - MagenBoy

ColorBgOamPriority

The gameboy color has 3 different places where the priority between the Background layer and the OAM a layer can be declared.

This test verifies the reltions between those flags and the behavior when they colide.

Checkout the PanDocs for background on the CGB behavior.

You should see 5 green squares and 3 half grren and half blue squares with no red lines

Screnshoot from Orignal CGB hardware

Special thanks to ISSOtm for running this test rom on original hardware, verifying it actually works and screenshoting the result.

The gameboy color changes the way the PPU manages its internal OAM objects priority.

For more info checks the PanDocs.

You should see 2 pairs of rectangles connected or touching each other.

This peripheral was added in the GameBoy Color and the HBlank mode turns out to be a bit tricky.

For more info check the PanDocs.

One undocumented detail I found is that the HDMA HBlank should be halted when the CPU is halted.

The screen should be all green!

Errors

Red screen - HDMA HBlank operation have been executed succesfully
Blue screen - HDMA HBlank operation have been executed even tought the CPU is halted

This register is CGB only and controls the mode of the system, mainly for compatibality with old DMG carts.

This register is being writen by the bootrom and get locked after 0xFF50 is written to.

The screen should be all green!

When the PPU is off (LCDC bit 7 is clear) the mode reported by STAT should be set to HBLANK mode (0).

This test is valid for both DMG and CGB machines.

The screen should be all green! (White On DMG)

When attempting to access out of bounds RAM only the mapped address bits are being used (the high bits casuing the out of bounds will be ignored).

This test is valid for both DMG and CGB machines.

The screen should be all green! (White On DMG)