Technical Specifications

• Interupts and exceptions always switch to ARM, and should automatically switch back to Thumb on return
• Little endian by default
• You can only enter System mode from another privileged mode by modifying the mode bits of the Current Program Status Register (CPSR).
• Exceptions have a priority
• Exceptions/traps have normal and high vectors, that are controlled by external signals.
• 14 hardware interupts
• While ARM can be bi-endian, it appears the Game Boy Advance only supported little endian. This would probably make things easier in some ways.

Processor and memory

It uses a 32-bit ARM7TDMI processor, which is built on the ARM v4T architecture. It has 32KB of embedded RAM, 96KB of VRAM, and can address 256KB of RAM on the cartridge. The T in v4T means that the processor has two instruction sets. The ARM instruction set uses 32-bit word-aligned instructions, while the Thumb instruction set uses 16-bit halfword-aligned instructions.

Notes about Thumb: Both instruction sets follow the same execution path inside of the processor, and share a single implementation. Only the process of decoding the instructions is different between the two. Everything else is identical. The Thumb instruction set is useful when storing a program in an area of memory that only has a 16-bit bus width.

Display

The display has a resolution of 240x160 with a refresh rate of 59.73Hz. It uses a 15-bit color encoding (with 32,768 possible colors) and 5:5:5 chroma subsampling.

Sound

The sound hardware of the Game Boy Advance is really interesting, but I don't know enough to fill this section out all the way right now.