GBA

Bare Metal Programming
No Operating System
Makes C more obvious
GBA Reference
Simple Hardware
Understand performance tradeoffs
Von Neumann Architecture
- I/O
  - DMA
  - Button Controller
  - Video Controller
  - Audio Controller
- Memory
- Processor
RISC
Datatypes
- 8 bit char
- 16 bit short
- 32 int
32 bit address space

Memory Map

6 Display Modes
- Bit Mapped
- Tiled

Light Up a Pixel

Talk to device registers Screen is 240 columns, 160 rows REG_DISPCTL at 0x04000000 #define REG_DISPCTL *(volatile unsigned short int *) 0x04000000 Video Memory starts at 0x60000000 Turn on the pixel at row 5, column 8

offset = 5 * 240 + 8*
pixel5_8 = *(unsigned short *) 0X6000000 + offset)

Color

Type of unsigned short Note: BGR instead of RGB

Button Input

10 buttons, 1 bit per button, contained in button register(s). 0 → button down, 1 → button up

Graphics

HBlank and VBlank

If you are trying to change video memory while the system is rendering in vdraw, you get tearing. This is because you are changing the original instructions for what to draw (possibly) before they have actually finished executing. Instead, wait for vdraw, then wait for it to end, in order to wait for vblank. Then change video memory during vblank.

Graphics Loop

init
loop {
	prevState = currentState
	checkButtons()
	currentState = calculateCurrentState()
	waitForVBlank()
	undraw(prevState)
	draw(currentState)
}

Direct Memory Access

When drawing, for example, we have to copy from a source in memory to a buffer register and then into some destination location in memory. Therefore we have direct memory access (DMA) which allows us to directly move data in memory. It is a hardware feature that allows for faster moving of memory.

Font

2D arrays mapped to a table according to ASCII value.

Explorer

GBA