nes.md

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NES/Famicom-oriented modules

nes_hardware

The nes_hardware module is imported automatically on NES targets. It contains defintions for the NES's memory-mapped registers, as well as some joypad and PPU management routines.

PPU memory-mapped registers

Named memory locations for interfacing with the PPU's memory-mapped registers.

Available variables:

• byte ppu_ctrl @$2000
• byte ppu_mask @$2001
• byte ppu_status @$2002
• byte oam_addr @$2003
• byte oam_data @$2004
• byte ppu_scroll @$2005
• byte ppu_addr @$2006
• byte ppu_data @$2007
• byte oam_dma @$4014

byte strobe_joypad()

Strobes joypads in preparation for reading new joypad states.

byte read_joypad1()

Get joypad1's state as a byte.

byte read_joypad2()

Get joypad2's state as a byte.

void simulate_reset()

Simulates a hardware reset by jumping to the reset vector, which then calls main().

void ppu_set_addr(word register(ax) address)

Sets the PPU to point at the VRAM address at ax, usually in preparation for a write via ppu_write_data().

byte read_ppu_status()

Gets the PPU status byte.

void ppu_set_scroll(byte register(a) xscroll, byte register(x) yscroll)

Sets the PPU scroll register. Parameter a defines the horizontal (X-axis) scroll value, and parameter x defines the vertical (Y-axis) scroll value.

void ppu_write_data(byte register(a) data)

Writes a byte to the PPU's VRAM at the address the PPU is currently pointing to. Usually used after a call to ppu_set_addr().

void ppu_oam_dma_write(byte register(a) page)

Initiates a DMA transfer of 256 bytes from CPU memory address $xx00-$xxFF to PPU OAM memory, where xx is the hexadecimal representation of parameter a.

nes_mmc4

The nes_mmc4 module is imported automatically on the NES MMC4 target and contains routines related to MMC4 bankswitching.

void set_prg_bank(byte register(a) bank)

Changes the $8000-$BFFF PRG bank.

void set_chr_bank0(byte register(a) bank)

Changes the CHR bank 0 ($0000-$0fff in the PPU memory space).

The high nibble (0 or 1) selects between chrrom0 and chrrom1 segments. The low nibble L (0-$F) selects a 4K-aligned address in the segment ($L000).

void set_chr_bank1(byte register(a) bank)

Changes the CHR bank 1 ($1000-$1fff in the PPU memory space).

The high nibble (0 or 1) selects between chrrom0 and chrrom1 segments. The low nibble L (0-$F) selects a 4K-aligned address in the segment ($L000).

void set_vertical_mirroring()

Switches nametable mirroring to vertical.

void set_horizontal_mirroring()

Switches nametable mirroring to horizontal.

nes_joy

Provides an interface for reading joypads that is compatible with the joy module.

alias input_a = input_btn

1 if A button pressed, 0 if not pressed.

byte input_b

1 if B button pressed, 0 if not pressed.

byte input_select

1 if Select button pressed, 0 if not pressed.

byte input_start

1 if Start button pressed, 0 if not pressed.

void read_joy1()

Reads the joypad from the port 1.

void read_joy2()

Reads the joypad from the port 2.

void read_also_joy1()

Reads the joypad from the port 1 and adds its readouts to the current readouts.

void read_also_joy2()

Reads the joypad from the port 2 and adds its readouts to the current readouts.

void nes_reset_joy()

alias reset_joy = nes_reset_joy!

Resets the state variables.

nes_joy1_default

Defines the joystick in port 1 as the default joystick.

alias read_joy = read_joy1