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.

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