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146 lines
3.6 KiB
Markdown
146 lines
3.6 KiB
Markdown
[< back to index](../doc_index.md)
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# NES/Famicom-oriented modules
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## nes_hardware
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The `nes_hardware` module is imported automatically on NES targets.
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It contains defintions for the NES's memory-mapped registers, as well
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as some joypad and PPU management routines.
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#### `PPU memory-mapped registers`
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Named memory locations for interfacing with the PPU's memory-mapped registers.
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Available variables:
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* `byte ppu_ctrl @$2000`
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* `byte ppu_mask @$2001`
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* `byte ppu_status @$2002`
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* `byte oam_addr @$2003`
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* `byte oam_data @$2004`
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* `byte ppu_scroll @$2005`
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* `byte ppu_addr @$2006`
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* `byte ppu_data @$2007`
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* `byte oam_dma @$4014`
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#### `byte strobe_joypad()`
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Strobes joypads in preparation for reading new joypad states.
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#### `byte read_joypad1()`
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Get joypad1's state as a byte.
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#### `byte read_joypad2()`
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Get joypad2's state as a byte.
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#### `void simulate_reset()`
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Simulates a hardware reset by jumping to the reset vector,
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which then calls main().
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#### `void ppu_set_addr(word register(ax) address)`
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Sets the PPU to point at the VRAM address at ax, usually in preparation
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for a write via ppu_write_data().
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#### `byte read_ppu_status()`
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Gets the PPU status byte.
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#### `void ppu_set_scroll(byte register(a) xscroll, byte register(x) yscroll)`
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Sets the PPU scroll register. Parameter a defines the horizontal
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(X-axis) scroll value, and parameter x defines the vertical (Y-axis)
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scroll value.
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#### `void ppu_write_data(byte register(a) data)`
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Writes a byte to the PPU's VRAM at the address the PPU
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is currently pointing to. Usually used after a call to ppu_set_addr().
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#### `void ppu_oam_dma_write(byte register(a) page)`
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Initiates a DMA transfer of 256 bytes from CPU memory address $xx00-$xxFF
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to PPU OAM memory, where xx is the hexadecimal representation of parameter a.
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## nes_mmc4
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The `nes_mmc4` module is imported automatically on the NES MMC4 target
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and contains routines related to MMC4 bankswitching.
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#### `void set_prg_bank(byte register(a) bank)`
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Changes the $8000-$BFFF PRG bank.
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#### `void set_chr_bank0(byte register(a) bank)`
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Changes the CHR bank 0 ($0000-$0fff in the PPU memory space).
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The high nibble (0 or 1) selects between `chrrom0` and `chrrom1` segments.
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The low nibble L (0-$F) selects a 4K-aligned address in the segment ($L000).
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#### `void set_chr_bank1(byte register(a) bank)`
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Changes the CHR bank 1 ($1000-$1fff in the PPU memory space).
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The high nibble (0 or 1) selects between `chrrom0` and `chrrom1` segments.
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The low nibble L (0-$F) selects a 4K-aligned address in the segment ($L000).
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#### `void set_vertical_mirroring()`
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Switches nametable mirroring to vertical.
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#### `void set_horizontal_mirroring()`
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Switches nametable mirroring to horizontal.
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## nes_joy
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Provides an interface for reading joypads that is compatible with the [`joy` module](./joy.md).
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#### `alias input_a = input_btn`
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1 if A button pressed, 0 id not pressed.
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#### `byte input_b`
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1 if B button pressed, 0 id not pressed.
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#### `byte input_select`
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1 if Select button pressed, 0 id not pressed.
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#### `byte input_start`
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1 if Start button pressed, 0 id not pressed.
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#### `void read_joy1()`
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Reads the joypad from the port 1.
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#### `void read_joy2()`
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Reads the joypad from the port 2.
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#### `void read_also_joy1()`
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Reads the joypad from the port 1 and adds its readouts to the current readouts.
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#### `void read_also_joy2()`
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Reads the joypad from the port 2 and adds its readouts to the current readouts.
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#### `void nes_reset_joy()`
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#### `alias reset_joy = nes_reset_joy!`
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Resets the state variables.
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## nes_joy1_default
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Defines the joystick in port 1 as the default joystick.
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#### `alias read_joy = read_joy1`
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