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Updated NES hardware documentation

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Antonio Montes 2019-09-27 14:36:05 -07:00
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docs/stdlib/nes.md
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## nes_hardware
The `nes_hardware` module is imported automatically on NES targets.
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.
TODO
#### `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()`
Updates joypad1 by querying for new button 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 ax)`
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 a, byte x)`
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 a)`
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 a)`
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.
The `nes_mmc4` module is imported automatically on the NES MMC4 target
and contains routines related to MMC4 bankswitching.
#### `void set_prg_bank(byte a)`