mos-hardware 0.4.0

// copyright 2022 mikael lund aka wombat
//
// licensed under the apache license, version 2.0 (the "license");
// you may not use this file except in compliance with the license.
// you may obtain a copy of the license at
//
//     http://www.apache.org/licenses/license-2.0
//
// unless required by applicable law or agreed to in writing, software
// distributed under the license is distributed on an "as is" basis,
// without warranties or conditions of any kind, either express or implied.
// see the license for the specific language governing permissions and
// limitations under the license.

//! Registers for the MOS 6566/6567 (VIC-II) Chip
//!
//! The VIC-II (Video Interface Chip II), specifically known as the MOS Technology
//! 6567/8562/8564 (NTSC versions), 6569/8565/8566 (PAL), is the microchip tasked
//! with generating Y/C video signals (combined to composite video in the RF modulator)
//! and DRAM refresh signals in the Commodore 64 and C128 home computers.

use bitflags::bitflags;
use core::mem::size_of;
use static_assertions::const_assert;
use volatile_register::{RO, RW};

pub const BLACK: u8 = 0;
pub const WHITE: u8 = 1;
pub const RED: u8 = 2;
pub const CYAN: u8 = 3;
pub const PURPLE: u8 = 4;
pub const GREEN: u8 = 5;
pub const BLUE: u8 = 6;
pub const YELLOW: u8 = 7;
pub const ORANGE: u8 = 8;
pub const BROWN: u8 = 9;
pub const LIGHT_RED: u8 = 10;
pub const GRAY1: u8 = 11;
pub const GRAY2: u8 = 12;
pub const LIGHT_GREEN: u8 = 13;
pub const LIGHT_BLUE: u8 = 14;
pub const GRAY3: u8 = 15;

bitflags! {
    /// Bitmask for sprites 0 to 7.
    pub struct Sprites: u8 {
        const SPRITE0 = 0b00000001;
        const SPRITE1 = 0b00000010;
        const SPRITE2 = 0b00000100;
        const SPRITE3 = 0b00001000;
        const SPRITE4 = 0b00010000;
        const SPRITE5 = 0b00100000;
        const SPRITE6 = 0b01000000;
        const SPRITE7 = 0b10000000;
    }
}

impl Sprites {
    /// Construct from sprite index of bits
    ///
    /// # Examples
    /// ~~~
    /// const SPRITE2: Sprite = Sprites::new(2);
    /// ~~~
    pub const fn new(index: u8) -> Self {
        assert!(index < 8);
        match index {
            0 => Self::SPRITE0,
            1 => Self::SPRITE1,
            2 => Self::SPRITE2,
            3 => Self::SPRITE3,
            4 => Self::SPRITE4,
            5 => Self::SPRITE5,
            6 => Self::SPRITE6,
            7 => Self::SPRITE7,
            _ => panic!(),
        }
    }
}

bitflags! {
    /// Y-Scroll Register Mask (0xd011)
    pub struct ControlYFlags: u8 {
        /// Control smooth y scrolling
        const YSCROLL = 0b0000_0111;
        /// Switch between 25 (on) and 24 (off) row text mode
        const ROW_SELECT = 0b0000_1000;
        /// Blank screen to border color (0 = blank)
        const BLANK_SCREEN = 0b0001_0000;
        /// Enable bitmap mode (enable = 1)
        const BITMAP_MODE = 0b0010_0000;
        /// Extended color text mode (enable = 1)
        const EXTENDED_COLOR_MODE = 0b0100_0000;
        const RASTER_COMPARE = 0b1000_0000;
    }
}

bitflags! {
    /// X-Scroll Register Flags (0xD016)
    pub struct ControlXFlags: u8 {
        /// Control smooth x scrolling
        const XSCROLL = 0b0000_0111;
        /// Switch between 38 (off) or 40 (on) column text mode
        const COLUMN_SELECT = 0b0000_1000;
        /// Enable (on) multi color for text and bitmap modes
        const MULTICOLOR = 0b0001_0000;
        /// Should always be set to zero!
        const ALWAYS_ZERO = 0b0010_0000;
        /// Unused
        const UNUSED = 0b1100_0000;
    }
}

bitflags! {
    /// Interrupt Register Flags (0xD019).
    /// Bits are set to 1 when an IRQ is detected.
    pub struct InterruptFlags: u8 {
        /// Set when raster counter equals stored raster count
        const RASTER_COMPARE_IRQ = 0b00000001;
        /// Set for first collision of sprite with background
        const SPRITE_BACKGROUND_COLLISION = 0b00000010;
        /// Set for first collision of sprite with another sprite
        const SPRITE_SPRITE_COLLISION = 0b00000100;
        const LIGHPEN_TRIGGERED = 0b00001000;
        const ANY_IRQ = 0b10000000;
    }
}

bitflags! {
    /// Flags to trigger IRQ request when VIC-II interrupt
    /// conditions are met (0xD01A)
    pub struct IRQEnableFlags: u8 {
        const RASTER_COMPARE              = 0b0000_0001; // bit 0
        const SPRITE_BACKGROUND_COLLISION = 0b0000_0010; // bit 1
        const ENSPRITE_SPRITE_COLLISION   = 0b0000_0100; // bit 2
        const LIGHT_PEN                   = 0b0000_1000; // bit 3
    }
}

bitflags! {
    /// All possible charset memory locations
    ///
    /// # Examples
    /// ~~~
    /// let bank = vic2::ScreenBank::AT_2C00.bits() | vic2::CharsetBank::AT_2000.bits();
    /// (*c64::VIC).screen_and_charset_bank.write(bank);
    /// ~~~
    pub struct CharsetBank: u8 {
        const AT_0000 = 0b0000_0000;
        const AT_0800 = 0b0000_0010;
        const AT_1000 = 0b0000_0100;
        const AT_1800 = 0b0000_0110;
        const AT_2000 = 0b0000_1000;
        const AT_2800 = 0b0000_1010;
        const AT_3000 = 0b0000_1100;
        const AT_3800 = 0b0000_1110;
        const DEFAULT = Self::AT_1000.bits;
    }
}

impl CharsetBank {
    /// Generate bank from charset memory address. Will check if it is valid.
    ///
    /// # Examples
    /// ~~~
    /// const SCREEN: u16 = 0x2800;
    /// const CHARSET: u16 = 0x2000;
    /// const BANK: u8 = vic2::ScreenBank::from(SCREEN).bits() | vic2::CharsetBank::from(CHARSET).bits();
    /// ~~~
    pub const fn from(charset: u16) -> Self {
        let bank = ((charset >> 10) & 0x0e) as u8;
        Self::from_bits(bank).unwrap()
    }
}

bitflags! {
    /// All possible screen memory locations
    pub struct ScreenBank: u8 {
        const AT_0000 = 0b0000_0000;
        const AT_0400 = 0b0001_0000;
        const AT_0800 = 0b0010_0000;
        const AT_0C00 = 0b0011_0000;
        const AT_1000 = 0b0100_0000;
        const AT_1400 = 0b0101_0000;
        const AT_1800 = 0b0110_0000;
        const AT_1C00 = 0b0111_0000;
        const AT_2000 = 0b1000_0000;
        const AT_2400 = 0b1001_0000;
        const AT_2800 = 0b1010_0000;
        const AT_2C00 = 0b1011_0000;
        const AT_3000 = 0b1100_0000;
        const AT_3400 = 0b1101_0000;
        const AT_3800 = 0b1110_0000;
        const AT_3C00 = 0b1111_0000;
        const DEFAULT = Self::AT_0800.bits;
    }
}

impl ScreenBank {
    /// Generate bank from screen memory address. Will check if it is valid.
    ///
    /// # Examples
    /// ~~~
    /// const SCREEN: u16 = 0x2800;
    /// const CHARSET: u16 = 0x2000;
    /// const BANK: u8 = ScreenBank::from_address(SCREEN).bits() | ScreenBank::from_address(CHARSET).bits();
    /// ~~~
    pub const fn from_address(screen: u16) -> Self {
        let bank = (screen >> 6) as u8;
        Self::from_bits(bank).unwrap()
    }
}

/// X and Y positions for e.g. sprites
pub struct XYcoordinate {
    /// X position
    pub x: RW<u8>,
    /// Y position
    pub y: RW<u8>,
}

#[repr(C, packed)]
/// Hardware registers for the MOS Technologies Video Interface Controller II
pub struct MOSVideoInterfaceControllerII {
    /// Sprite positions (x0, y0, x1, ...)
    pub sprite_positions: [XYcoordinate; 8],
    /// `MSIGX` Most Significant Bits of Sprites 0-7 Horizontal Positions (0x10)
    ///
    /// Setting one of these bits to 1 adds 256 to the horizontal
    /// position of the corresponding sprite.
    /// Resetting one to 0 restricts the horizontal position of the
    /// corresponding sprite to a value of 255 or less.
    pub sprite_positions_most_significant_bit_of_x: RW<Sprites>,
    /// `SCROLY` Vertical Fine Scrolling and Control Register, 0x11
    pub control_y: RW<ControlYFlags>,
    /// `RASTER` Raster counter (0x12)
    ///
    /// This has two different functions, depending on whether reading or writing:
    /// 1. When _read_, it tells which screen line the electron beam is currently scanning.
    /// 2. _Writing_ to this register designates the comparison value for the Raster IRQ.
    pub raster_counter: RW<u8>,
    /// `LPENX` (0x13)
    pub lightpen_x: RW<u8>,
    /// `LPENY` (0x14)
    pub lightpen_y: RW<u8>,
    /// `SPENA` (0x15)
    pub sprite_enable: RW<Sprites>,
    /// Offset 0x16
    pub control_x: RW<ControlXFlags>,
    /// `YXPAND` (0x17)
    pub sprite_expand_y: RW<Sprites>,
    /// `VMCSB` Memory Control Register (0x18)
    pub screen_and_charset_bank: RW<u8>,
    /// `VICIRQ` Interrupt flag (0x19)
    ///
    /// The VIC-II chip is capable of generating a maskable request (IRQ)
    /// when certain conditions relating to the video display are fulfilled.
    pub irq_status: RW<InterruptFlags>,
    /// `IRQMSK` IRQ Mask Register (0x1a)
    pub irq_enable: RW<IRQEnableFlags>,
    /// `SPBGPR` Place sprites behind (0) in infront of bitmaps (0x1b)
    pub sprite_background_priority: RW<Sprites>,
    /// `SPMC` (0x1c)
    pub sprite_multicolor_mode: RW<Sprites>,
    /// Offset 0x1d
    pub sprite_expand_x: RW<Sprites>,
    /// Offset 0x1e
    pub sprite_sprite_collision: RO<Sprites>,
    /// Offset 0x1f
    pub sprite_background_collision: RO<Sprites>,
    /// Offset 0x20
    pub border_color: RW<u8>,
    /// Offset 0x21
    pub background_color0: RW<u8>,
    /// Offset 0x22
    pub background_color1: RW<u8>,
    /// Offset 0x23
    pub background_color2: RW<u8>,
    /// Offset 0x24
    pub background_color3: RW<u8>,
    /// Offset 0x25
    pub sprite_multicolor0: RW<u8>,
    /// Offset 0x26
    pub sprite_multicolor1: RW<u8>,
    /// `SPxCOL` Sprite Colors (0x2e)
    pub sprite_colors: [RW<u8>; 8],
}

const_assert!(size_of::<MOSVideoInterfaceControllerII>() == 0x2f);

impl MOSVideoInterfaceControllerII {
    /// Sets position of sprite identified by it's index
    pub fn set_sprite_pos(&self, index: u8, xpos: u8, ypos: u8) {
        unsafe {
            self.sprite_positions[index as usize].x.write(xpos);
            self.sprite_positions[index as usize].y.write(ypos);
        }
    }

    /// Sets color of sprite identified by it's index
    pub fn set_sprite_color(&self, index: u8, color: u8) {
        unsafe {
            self.sprite_colors[index as usize].write(color);
        }
    }
}

/// Calculate sprite pointer from pattern address
///
/// To make a given sprite show the pattern that's stored in RAM at `address`
/// (which must be divisible with 64), set the contents of the corresponding
/// sprite pointer address to `address` divided by 64. For instance, if the sprite pattern
/// begins at address 704, the pointer value will be 704 / 64 = 11.
///
/// # Examples
///
/// ~~~
/// const SPRITE_ADDRESS: u16 = 0x2000;
/// const SPRITE_PTR: u8 = to_sprite_pointer(SPRITE_ADDRESS);
/// ~~~
///
/// When called as `const`, assertions are done at compile time:
///
/// ~~~should_panic
/// const INVALID_SPRITE_ADDRESS: u16 = 0x2001; // compile time error
/// ~~~
///
/// # Image conversion
///
/// Image files can be converted using ImageMagick:
///
/// ~~~bash
/// convert image.png -alpha off -resize 24x21! -monochrome sprite.png
/// ~~~
///
/// and then converted into a byte array using Python:
///
/// ~~~python
/// import numpy as np
/// from PIL import Image
/// image = Image.open('sprite.png')
/// bits = (~np.asarray(image).reshape(int(24*21/8), 8))
/// for bits_in_byte in bits.astype(int):
///     print(int(''.join('01'[i] for i in bits_in_byte), 2), end=',')
/// ~~~
pub const fn to_sprite_pointer(address: u16) -> u8 {
    assert!(address % 64 == 0);
    assert!(address / 64 < 256);
    (address / 64) as u8
}