// Rewritten from https://github.com/BigEvilCorporation/megadrive_samples/blob/313e16db9c8cdd0bcd0c98223b3d4245f921b31d/3_sprites/sprites.asm

//==============================================================
// SEGA MEGA DRIVE/GENESIS - DEMO 3 - SPRITES SAMPLE
//==============================================================
// by Big Evil Corporation
//==============================================================

// A small, discreet, and complete sprites sample, with a healthy
// dose of comments and explanations for beginners.
// Runs on genuine hardware, and (hopefully) all emulators.
//
// I recommend reading and understanding the Scroll Planes
// sample first.
//
// To assemble this program with ASM68K.EXE:
//    ASM68K.EXE /p sprites.asm,sprites.bin,sprites.map,sprites.lst
//
// To assemble this program with SNASM68K.EXE:
//    SNASM68K.EXE /p sprites.asm,sprites.map,sprites.lst,sprites.bin
//
// sprites.asm = this source file
// sprites.bin = the binary file, fire this up in your emulator!
// sprites.lst = listing file, shows assembled addresses alongside
//               your source code, open in a text editor
// sprites.map = symbol map file for linking (unused)

//==============================================================

#include <stdint.h>
#include <stddef.h>

//==============================================================
// CONSTANTS
//==============================================================

// VDP port addresses
#define VDP_DATA                ((volatile uint16_t*)0x00C00000L)
#define VDP_CONTROL             ((volatile uint16_t*)0x00C00004L)

// VDP commands
#define VDP_CMD_VRAM_WRITE      ((uint32_t)0x40000000L)
#define VDP_CMD_CRAM_WRITE      ((uint32_t)0xC0000000L)
#define VDP_CMD_VSRAM_WRITE     ((uint32_t)0x40000010L)

// VDP memory addresses
// according to VDP registers 0x2, 0x4, and 0xD (see table above)
#define VRAM_ADDR_TILES         (0x0000)
#define VRAM_ADDR_PLANE_A       (0xC000)
#define VRAM_ADDR_PLANE_B       (0xE000)
#define VRAM_ADDR_SPRITE_TABLE  (0xF000) // NEW in this demo - the Sprite Attribute Table (SAT)
#define VRAM_ADDR_HSCROLL       (0xFC00)

// Screen width and height (in pixels)
#define VDP_SCREEN_WIDTH        (0x0140)
#define VDP_SCREEN_HEIGHT       (0x00F0)

// The plane width and height (in tiles)
// according to VDP register 0x10 (see table above)
#define VDP_PLANE_WIDTH         (0x40)
#define VDP_PLANE_HEIGHT        (0x20)

// The size of the sprite plane (512x512 pixels)
//
// With only a 320x240 display size, a lot of this
// is off screen, which is useful for hiding sprites
// when not needed (saves needing to adjust the linked
// list in the attribute table).
#define VDP_SPRITE_PLANE_WIDTH  (0x0200)
#define VDP_SPRITE_PLANE_HEIGHT (0x0200)

// The sprite border (invisible area left + top) size
//
// The sprite plane is 512x512 pixels, but is offset by
// -128 pixels in both X and Y directions. To see a sprite
// on screen at 0,0 we need to offset its position by
// this border.
#define VDP_SPRITE_BORDER_X     (0x80)
#define VDP_SPRITE_BORDER_Y     (0x80)

// Hardware version address
#define HARDWARE_VER_ADDRESS    ((uint8_t*)0x00A10001L)

// TMSS
#define TMSS_ADDRESS            ((uint32_t*)0x00A14000L)
#define TMSS_SIGNATURE          (('S' << 24) | ('E' << 16) | ('G' << 8) | 'A')

// The size of a word and longword
#define SIZE_WORD               (2)
#define SIZE_LONG               (4)

// The size of one palette (in bytes, words, and longwords)
#define SIZE_PALETTE_B          (0x20)
#define SIZE_PALETTE_W          (SIZE_PALETTE_B/SIZE_WORD)
#define SIZE_PALETTE_L          (SIZE_PALETTE_B/SIZE_LONG)

// The size of one graphics tile (in bytes, words, and longwords)
#define SIZE_TILE_B             (0x20)
#define SIZE_TILE_W             (SIZE_TILE_B/SIZE_WORD)
#define SIZE_TILE_L             (SIZE_TILE_B/SIZE_LONG)

// Text draw position (in tiles)
#define TEXT_POS_X              (0x02)
#define TEXT_POS_Y              (0x04)

// Sprite initial draw positions (in pixels)
#define SPRITE_1_START_POS_X    (VDP_SPRITE_BORDER_X)
#define SPRITE_1_START_POS_Y    (VDP_SPRITE_BORDER_Y)
#define SPRITE_2_START_POS_X    (VDP_SPRITE_BORDER_X + 0x0040)
#define SPRITE_2_START_POS_Y    (VDP_SPRITE_BORDER_Y + 0x0020)

// Speed (in pixels per frame) to move our sprites
#define SPRITE_1_MOVE_SPEED_X   (0x1)
#define SPRITE_1_MOVE_SPEED_Y   (0x1)
#define SPRITE_2_MOVE_SPEED_X   (0x2)
#define SPRITE_2_MOVE_SPEED_Y   (0x0)

//==============================================================
// MEMORY MAP
//==============================================================
// We need to store the current sprite positions in RAM and update
// them each frame. There are a few ways to create a memory map,
// but the cleanest, simplest, and easiest to maintain method
// uses the assembler's "RS" keywords. RSSET begins a new table of
// offsets starting from any other offset (here we're starting at
// 0x00FF0000, the start of RAM), and allows us to add named entries
// of any size for the "variables". We can then read/write these
// variables using the offsets' labels (see INT_VInterrupt for use
// cases).
//==============================================================
#define RAM_SPRITE_1_POS_X      ((uint16_t*)0x00FF0000) // 1 table entry of word size for sprite 1's X pos
#define RAM_SPRITE_1_POS_Y      ((uint16_t*)0x00FF0002) // 1 table entry of word size for sprite 1's Y pos
#define RAM_SPRITE_2_POS_X      ((uint16_t*)0x00FF0004) // 1 table entry of word size for sprite 2's X pos
#define RAM_SPRITE_2_POS_Y      ((uint16_t*)0x00FF0006) // 1 table entry of word size for sprite 2's Y pos

// !! Be careful when adding any table entries of BYTE size, since
// you'll need to start worrying about alignment. More of this in a
// future demo.

// Number of palettes to write to CRAM
#define PALETTE_COUNT (0x2)

//==============================================================
// TILE IDs
//==============================================================
// The indices of the first tile in each sprite. We only need
// to tell the sprite table where to find the starting tile of
// each sprite, so we don't bother keeping track of every tile
// index.
//
// Note we still leave the first tile blank (planes A and B are
// filled with tile 0) so we'll be uploading our sprite tiles
// from index 1.
//
// See bottom of the file for the sprite tiles themselves.
//==============================================================
#define TILE_ID_BLANK       (0x00) // The blank tile at index 0
#define TILE_ID_SPRITE_1    (0x01) // Sprite 1 index (4 tiles)
#define TILE_ID_SPRITE_2    (0x05) // Sprite 2 index (12 tiles)

// Total number of tiles in the sprites to upload to VRAM
#define TILE_COUNT          (0x11) // Total tiles = 16

//==============================================================
// INITIAL VDP REGISTER VALUES
//==============================================================
// In this demo, we're particularly interested in register 0x5,
// which specifies the address of the Sprite Attribute Table
// (SAT) within VRAM. Here it's set to 0xF000.
//==============================================================
static const uint8_t vdp_registers[] = {
    0x14, // 0x00: H interrupt on, palettes on
    0x74, // 0x01: V interrupt on, display on, DMA on, Genesis mode on
    0x30, // 0x02: Pattern table for Scroll Plane A at VRAM 0xC000 (bits 3-5 = bits 13-15)
    0x00, // 0x03: Pattern table for Window Plane at VRAM 0x0000 (disabled) (bits 1-5 = bits 11-15)
    0x07, // 0x04: Pattern table for Scroll Plane B at VRAM 0xE000 (bits 0-2 = bits 11-15)
    0x78, // 0x05: Sprite Attribute Table at VRAM 0xF000 (bits 0-6 = bits 9-15)
    0x00, // 0x06: Unused
    0x00, // 0x07: Background colour: bits 0-3 = colour, bits 4-5 = palette
    0x00, // 0x08: Unused
    0x00, // 0x09: Unused
    0x08, // 0x0A: Frequency of Horiz. interrupt in Rasters (number of lines travelled by the beam)
    0x00, // 0x0B: External interrupts off, V scroll per-page, H scroll per-page
    0x81, // 0x0C: Shadows and highlights off, interlace off, H40 mode (320 x 224 screen res)
    0x3F, // 0x0D: Horiz. scroll table at VRAM 0xFC00 (bits 0-5)
    0x00, // 0x0E: Unused
    0x02, // 0x0F: Autoincrement 2 bytes
    0x01, // 0x10: Scroll plane size: 64x32 tiles
    0x00, // 0x11: Window Plane X pos 0 left (pos in bits 0-4, left/right in bit 7)
    0x00, // 0x12: Window Plane Y pos 0 up (pos in bits 0-4, up/down in bit 7)
    0xFF, // 0x13: DMA length lo byte
    0xFF, // 0x14: DMA length hi byte
    0x00, // 0x15: DMA source address lo byte
    0x00, // 0x16: DMA source address mid byte
    0x80, // 0x17: DMA source address hi byte, memory-to-VRAM mode (bits 6-7)
};

//==============================================================
// PALETTE
//==============================================================
// In this demo we'll be using one palette per sprite,
// so we've added a palette count to upload the correct number
// of entries.
//==============================================================

static const uint16_t palette[SIZE_PALETTE_W * PALETTE_COUNT] = {
    // Palette for sprite 1
    0x0000,
    0x0020,
    0x0EEE,
    0x00AC,
    0x02EA,
    0x00EE,
    0x0008,
    0x000C,
    0x000A,
    0x0000,
    0x0000,
    0x0000,
    0x0000,
    0x0000,
    0x0000,
    0x0000,
    // Palette for sprite 2
    0x0000,
    0x0004,
    0x0226,
    0x0040,
    0x0446,
    0x0262,
    0x0662,
    0x004A,
    0x0468,
    0x0882,
    0x006C,
    0x0202,
    0x04A0,
    0x0AC2,
    0x06AE,
    0x02EC,
};

//==============================================================
// SPRITE TILES
//==============================================================
// The sprite graphics tiles. Too big to paste in here, so we'll
// include them from external files at the bottom of the ROM.
//
// If your tile data is in binary format rather than text, use
// INCBIN instead of INCLUDE.
//==============================================================

extern const uint32_t sprite_tiles[TILE_COUNT * SIZE_TILE_L];

//==============================================================
// VRAM WRITE MACROS
//==============================================================
// Some utility macros to help generate addresses and commands for
// writing data to video memory, since they're tricky (and
// error prone) to calculate manually.
// The resulting command and address is written to the VDP's
// control port, ready to accept data in the data port.
//==============================================================

// Set the VRAM (video RAM) address to write to next
static inline void SetVRAMWrite(uint16_t addr)
{
    *(volatile uint32_t*)VDP_CONTROL = VDP_CMD_VRAM_WRITE | ((addr & 0x3FFF) << 16) | (addr >> 14);
}

// Set the CRAM (colour RAM) address to write to next
static inline void SetCRAMWrite(uint16_t addr)
{
    *(volatile uint32_t*)VDP_CONTROL = VDP_CMD_CRAM_WRITE | ((addr & 0x3FFF) << 16) | (addr >> 14);
}

// Set the VSRAM (vertical scroll RAM) address to write to next
static inline void SetVSRAMWrite(uint16_t addr)
{
    *(volatile uint32_t*)VDP_CONTROL = VDP_CMD_VSRAM_WRITE | ((addr & 0x3FFF) << 16) | (addr >> 14);
}

//==============================================================
// SPRITE ATTRIBUTE MACRO
//==============================================================
// A macro to help build an entry in the Sprite Attribute
// Table, since manipulating structures and bit twiddling isn't
// the focus of this demo, and would make the code harder to
// read.
//==============================================================
// Proper game implementations would make use of a local SAT
// table in RAM and use DMA to transfer the table to VRAM each
// frame (which also allows us to use RAM like a "stream" to write
// this data more efficiently) but this is the best method for
// teaching the basics first.
//==============================================================
// Each sprite attribute entry is in the following format:
//
//   Y coordinate      1 word - the Y coordinate on the sprite plane
//   Dimensions bits   1 byte - bits describing the layout (1x1 tiles up to 4x4 tiles)
//   Linked list next  1 byte - the index of the next sprite to draw, or 0 if end of list
//   Prio/palette/flip 1 byte - the priority (bit 15), palette (bits 14-13),
//                              v/h flip (bits 12 and 11), and top 3 bits of the tile ID
//   Tile ID bottom    1 byte - the bottom 8 bits of the tile ID
//   X coordinate      1 word - the X coordinate on the sprite plane
//==============================================================

// Writes a sprite attribute structure to 4 registers, ready to write to VRAM
static struct SpriteStructure { uint16_t reg1, reg2, reg3, reg4; } BuildSpriteStructure(
        uint16_t x_pos,          // X pos on sprite plane
        uint16_t y_pos,          // Y pos on sprite plane
        uint16_t dimension_bits, // Sprite tile dimensions (4 bits)
        uint16_t next_id,        // Next sprite index in linked list
        uint16_t priority_bit,   // Draw priority
        uint16_t palette_id,     // Palette index
        uint16_t flip_x,         // Flip horizontally
        uint16_t flip_y,         // Flip vertically
        uint16_t tile_id)        // First tile index
{
    return (struct SpriteStructure){
        .reg1 = y_pos,
        .reg2 = (dimension_bits << 8) | next_id,
        .reg3 = (priority_bit << 14) | (palette_id << 13) | (flip_x << 11) | (flip_y << 10) |
            tile_id,
        .reg4 = x_pos,
    };
}

static void VDP_WriteTMSS(void)
{
    // The TMSS (Trademark Security System) locks up the VDP if we don't
    // write the string 'SEGA' to a special address. This was to discourage
    // unlicensed developers, since doing this displays the "LICENSED BY SEGA
    // ENTERPRISES LTD" message to screen (on Mega Drive models 1 and higher).
    //
    // First, we need to check if we're running on a model 1+, then write
    // 'SEGA' to hardware address 0xA14000.
    const uint8_t ver = (*HARDWARE_VER_ADDRESS) & 0x0f;
    if (ver != 0) {
        *TMSS_ADDRESS = TMSS_SIGNATURE;
    }

    // Check VDP
    // Read VDP status register (hangs if no access)
    *VDP_CONTROL;
}

static void VDP_LoadRegisters(void)
{
    // To initialise the VDP, we write all of its initial register values from
    // the table at the top of the file, using a loop.
    //
    // To write a register, we write a word to the control port.
    // The top bit must be set to 1 (so 0x8000), bits 8-12 specify the register
    // number to write to, and the bottom byte is the value to set.
    //
    // In binary:
    //   100X XXXX YYYY YYYY
    //   X = register number
    //   Y = value to write

    // Set VDP registers
    for (size_t i = 0; i < sizeof(vdp_registers) / sizeof(*vdp_registers); i++) {
        const uint16_t cmd = 0x8000; // 'Set register 0' command
        const uint16_t reg_num = i << 8;
        *VDP_CONTROL = cmd | reg_num | vdp_registers[i];
    }
}

int main(void)
{
    //==============================================================
    // Initialise the Mega Drive
    //==============================================================

    // Write the TMSS signature (if a model 1+ Mega Drive)
    VDP_WriteTMSS();

    // Load the initial VDP registers
    VDP_LoadRegisters();

    //==============================================================
    // Clear VRAM (video memory)
    //==============================================================

    // Setup the VDP to write to VRAM address 0x0000 (start of VRAM)
    SetVRAMWrite(0x0000);

    // Write 0's across all of VRAM
    const size_t count = (0x00010000 / SIZE_WORD); // Loop counter = 64kb, in words
    for (size_t i = 0; i < count; i++) {
        *VDP_DATA = 0x0; // Write a 0x0000 (word size) to VRAM
    }

    //==============================================================
    // Write the palette to CRAM (colour memory)
    //==============================================================

    // Setup the VDP to write to CRAM address 0x0000 (first palette)
    SetCRAMWrite(0x0000);

    // Write the palettes to CRAM
    //
    // This time we're writing multiple palettes, so multiply the word count
    // by the palette count (and don't forget the -1 for the loop counter).
    for (size_t i = 0; i < PALETTE_COUNT * SIZE_PALETTE_W; i++) {
        *VDP_DATA = palette[i]; // Write palette entry
    }

    //==============================================================
    // Write the sprite tiles to VRAM
    //==============================================================

    // Setup the VDP to write to VRAM address 0x0020 (the address of the first sprite tile, index 1)
    //
    // We need to leave the first tile blank (we cleared VRAM, so it should be all 0's) for
    // planes A and B to display, so skip the first tile (offset address by size_tile_b).
    SetVRAMWrite(VRAM_ADDR_TILES + SIZE_TILE_B);

    // Write the font glyph tiles to VRAM
    for (size_t i = 0; i < TILE_COUNT * SIZE_TILE_L; i++) {
        // Write tile line (4 bytes per line), and post-increment address
        *(volatile uint32_t*)VDP_DATA = sprite_tiles[i];
    }

    //==============================================================
    // Set up the Sprite Attribute Table (SAT)
    //==============================================================

    // The Sprite Attribute Table is a table of sprites to draw.
    // Each entry in the table describes the first tile ID, the number
    // of tiles to draw (and their layout), the X and Y position
    // (on the 512x512 sprite plane), the palette to draw with, a
    // priority flag, and X/Y flipping flags.
    //
    // Sprites can be layed out in these tile dimensions:
    //
    // 1x1 (1 tile)  - 0000
    // 1x2 (2 tiles) - 0001
    // 1x3 (3 tiles) - 0010
    // 1x4 (4 tiles) - 0011
    // 2x1 (2 tiles) - 0100
    // 2x2 (4 tiles) - 0101
    // 2x3 (6 tiles) - 0110
    // 2x4 (8 tiles) - 0111
    // 3x1 (3 tiles) - 1000
    // 3x2 (6 tiles) - 1001
    // 3x3 (9 tiles) - 1010
    // 3x4 (12 tiles)- 1011
    // 4x1 (4 tiles) - 1100
    // 4x2 (8 tiles) - 1101
    // 4x3 (12 tiles)- 1110
    // 4x4 (16 tiles)- 1111
    //
    // The tiles are layed out in COLUMN MAJOR, rather than planes A and B
    // which are row major. Tiles within a sprite cannot be reused (since it
    // only accepts a starting tile and a count/layout) so the whole sprite
    // needs uploading to VRAM in one consecutive chunk, even if some tiles
    // are duplicates.
    //
    // The X/Y flipping flags take the layout into account, you don't need
    // to re-adjust the layout, position, or tile IDs to flip the entire
    // sprite as a whole.
    //
    // There are 64 entries in the table, but the number of them drawn,
    // and the order in which they're processed, is determined by a linked
    // list. Each sprite entry has an index to the NEXT sprite to be drawn.
    // If this index is 0, the list ends, and the VDP won't draw any more
    // sprites this frame.

    // Start writing to the sprite attribute table in VRAM
    SetVRAMWrite(VRAM_ADDR_SPRITE_TABLE);

    //==============================================================
    // Set up sprite 1

    // Write all values into registers first to make it easier. We
    // write to VRAM one word at a time (auto-increment is set to 2
    // in VDP register 0xF), so we'll assign each word to a register.
    //
    // Since bit twiddling and manipulating structures isn't the focus of
    // this sample, we have a macro to simplify this part.

    // Position:   sprite_1_start_pos_x,sprite_1_start_pos_y
    // Dimensions: 2x2 tiles (8 tiles total) = 0101 in binary (see table above)
    // Next link:  sprite index 1 is next to be processed
    // Priority:   0
    // Palette id: 0
    // Flip X:     0
    // Flip Y:     0
    // Tile id:    tile_id_sprite_1
    const struct SpriteStructure sprite1 = BuildSpriteStructure(
            SPRITE_1_START_POS_X, SPRITE_1_START_POS_Y, 5, 1, 0, 0, 0, 0, TILE_ID_SPRITE_1);

    // Write the entire sprite attribute structure to the sprite table
    *VDP_DATA = sprite1.reg1;
    *VDP_DATA = sprite1.reg2;
    *VDP_DATA = sprite1.reg3;
    *VDP_DATA = sprite1.reg4;

    //==============================================================
    // Set up sprite 2

    // Position:   sprite_2_start_pos_x,sprite_2_start_pos_y
    // Dimensions: 4x3 tiles (16 tiles total) = 1110 in binary (see table above)
    // Next link:  sprite index 0 (end of linked list)
    // Priority:   0
    // Palette id: 1
    // Flip X:     0
    // Flip Y:     0
    // Tile id:    tile_id_sprite_2
    const struct SpriteStructure sprite2 = BuildSpriteStructure(
            SPRITE_2_START_POS_X, SPRITE_2_START_POS_Y, 0xe, 0, 0, 1, 0, 0, TILE_ID_SPRITE_2);

    // Write the entire sprite attribute structure to the sprite table
    *VDP_DATA = sprite2.reg1;
    *VDP_DATA = sprite2.reg2;
    *VDP_DATA = sprite2.reg3;
    *VDP_DATA = sprite2.reg4;

    //==============================================================
    // Intitialise variables in RAM
    //==============================================================
    *RAM_SPRITE_1_POS_X = SPRITE_1_START_POS_X;
    *RAM_SPRITE_1_POS_Y = SPRITE_1_START_POS_Y;
    *RAM_SPRITE_2_POS_X = SPRITE_2_START_POS_X;
    *RAM_SPRITE_2_POS_Y = SPRITE_2_START_POS_Y;

    //==============================================================
    // Initialise status register and set interrupt level.
    // This begins firing vertical and horizontal interrupts.
    //
    // Since the vinterrupt does something meaningful in this
    // demo, we start this AFTER setting up the VDP to draw and
    // intialising the variables in RAM.
    //==============================================================
    asm inline volatile ("  move.w #0x2300, %sr");

    // Finished!

    //==============================================================
    // Loop forever
    //==============================================================
    // This loops forever, effectively ending our main routine,
    // but the VDP will continue to run of its own accord and
    // will still fire vertical and horizontal interrupts (which is
    // where our update code is), so the demo continues to run.
    //
    // For a game, it would be better to use this loop for processing
    // input and game code, and wait here until next vblank before
    // looping again. We only use vinterrupt for updates in this demo
    // for simplicity (because we don't yet have any timing code).
    while (1);
}

//==============================================================
// CODE ENTRY POINT
//==============================================================
// The "main()" function. Your code starts here. Once the CPU
// has finished initialising, it will jump to this entry point
// (specified in the vector table at the top of the file).
//==============================================================
__attribute__((interrupt)) void CPU_EntryPoint(void)
{
    main();
}

// Vertical interrupt - run once per frame (50hz in PAL, 60hz in NTSC)
__attribute__((interrupt)) void INT_VInterrupt(void)
{
    // Fetch current sprite coordinates from RAM
    //
    // Animate them (x/y coords are 9 bits, so this
    // wraps around the whole 512x512 sprite plane)
    //
    // Store updated values back in RAM for next frame
    *RAM_SPRITE_1_POS_X += SPRITE_1_MOVE_SPEED_X;
    *RAM_SPRITE_1_POS_Y += SPRITE_1_MOVE_SPEED_Y;
    *RAM_SPRITE_2_POS_X += SPRITE_2_MOVE_SPEED_X;
    *RAM_SPRITE_2_POS_Y += SPRITE_2_MOVE_SPEED_Y;

    // Write updated coordinates to the Sprite Attribute Table in VRAM.
    // Each entry is 8 bytes in size, so sprite 1 is at table+0x0000,
    // and sprite 2 is at table+0x0008.
    //
    // The Y coord is the 1st word in the structure, and the X coord is
    // the 4th. As already noted, there are cleaner ways to do this,
    // like storing the tables in RAM and copying them via DMA every
    // frame, but that's beyond the focus of this sample.

    // Sprite 1's Y coordinate is at table+0x0000
    SetVRAMWrite(VRAM_ADDR_SPRITE_TABLE + 0x0000);
    *VDP_DATA = *RAM_SPRITE_1_POS_Y;

    // Sprite 1's X coordinate is at table+0x0006
    SetVRAMWrite(VRAM_ADDR_SPRITE_TABLE + 0x0006);
    *VDP_DATA = *RAM_SPRITE_1_POS_X;

    // Sprite 2's Y coordinate is at table+0x0008
    SetVRAMWrite(VRAM_ADDR_SPRITE_TABLE + 0x0008);
    *VDP_DATA = *RAM_SPRITE_2_POS_Y;

    // Sprite 2's X coordinate is at table+0x000E
    SetVRAMWrite(VRAM_ADDR_SPRITE_TABLE + 0x000e);
    *VDP_DATA = *RAM_SPRITE_2_POS_X;
}