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vrEmuTms9918 - TMS9918 / TMS9918A / TMS9929A VDP Emulator

TMS9918 emulator. Core engine written in C99. Zero dependencies.

The goal is to emulate all documented modes listed in the TMS9918A/TMS9928A/TMS9929A datasheet

Supported Modes

  • Graphics I (including sprites)
  • Graphics II (including sprites)
  • Multicolor mode (including sprites)
  • Text

Other features

  • 5th sprite
  • Sprite collisions
  • VSYNC interrupt
  • Individual scanline rendering

PICO9918

This library is also being used in the PICO9918 project. A drop-in replacement for a physical TMS9918A powered by a Raspberry Pi Pico.

The PICO9918 running in an original TI-99/4A:

Don't mess with Texas!

PICO9918 Prototype - Don't mess with Texas

See github.com/visrealm/pico9918

Demos:

Graphics Mode I Demo

Graphics Mode I Demo

Graphics Mode II Demo

Graphics Mode II Demo

Text Mode Demo

Text Mode Demo

Multicolor Mode Demo

Multicolor Mode Demo

Building

vrEmuTms9918 uses the CMake build system

Checkout repository

git clone https://github.com/visrealm/vrEmuTms9918.git
cd vrEmuTms9918

Setup build

mkdir build
cd build
cmake ..

Build

cmake --build .

Windows: Optionally, open the generated solution file

Run tests

ctest

Windows: Optionally, build the ALL_TESTS project in the generated solution file

Quick start

#include "vrEmuTms9918.h"
#include "vrEmuTms9918Util.h"

#define TMS_VRAM_NAME_ADDRESS          0x3800
#define TMS_VRAM_COLOR_ADDRESS         0x0000
#define TMS_VRAM_PATT_ADDRESS          0x2000
#define TMS_VRAM_SPRITE_ATTR_ADDRESS   0x3B00
#define TMS_VRAM_SPRITE_PATT_ADDRESS   0x1800

// program entry point
int main()
{
  // create a new tms9918
  VrEmuTms9918 *tms9918 = vrEmuTms9918New();
  
  // Here, we're using the helper functions provided by vrEmuTms9918Util.h
  //
  // In a full system emulator, the only functions required (connected to the system bus) would be:
  //
  //  * vrEmuTms9918WriteAddr()
  //  * vrEmuTms9918WriteData()
  //  * vrEmuTms9918ReadStatus()
  //  * vrEmuTms9918ReadData()
  //
  // The helper functions below wrap the above functions and are not required.
  // vrEmuTms9918Util.h/c can be omitted if you're not using them.
  //
  // For a full example, see https://github.com/visrealm/hbc-56/blob/master/emulator/src/devices/tms9918_device.c
  
  // set up the VDP write-only registers
  vrEmuTms9918WriteRegisterValue(tms9918, TMS_REG_0, TMS_R0_MODE_GRAPHICS_I);
  vrEmuTms9918WriteRegisterValue(tms9918, TMS_REG_1, TMS_R1_MODE_GRAPHICS_I | TMS_R1_RAM_16K);
  vrEmuTms9918SetNameTableAddr(tms9918, TMS_VRAM_NAME_ADDRESS);
  vrEmuTms9918SetColorTableAddr(tms9918, TMS_VRAM_COLOR_ADDRESS);
  vrEmuTms9918SetPatternTableAddr(tms9918, TMS_VRAM_PATT_ADDRESS);
  vrEmuTms9918SetSpriteAttrTableAddr(tms9918, TMS_VRAM_SPRITE_ATTR_ADDRESS);
  vrEmuTms9918SetSpritePattTableAddr(tms9918, TMS_VRAM_SPRITE_PATT_ADDRESS);
  vrEmuTms9918SetFgBgColor(tms9918, TMS_BLACK, TMS_CYAN);
  
  // send it some data (a pattern)
  vrEmuTms9918SetAddressWrite(tms9918, TMS_VRAM_PATT_ADDRESS);

  // update pattern #0
  char smile[] = {0b00111100,
                  0b01000010,
                  0b10000001,
                  0b10100101,
                  0b10000001,
                  0b10011001,
                  0b01000010,
                  0b00111100};
  vrEmuTms9918WriteBytes(tms9918, smile, sizeof(smile));
  
  // update fg/bg color for first 8 characters
  vrEmuTms9918SetAddressWrite(tms9918, TMS_VRAM_COLOR_ADDRESS)
  vrEmuTms9918WriteData(tms9918, vrEmuTms9918FgBgColor(TMS_BLACK, TMS_LT_YELLOW));
 
  // output smile pattern to screen
  vrEmuTms9918SetAddressWrite(tms9918, TMS_VRAM_NAME_ADDRESS);

  // a few smiles
  vrEmuTms9918WriteData(tms9918, 0x00);
  vrEmuTms9918WriteData(tms9918, 0x00);
  vrEmuTms9918WriteData(tms9918, 0x00);
  
  // render the display
  char scanline[TMS9918A_PIXELS_X]; // scanline buffer

  // an example output (a framebuffer for an SDL texture)
  uint32_t frameBuffer[TMS9918A_PIXELS_X * TMS9918A_PIXELS_Y];

  // generate all scanlines and render to framebuffer
  uint32_t *pixPtr = frameBuffer;
  for (int y = 0; y < TMS9918A_PIXELS_Y; ++y)
  {
    // get the scanline pixels
    vrEmuTms9918ScanLine(tms9918, y, scanline);
    
    for (int x = 0; x < TMS9918A_PIXELS_X; ++x)
    {
      // values returned from vrEmuTms9918ScanLine() are palette indexes
      // use the vrEmuTms9918Palette array to convert to an RGBA value      
      *pixPtr++ = vrEmuTms9918Palette[scanline[x]];
    }    
  }
  
  // output the buffer...
  
  ...
  
  
  // clean up
  
  vrEmuTms9918Destroy(tms9918);
  tms9918 = NULL;
  
  return 0;
}

Real example

This library is used in the HBC-56 emulator.

The HBC-56 uses this library to support:

  • Rendering to an SDL texture.
  • TMS9918 VSYNC Interrupts.
  • Time-based rendering. Supports beam-time.

Full source: hbc-56/emulator/src/devices/tms9918_device.c

License

This code is licensed under the MIT license