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!

See github.com/visrealm/pico9918

Demos:

Graphics Mode I Demo

Graphics Mode II Demo

Text 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