Kwak-8

This section gives you an overview of the capabilities. For specific port numbers of the described capabilities, refer to https://github.com/Lerc/kwak-8/blob/master/IOMapping.txt

Display

The Kwak-8 has two display resolutions. Standard resolution is 240x180, hires mode is twice that at 480x360. Display frames are assembled in a write only-display buffer that is 512x392.

Writing 0x80 to port 0x40 places a portion of the buffer onscreemn in lowres mode;

Writing 0x81 to port 0x40 places a portion of the buffer onscreemn in hirres mode;

• Display modes

  These set all of the pixels on the output buffer reading from RAM and hardware registers. The translation method of data to pixels is dependent on the mode

• Blitter.

  You can write rectangles of data to screen in pixel formats of 2,3,4,8 pixels per byte. Blits can be X-flipped, Y-Flipped, X-Doubled, Y-Doubled, and support color 0 transparency.

• Serial Pixels

  You can position a pointer at a display position and serially write bytes to the display. This gives you access to 256 colour output. There are also some blending options available to multiply or add to the existing pixels. This is the most versatile display output mechanism but requires that the CPU do all of the display generation on its own.

An alternative method would be to simply host a framebuffer in RAM and do a single 240x180 Blit to place it onscreen. At 2 bytes per pixel a blit of 120 bytes wide and 180 high would fill the display but would also require a third of the RAM to hold the image.

Choosing the right combination of display methods requires weighing up the pros and cons. Displays that take up less RAM mean there will be less data that needs to be manipulated, possibly making them faster, but they are also less flexible, which in turn might make them slower. Clever use within the constraints is where much of the lasting appeal of 8-bit development lies.

Audio

There are 8 synth voices available on the Kwak-8.

Each voice has
• One of 256 basic waveforms
• A frequency range of 0...3900Hz
• Independant volume (256 levels)
• Pitch bend/occilation
• Random noise (16 levels)
• An attack-hold-release envelope

This asm example shows how simple it is to play a sound from 8 bytes of data stored in memory

  ldi r16,3         //play on voice 3
  out voice_Select,r16
  ldi XL, low(SoundData)  // SoundData holds the 8 bytes of the sound effect.
  ldi XH, high(SoundData)
  ld  r0,X+
  out voice_Freq_L,r0
  ld  r0,X+
  out voice_Freq_H,r0
  ld  r0,X+
  out voice_Volume,r0
  ld  r0,X+
  out voice_WaveShape,r0
  ld  r0,X+
  out voice_BendWave,r0
  ld  r0,X+
  out voice_BendAmplitude,r0
  ld  r0,X+
  out voice_NoiseHold,r0
  ld  r0,X+
  out voice_AttackRelease,r0  //writing to this port triggers the Attack-hold-release cycle
      

Input

The eight ports for input reside at the same port addresses as the display. The display registers are write-only registers. The input registers are read-only registers at the same location.

• Up/Down/Left/Right cursor keys
• WASD direction keys
• Enter
• SpaceBar
• BackSpace
• Esc
• Ctrl
• Shift
• Z
• X

X and Y mouse coordinates are provided in a range of 0...255 measured in low-res pixels. Mouse buttons map to the same bits as Z, X, and BackSpace

There are two 8-bit time inputs.

• A frame counter that increments with each video frame
• A Second ticker that increments once per second

Finally, there is a console input. This port reads from a buffer that can hold 10 ascii characters, the port returns zero when the buffer is empty