Chiptable

Chiptable is, at present, just an ethereal proof of concept for a multi-channel WaveBoy-like soundcard for the Commander X16 or similar 6502 computer.

The idea is a multi-channel audio solution combining the variable clocked DAC of the WaveBoy and applying to a sort of hybrid between LSDJ wave frames and the TG16 sound solution.

The idea is to support 8 voices (channels) with each channel having 256 bytes of sample data divided into 8 frames. Two modes will be supported:

A frame/window mode, which mirrors that of the WaveBoy in that it repeatedly cycles through the 32 samples providing a cyclic waveform. This can be either at fixed 8 block sections or in a free frame mode, where the frame window can move across all 256 bytes (looking at a 32 byte slice).

Or a jumbo frame mode, which operates across the full 256 byte sample and can be used for very short audio clips or long cycles.

Why 256 bytes and 8 frames instead of 512 and 16? This is to be determined but on 8-bit platforms, like those using a 6502 CPU, this presents a nice boundary for efficient loops.

To provide more flexibility, similar to the WaveBoy, there will be a loadable bank of frames/samples which can be loaded directly onto the sound card. How many samples depends on the capability of the microcontroller/FPGA but if looking at the RP2040, up to 256 samples (of 256 bytes) are possible, perhaps more.

Memory Usage

RAM Usage

Sample Banks: (256 * 256) 64k

ROM LUTs

Note/Semi to Timer Value: (64k * 3 bytes) 192k LFO Sine: ??

Proposed Microcontrollers

RP2040

Clock Freq: 133 MHz
SRAM: 264k
Flash: 2MB
Timers:
1x 64-bit global
8x PWM 16-bit
8x PIO 32-bit
4x DMA
2x Cortex (microsecond)

RP2350

Clock Freq: 150 MHz
SRAM: 520k
Flash: 4MB
Timers:
2x 64-bit global
12x PWM 16-bit
12x PIO 32-bit
4x DMA
2x Cortex (microsecond)
1x RISCV SIO

Ideas

Consider a UART instead of MMIO? (See: https://discord.com/channels/547559626024157184/547560914744901644/1439781003370561657)