// ---------------------------------------------------------------------------- // Set chip model. // ---------------------------------------------------------------------------- public void set_chip_model(siddefs.chip_model model)//chip_model model) { wave.set_chip_model(model); envelope.set_chip_model(model); if (model == siddefs.chip_model.MOS6581) { // The waveform D/A converter introduces a DC offset in the signal // to the envelope multiplying D/A converter. The "zero" level of // the waveform D/A converter can be found as follows: // // Measure the "zero" voltage of voice 3 on the SID audio output // pin, routing only voice 3 to the mixer ($d417 = $0b, $d418 = // $0f, all other registers zeroed). // // Then set the sustain level for voice 3 to maximum and search for // the waveform output value yielding the same voltage as found // above. This is done by trying out different waveform output // values until the correct value is found, e.g. with the following // program: // // lda #$08 // sta $d412 // lda #$0b // sta $d417 // lda #$0f // sta $d418 // lda #$f0 // sta $d414 // lda #$21 // sta $d412 // lda #$01 // sta $d40e // // ldx #$00 // lda #$38 ; Tweak this to find the "zero" level //l cmp $d41b // bne l // stx $d40e ; Stop frequency counter - freeze waveform output // brk // // The waveform output range is 0x000 to 0xfff, so the "zero" // level should ideally have been 0x800. In the measured chip, the // waveform output "zero" level was found to be 0x380 (i.e. $d41b // = 0x38) at an audio output voltage of 5.94V. // // With knowledge of the mixer op-amp characteristics, further estimates // of waveform voltages can be obtained by sampling the EXT IN pin. // From EXT IN samples, the corresponding waveform output can be found by // using the model for the mixer. // // Such measurements have been done on a chip marked MOS 6581R4AR // 0687 14, and the following results have been obtained: // * The full range of one voice is approximately 1.5V. // * The "zero" level rides at approximately 5.0V. // wave_zero = 0x380; } else { // No DC offsets in the MOS8580. wave_zero = 0x800; } }
public void set_chip_model(siddefs.chip_model model) { sid_model = model; }