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Fixed premature wrapping of the envelope, played about with whether that should be subject to a predivision by 256. It feels unlikely?

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This commit is contained in:
Thomas Harte 2016-10-19 22:12:51 -04:00
parent 6073906c39
commit 319d7c2b12
1 changed files with 9 additions and 8 deletions
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17
Components/AY38910/AY38910.cpp
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@ -14,7 +14,8 @@ AY38910::AY38910() :
_selected_register(0),
_channel_output{0, 0, 0}, _channel_dividers{0, 0, 0}, _tone_generator_controls{0, 0, 0},
_noise_shift_register(0xffff), _noise_divider(0), _noise_output(0),
_envelope_divider(0), _envelope_period(0)
_envelope_divider(0), _envelope_period(0), _envelope_position(0),
_output_registers{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
{
_output_registers[8] = _output_registers[9] = _output_registers[10] = 0;
@ -87,13 +88,13 @@ void AY38910::get_samples(unsigned int number_of_samples, int16_t *target)
// (1) decrement, then shift a high-order bit right and mask to get 1 for did underflow, 0 otherwise;
// (2) did_underflow * a + (did_underflow ^ 1) * b to pick between reloading and not reloading
int did_underflow;
#define shift(x, r) \
x -= resulting_steps; \
#define shift(x, r, steps) \
x -= steps; \
did_underflow = (x >> 16)&1; \
x = did_underflow * r + (did_underflow^1) * x;
#define step_channel(c) \
shift(_channel_dividers[c], _tone_generator_controls[c]); \
shift(_channel_dividers[c], _tone_generator_controls[c], resulting_steps); \
_channel_output[c] ^= did_underflow;
// update the tone channels
@ -103,18 +104,19 @@ void AY38910::get_samples(unsigned int number_of_samples, int16_t *target)
// ... the noise generator. This recomputes the new bit repeatedly but harmlessly, only shifting
// it into the official 17 upon divider underflow.
shift(_noise_divider, _output_registers[6]&0x1f);
shift(_noise_divider, _output_registers[6]&0x1f, resulting_steps);
_noise_output ^= did_underflow&_noise_shift_register&1;
_noise_shift_register |= ((_noise_shift_register ^ (_noise_shift_register >> 3))&1) << 17;
_noise_shift_register >>= did_underflow;
// ... and the envelope generator. Table based for pattern lookup, with a 'refill' step — a way of
// implementing non-repeating patterns by locking them to table position 0x1f.
shift(_envelope_divider, _envelope_period);
// int envelope_divider = ((_master_divider ^ former_master_divider) >> 8) & 1;
shift(_envelope_divider, _envelope_period, resulting_steps);
_envelope_position += did_underflow;
int refill = _envelope_overflow_masks[_output_registers[13]] * (_envelope_position >> 5);
_envelope_position = (_envelope_position & 0x1f) | refill;
int envelope_volume = _envelope_shapes[_output_registers[13]][_envelope_position & 0xf];
int envelope_volume = _envelope_shapes[_output_registers[13]][_envelope_position];
#undef step_channel
#undef shift
@ -197,7 +199,6 @@ void AY38910::set_register_value(uint8_t value)
case 13:
masked_value &= 0xf;
_envelope_position = 0;
// printf("envelope %d\n", masked_value);
break;
}
_output_registers[selected_register] = masked_value;