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Simplified sound generation.

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This commit is contained in:
Thomas Harte 2016-04-04 22:22:19 -04:00
parent c0cd1ed89e
commit 7838507a7a
2 changed files with 19 additions and 17 deletions
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35
Machines/Electron/Electron.cpp
View File

@ -66,7 +66,11 @@ void Machine::setup_output()
"}");
_crt->set_output_device(Outputs::CRT::Monitor);
_speaker.set_input_rate(125000);
// The maximum output frequency is 62500Hz and all other permitted output frequencies are integral divisions of that;
// nevertheless sampling only at 62500Hz may introduce aliasing errors as setting the speaker on or off can happen on
// any 2Mhz cycle, and I've no idea whether it has an immediate effect or happens only on the next clock. If it turns
// out that the former is the case, I'll need to turn this up to 2000000.
_speaker.set_input_rate(62500);
}
unsigned int Machine::perform_bus_operation(CPU6502::BusOperation operation, uint16_t address, uint8_t *value)
@ -468,8 +472,8 @@ inline void Machine::update_audio()
{
int difference = (int)_frameCycles - _audioOutputPosition;
_audioOutputPosition = (int)_frameCycles;
_speaker.run_for_cycles((_audioOutputPositionError + difference) >> 4);
_audioOutputPositionError = (_audioOutputPositionError + difference)&15;
_speaker.run_for_cycles((_audioOutputPositionError + difference) >> 5);
_audioOutputPositionError = (_audioOutputPositionError + difference)&31;
}
inline void Machine::start_pixel_line()
@ -782,25 +786,24 @@ void Machine::set_key_state(Key key, bool isPressed)
void Speaker::get_samples(unsigned int number_of_samples, int16_t *target)
{
while(number_of_samples--)
if(_is_enabled)
{
*target = _is_enabled ? _output_level : 0;
target++;
skip_samples(1);
while(number_of_samples--)
{
*target = (int16_t)((_counter / (_divider+1)) * 8192);
target++;
_counter = (_counter + 1) % ((_divider+1) * 2);
}
}
else
{
memset(target, 0, sizeof(int16_t) * number_of_samples);
}
}
void Speaker::skip_samples(unsigned int number_of_samples)
{
while(number_of_samples--)
{
_counter ++;
if(_counter > _divider*2)
{
_counter = 0;
_output_level ^= 8192;
}
}
_counter = (_counter + number_of_samples) % ((_divider+1) * 2);
}
void Speaker::set_divider(uint8_t divider)

1
Machines/Electron/Electron.hpp
View File

@ -130,7 +130,6 @@ class Speaker: public ::Outputs::Filter<Speaker> {
unsigned int _counter;
uint8_t _divider;
bool _is_enabled;
int16_t _output_level;
};
/*!