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Simplified/corrected AY tone/noise mixer logic, and made a new guess at the effect of reading registers that are smaller than 8 bits.

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Thomas Harte 2016-11-09 21:21:17 -05:00
parent 9c550c594a
commit 77ce200fbb
1 changed files with 15 additions and 6 deletions
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21
Components/AY38910/AY38910.cpp
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@ -149,11 +149,12 @@ void AY38910::evaluate_output_volume()
// The output level for a channel is:
// 1 if neither tone nor noise is enabled;
// 0 if either tone or noise is enabled and its value is low.
// (which is implemented here with reverse logic, assuming _channel_output and _noise_output are already inverted)
#define level(c, tb, nb) \
(((((_output_registers[7] >> tb)&1)^1) & _tone_outputs[c]) | ((((_output_registers[7] >> nb)&1)^1) & _noise_output)) ^ 1
// The tone/noise enable bits use inverse logic — 0 = on, 1 = off — permitting the OR logic below.
#define tone_level(c, tone_bit) (_tone_outputs[c] | (_output_registers[7] >> tone_bit))
#define noise_level(c, noise_bit) (_noise_output | (_output_registers[7] >> noise_bit))
int channel_levels[3] = {
#define level(c, tone_bit, noise_bit) tone_level(c, tone_bit) & noise_level(c, noise_bit) & 1
const int channel_levels[3] = {
level(0, 0, 3),
level(1, 1, 4),
level(2, 2, 5),
@ -164,7 +165,7 @@ void AY38910::evaluate_output_volume()
#define channel_volume(c) \
((_output_registers[c] >> 4)&1) * envelope_volume + (((_output_registers[c] >> 4)&1)^1) * (_output_registers[c]&0xf)
int volumes[3] = {
const int volumes[3] = {
channel_volume(8),
channel_volume(9),
channel_volume(10)
@ -235,7 +236,15 @@ void AY38910::set_register_value(uint8_t value)
uint8_t AY38910::get_register_value()
{
return _registers[_selected_register];
// This table ensures that bits that aren't defined within the AY are returned as 1s
// when read. I can't find documentation on this and don't have a machine to test, so
// this is provisionally a guess. TODO: investigate.
const uint8_t register_masks[16] = {
0x00, 0xf0, 0x00, 0xf0, 0x00, 0xf0, 0xe0, 0x00,
0xe0, 0xe0, 0xe0, 0x00, 0x00, 0xf0, 0x00, 0x00
};
return _registers[_selected_register] | register_masks[_selected_register];
}
uint8_t AY38910::get_port_output(bool port_b)