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Fix envelope generator freezing when envelope period is 0 #13

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Fix envelope generator freezing when envelope period is 0 #13

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18 changes: 15 additions & 3 deletions html/src/main/java/emu/joric/gwt/GwtAYPSG.java
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Original file line number Diff line number Diff line change
Expand Up @@ -151,12 +151,18 @@ public void init(Via via, Keyboard keyboard, Snapshot snapshot) {
updateStep = (int) (((long) step * 8L * (long) SAMPLE_RATE) / (long) CLOCK_1MHZ);
output = new int[] { 0, 0, 0, 0xFF };
count = new int[] { updateStep, updateStep, updateStep, 0x7fff, updateStep };
period = new int[] { updateStep, updateStep, updateStep, updateStep, 0 };
// Every period must be non-zero: writeSample's counter catch-up loops
// never terminate on a zero period.
period = new int[] { updateStep, updateStep, updateStep, updateStep, updateStep };
registers = new int[16];

volumeA = volumeB = volumeC = volumeEnvelope = 0;
disableToneA = disableToneB = disableToneC = disableAllNoise = false;
countEnv = hold = alternate = attack = holding = 0;
countEnv = hold = alternate = attack = 0;
// The envelope starts out holding, as if the reset-default shape 0
// (decay then hold) had already completed its decay to 0. It starts
// moving when a program first writes the envelope shape register.
holding = 1;
enable = 0;
outNoise = 0;
random = 1;
Expand Down Expand Up @@ -384,6 +390,12 @@ public void writeRegister(int address, int value) {
case 0x0B:
case 0x0C: {
int val = (((registers[0x0C] << 8) | registers[0x0B]) * updateStep) << 1;
// On the real chip an envelope period register value of 0 runs at
// twice the speed of period 1, i.e. a full 16-step envelope cycle
// in 128us at 1 MHz. (This is unlike the tone and noise periods,
// where 0 behaves the same as 1.) Period 1 is (updateStep << 1)
// here, so period 0 maps to half of that, which is updateStep.
val = (val == 0 ? updateStep : val);
int last = period[ENVELOPE];
period[ENVELOPE] = val;
int newCount = count[ENVELOPE] - (val - last);
Expand Down Expand Up @@ -514,7 +526,7 @@ public void writeSample() {
left -= add;
} while (left > 0);

if (holding == 0 && period[ENVELOPE] != 0) {
if (holding == 0) {
if ((count[ENVELOPE] -= step) <= 0) {
int ce = countEnv;
int envelopePeriod = period[ENVELOPE];
Expand Down
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