From 76a6b17e4759cf59a202024f07da247c10a5f7ec Mon Sep 17 00:00:00 2001
From: Zachary Hall <catmeow72@proton.me>
Date: Tue, 15 Oct 2024 15:13:18 -0700
Subject: [PATCH] Fix PCM data calculation

---
 backends/playback/zsm/x16emu/vera_pcm.c | 21 +++++++++++++----
 backends/playback/zsm/zsm_backend.hpp   | 31 +++++++++++++------------
 2 files changed, 32 insertions(+), 20 deletions(-)

diff --git a/backends/playback/zsm/x16emu/vera_pcm.c b/backends/playback/zsm/x16emu/vera_pcm.c
index 8dbe1e2..1e617c7 100644
--- a/backends/playback/zsm/x16emu/vera_pcm.c
+++ b/backends/playback/zsm/x16emu/vera_pcm.c
@@ -181,11 +181,22 @@ pcm_render(int16_t *buf, unsigned num_samples)
 	}
 }
 uint32_t pcm_fifo_avail(void) {
+	uint32_t cnt_adj = fifo_cnt;
 	switch ((ctrl >> 4) & 3) {
-		case 0: return fifo_cnt;
-		case 1: return fifo_cnt / 2;
-		case 2: return fifo_cnt / 2;
-		case 3: return fifo_cnt / 4;
+		case 3: cnt_adj /= 2;
+		case 2:
+		case 1: cnt_adj /= 2;
+		case 0: break;
 	}
-	return 0;
+	uint32_t output = 0;
+	uint32_t _phase = phase;
+	while (cnt_adj != 0) {
+		uint32_t _prev_phase = _phase;
+		_phase += rate;
+		if ((_phase & 0x80) != (_prev_phase & 0x80)) {
+			output++;
+			cnt_adj--;
+		}
+	}
+	return output;
 }
diff --git a/backends/playback/zsm/zsm_backend.hpp b/backends/playback/zsm/zsm_backend.hpp
index c6a37f8..1db5771 100644
--- a/backends/playback/zsm/zsm_backend.hpp
+++ b/backends/playback/zsm/zsm_backend.hpp
@@ -84,22 +84,23 @@ class ZsmBackend : public PlaybackBackend {
         return (int16_t)((((int32_t)a) + ((int32_t)b)) >> 1);
     }
     void audio_step(size_t samples) {
-        while (pcm_fifo_avail() < samples && remain > 0) {
-            remain--;
-            size_t oldpos = file->get_pos();
-            file->seek((cur++), SeekType::SET);
-            uint8_t sample;
-            file->read(&sample, 1, 1);
-            pcm_write_fifo(sample);
-            if (remain == 0) {
-                if (islooped) {
-                    cur = loop;
-                    remain = loop_rem;
-                }
-            }
-            file->seek(oldpos, SeekType::SET);
-        }
     	if (samples == 0) return;
+     	while (pcm_fifo_avail() < samples && remain > 0) {
+      		if (pcm_read_rate() == 0) break;
+             remain--;
+             size_t oldpos = file->get_pos();
+             file->seek((cur++), SeekType::SET);
+             uint8_t sample;
+             file->read(&sample, 1, 1);
+             pcm_write_fifo(sample);
+             if (remain == 0) {
+                 if (islooped) {
+                     cur = loop;
+                     remain = loop_rem;
+                 }
+             }
+             file->seek(oldpos, SeekType::SET);
+         }
         samples *= 2;
     	int16_t *psg_ptr = psg_buf.get_item_sized<int16_t>(samples);
         int16_t *pcm_ptr = pcm_buf.get_item_sized<int16_t>(samples);