From 09985655a21450d1798eef5d5b52a4aa6be0913d Mon Sep 17 00:00:00 2001
From: Toby Jaffey <toby@ringtailsoftware.co.uk>
Date: Mon, 15 Dec 2025 10:48:10 +0000
Subject: [PATCH] Fix host-sdl/doom audio. Have app ask via syscall if audio
 can be rendered before sending, else any mismatch in rates will cause queue
 over/underflow in host-sdl.

---
 apps/zigdoom/src/main.zig    |  6 ++++--
 apps/zigdoom/src/uvm.zig     |  4 ++++
 common/uvm32_common_custom.h |  1 +
 hosts/host-sdl/host-sdl.c    | 13 +++++++------
 4 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/apps/zigdoom/src/main.zig b/apps/zigdoom/src/main.zig
index 5d59e3f..3cabdda 100644
--- a/apps/zigdoom/src/main.zig
+++ b/apps/zigdoom/src/main.zig
@@ -198,8 +198,10 @@ fn submain() !void {
 
     while(true) {
         pd.doom_update();
-        const doomSndBuf: [*]i16 = pd.doom_get_sound_buffer();
-        uvm.renderAudio(doomSndBuf, 2048);
+        if (uvm.canRenderAudio()) {
+            const doomSndBuf: [*]i16 = pd.doom_get_sound_buffer();
+            uvm.renderAudio(doomSndBuf, 2048);
+        }
 
         const fb: [*]const u8 = pd.doom_get_framebuffer(4);
         uvm.render(fb, WIDTH * HEIGHT * 4);
diff --git a/apps/zigdoom/src/uvm.zig b/apps/zigdoom/src/uvm.zig
index 250f8f7..5eedcda 100644
--- a/apps/zigdoom/src/uvm.zig
+++ b/apps/zigdoom/src/uvm.zig
@@ -24,6 +24,10 @@ pub inline fn syscall(id: u32, param1: u32, param2: u32) u32 {
     return val;
 }
 
+pub inline fn canRenderAudio() bool {
+    return syscall(uvm32.UVM32_SYSCALL_CANRENDERAUDIO, 0, 0) != 0;
+}
+
 pub inline fn renderAudio(audbuf: [*]const i16, len:u32) void {
     _ = syscall(uvm32.UVM32_SYSCALL_RENDERAUDIO, @intFromPtr(audbuf), len);
 }
diff --git a/common/uvm32_common_custom.h b/common/uvm32_common_custom.h
index 0d74097..6d06b52 100644
--- a/common/uvm32_common_custom.h
+++ b/common/uvm32_common_custom.h
@@ -13,4 +13,5 @@
 #define UVM32_SYSCALL_RENDER      0x00000008
 #define UVM32_SYSCALL_GETKEY      0x00000009
 #define UVM32_SYSCALL_RENDERAUDIO 0x0000000A
+#define UVM32_SYSCALL_CANRENDERAUDIO 0x0000000B
 
diff --git a/hosts/host-sdl/host-sdl.c b/hosts/host-sdl/host-sdl.c
index f640521..a305863 100644
--- a/hosts/host-sdl/host-sdl.c
+++ b/hosts/host-sdl/host-sdl.c
@@ -34,7 +34,7 @@ static int keyBufferWr = 0;
 static int keyBufferRd = 0;
 
 // circular buffer of audio samples, so vm code can read them as it's ready
-#define AUDIOBUFFER_LEN 4096
+#define AUDIOBUFFER_LEN (2048*10)
 static int16_t audioBuffer[AUDIOBUFFER_LEN];
 static int audioBufferWr = 0;
 static int audioBufferRd = 0;
@@ -134,7 +134,7 @@ void audiocb(void *userdata, SDL_AudioStream *stream, int additional_amount, int
         return;
     }
     
-    while(total_amount > 0) {
+    while(additional_amount > 0) {
         int16_t sample[2];
 
         // always expect audio in pairs
@@ -147,7 +147,7 @@ void audiocb(void *userdata, SDL_AudioStream *stream, int additional_amount, int
         } else {
             return;
         }
-        total_amount -= 4;
+        additional_amount -= 4;
     }
 }
 
@@ -251,7 +251,7 @@ int main(int argc, char *argv[]) {
     SDL_AudioSpec srcspec = {
         .format = SDL_AUDIO_S16,
         .channels = 2,
-        .freq = 44100,
+        .freq = 11025,
     };
 
     SDL_AudioStream *stream = SDL_OpenAudioDeviceStream(SDL_AUDIO_DEVICE_DEFAULT_PLAYBACK, &srcspec, audiocb, NULL);
@@ -339,14 +339,15 @@ int main(int argc, char *argv[]) {
                     case UVM32_SYSCALL_GETC: {
                         uvm32_arg_setval(vmst, &evt, RET, 0xFFFFFFFF);
                     } break;
+                    case UVM32_SYSCALL_CANRENDERAUDIO:
+                        uvm32_arg_setval(vmst, &evt, RET, audioBufferWr == audioBufferRd);  // queue is empty
+                    break;
                     case UVM32_SYSCALL_RENDERAUDIO: {
                         uvm32_slice_t buf = uvm32_arg_getslice(vmst, &evt, ARG0, ARG1);
-                        printf("Got audio buf len=%d\n", buf.len);
                         int16_t *samples = (int16_t *)buf.ptr;
                         for (int i=0;i<buf.len/2;i++) {
                             audio_enq(samples[i]);
                         }
-
                     } break;
                     case UVM32_SYSCALL_RENDER: {
                         uvm32_slice_t buf = uvm32_arg_getslice(vmst, &evt, ARG0, ARG1);