diff --git a/bend2/effs/audio.c b/bend2/effs/audio.c
index 7e9b9e217..abba58116 100644
--- a/bend2/effs/audio.c
+++ b/bend2/effs/audio.c
@@ -108,15 +108,23 @@ static void io_ring_free(IoRing* p) {
 
 // A thread feeds the default ALSA device 256 frames at a time (a
 // write blocks until the device has room, so the ring drains at the
-// device's clock).
+// device's clock). A chunk stays until the device has taken all of it;
+// an error ALSA can't recover stops the thread, and the ring fills as
+// with a stalled device.
 static void* io_ring_pump(void* ctx) {
-  IoRing* p = ctx;
+  IoRing* p  = ctx;
   float   out[256 * 2];
+  u32     at = 256;
   while (atomic_load_explicit(&p->done, memory_order_relaxed) == 0) {
-    io_ring_pull(p, out, 256);
-    snd_pcm_sframes_t n = snd_pcm_writei(p->unit, out, 256);
-    if (n < 0) {
-      snd_pcm_recover(p->unit, (int)n, 1);
+    if (at == 256) {
+      io_ring_pull(p, out, 256);
+      at = 0;
+    }
+    snd_pcm_sframes_t n = snd_pcm_writei(p->unit, out + at * 2, 256 - at);
+    if (n > 0) {
+      at += (u32)n;
+    } else if (n == 0 || snd_pcm_recover(p->unit, (int)n, 1) < 0) {
+      break;
     }
   }
   return NULL;
diff --git a/tests/io/audio_linux_progress.bend b/tests/io/audio_linux_progress.bend
new file mode 100644
index 000000000..6663d557b
--- /dev/null
+++ b/tests/io/audio_linux_progress.bend
@@ -0,0 +1,52 @@
+# The Linux audio pump against injected ALSA write results (ALSA's null
+# output underneath, so no device). Other systems run no cases.
+import Base
+
+def AudioTest.count() -> IO(U32):
+  import "./audio_linux_progress.c"
+  import "./audio_linux_progress.js"
+
+def AudioTest.start(i: U32) -> IO(Unit):
+  import "./audio_linux_progress.c"
+  import "./audio_linux_progress.js"
+
+def AudioTest.wait() -> IO(Unit):
+  import "./audio_linux_progress.c"
+  import "./audio_linux_progress.js"
+
+def AudioTest.closed() -> IO(Unit):
+  import "./audio_linux_progress.c"
+  import "./audio_linux_progress.js"
+
+def samples(n: Nat, +i: U32) -> List<&2, F32>:
+  match n:
+    case 0n:
+      []
+    case 1n+p:
+      +x = U32.to_f32(i)
+      x <> ((0.0 - x : F32) <> samples(p, (i + 1 : U32)))
+
+def close_pair(pair: Audio & U32) -> IO(Unit):
+  (a, queued) = pair
+  Audio.close(a)
+
+def cases(n: Nat, +i: U32) -> IO(Unit):
+  match n:
+    case 0n:
+      IO.print("audio")
+    case 1n+p:
+      do IO<Unit>:
+        Unit <- AudioTest.start(i)
+        a : Audio <- IO.try(Audio, Audio.open(48000))
+        pair : Audio & U32 <- Audio.write(a, samples(512n, 1))
+        Unit <- AudioTest.wait()
+        Unit <- close_pair(pair)
+        Unit <- AudioTest.closed()
+        cases(p, (i + 1 : U32))
+
+def main() -> IO(Unit):
+  do IO<Unit>:
+    n : U32 <- AudioTest.count()
+    cases(U32.to_nat(n), 0)
+
+#|audio
diff --git a/tests/io/audio_linux_progress.c b/tests/io/audio_linux_progress.c
new file mode 100644
index 000000000..fde8789f2
--- /dev/null
+++ b/tests/io/audio_linux_progress.c
@@ -0,0 +1,137 @@
+#ifdef __linux__
+#include <alsa/asoundlib.h>
+#include <dlfcn.h>
+
+// Writes of real samples (frame k is k, -k) get the case's result; the
+// rest reach ALSA's null output. Cases 0-254: the first write takes
+// 1-255 frames. Then: EINTR once, EPIPE once, every write capped at 17,
+// 64 frames then EINTR, 64 then EPIPE (all deliver 512 frames in
+// order), ENODEV always and 0 always (the pump stops after one write).
+enum { SHORT = 255, EINTR1, EPIPE1, CAP17, PART_EINTR, PART_EPIPE, DEAD, ZERO, CASES };
+
+static snd_pcm_t* audio_test_unit;
+static void*      audio_test_lib;
+static pthread_key_t audio_test_key;
+static u32 audio_test_case;
+static _Atomic(u32) audio_test_frames, audio_test_bad, audio_test_writes;
+static _Atomic(u32) audio_test_recovers, audio_test_stopped;
+
+static void audio_test_exit(void* p) {
+  atomic_store(&audio_test_stopped, 1);
+}
+
+static void* audio_test_sym(const char* name) {
+  void* p = snd_dlsym(audio_test_lib, name, NULL);
+  if (p == NULL) err_fail("audio test: missing ALSA symbol");
+  return p;
+}
+
+int snd_pcm_open(snd_pcm_t** p, const char* name, snd_pcm_stream_t s, int mode) {
+  int (*open)(snd_pcm_t**, const char*, snd_pcm_stream_t, int) = audio_test_sym("snd_pcm_open");
+  int code = open(p, "null", s, mode);
+  if (code == 0) audio_test_unit = *p;
+  return code;
+}
+
+typedef snd_pcm_sframes_t (*Write)(snd_pcm_t*, const void*, snd_pcm_uframes_t);
+
+snd_pcm_sframes_t snd_pcm_writei(snd_pcm_t* p, const void* data, snd_pcm_uframes_t frames) {
+  Write write = audio_test_sym("snd_pcm_writei");
+  const float* pcm = data;
+  pthread_setspecific(audio_test_key, (void*)1);
+  bool real = false;
+  for (u64 i = 0; i < frames; ++i) real |= pcm[i * 2] != 0;
+  if (p == audio_test_unit && real) {
+    u32 c    = audio_test_case;
+    u32 call = atomic_fetch_add(&audio_test_writes, 1);
+    if (call > 100000) err_fail("audio test: unbounded writes");
+    if (c < SHORT && call == 0) frames = c + 1;
+    if (c == CAP17 && frames > 17) frames = 17;
+    if ((c == PART_EINTR || c == PART_EPIPE) && call == 0) frames = 64;
+    if ((c == EINTR1 && call == 0) || (c == PART_EINTR && call == 1)) return -EINTR;
+    if ((c == EPIPE1 && call == 0) || (c == PART_EPIPE && call == 1)) return -EPIPE;
+    if (c == DEAD) return -ENODEV;
+    if (c == ZERO) return 0;
+  }
+  snd_pcm_sframes_t n = write(p, data, frames);
+  if (n > 0 && p == audio_test_unit) {
+    u32 k = atomic_load(&audio_test_frames);
+    for (snd_pcm_sframes_t i = 0; i < n; ++i) {
+      if (pcm[i * 2] == 0) continue;
+      ++k;
+      if (pcm[i * 2] != (float)k || pcm[i * 2 + 1] != -(float)k) atomic_store(&audio_test_bad, 1);
+    }
+    atomic_store(&audio_test_frames, k);
+  }
+  return n;
+}
+
+int snd_pcm_recover(snd_pcm_t* p, int code, int silent) {
+  int (*recover)(snd_pcm_t*, int, int) = audio_test_sym("snd_pcm_recover");
+  if (p == audio_test_unit) atomic_fetch_add(&audio_test_recovers, 1);
+  return recover(p, code, silent);
+}
+#endif
+
+Term audio_test_count_run(Env e, Term* f, IoWork* w) {
+#ifdef __linux__
+  return CASES;
+#endif
+  return 0;
+}
+
+Term audio_test_start_run(Env e, Term* f, IoWork* w) {
+#ifdef __linux__
+  audio_test_case = (u32)f[0];
+  atomic_store(&audio_test_frames, 0);
+  atomic_store(&audio_test_bad, 0);
+  atomic_store(&audio_test_writes, 0);
+  atomic_store(&audio_test_recovers, 0);
+  atomic_store(&audio_test_stopped, 0);
+#endif
+  return term_pak(CID(Unit), 0);
+}
+
+// Waits for all 512 frames, or for the pump to stop on a dead device.
+Term audio_test_wait_run(Env e, Term* f, IoWork* w) {
+#ifdef __linux__
+  u32  c    = audio_test_case;
+  bool dead = c == DEAD || c == ZERO;
+  u64  t0   = io_tick();
+  while (dead ? !atomic_load(&audio_test_stopped) : atomic_load(&audio_test_frames) < 512) {
+    if (atomic_load(&audio_test_bad) || io_tick() - t0 > 1000000000ull) {
+      fprintf(stderr, "audio test case %u: frames=%u writes=%u recovers=%u\n", c,
+        atomic_load(&audio_test_frames), atomic_load(&audio_test_writes),
+        atomic_load(&audio_test_recovers));
+      err_fail("audio test: pump lost or reordered frames");
+    }
+    struct timespec t = { 0, 100000 };
+    nanosleep(&t, NULL);
+  }
+  if (dead && (atomic_load(&audio_test_writes) != 1
+    || atomic_load(&audio_test_recovers) != (c == DEAD)))
+    err_fail("audio test: dead device retried");
+#endif
+  return term_pak(CID(Unit), 0);
+}
+
+Term audio_test_closed_run(Env e, Term* f, IoWork* w) {
+#ifdef __linux__
+  if (!atomic_load(&audio_test_stopped)) err_fail("audio test: close did not join the pump");
+  if (audio_test_case != DEAD && audio_test_case != ZERO && atomic_load(&audio_test_frames) != 512)
+    err_fail("audio test: final frames");
+#endif
+  return term_pak(CID(Unit), 0);
+}
+
+static void __attribute__((constructor)) audio_test_use(void) {
+#ifdef __linux__
+  audio_test_lib = snd_dlopen(NULL, RTLD_LAZY, NULL, 0);
+  if (audio_test_lib == NULL || pthread_key_create(&audio_test_key, audio_test_exit))
+    err_fail("audio test: setup");
+#endif
+  io_eff(CID(AudioTest.count), audio_test_count_run);
+  io_eff(CID(AudioTest.start), audio_test_start_run);
+  io_eff(CID(AudioTest.wait), audio_test_wait_run);
+  io_eff(CID(AudioTest.closed), audio_test_closed_run);
+}
diff --git a/tests/io/audio_linux_progress.js b/tests/io/audio_linux_progress.js
new file mode 100644
index 000000000..9ca3bd0f2
--- /dev/null
+++ b/tests/io/audio_linux_progress.js
@@ -0,0 +1,5 @@
+// The cases run only in the Linux C lane.
+io_eff(CID(AudioTest.count), () => 0);
+io_eff(CID(AudioTest.start), () => ({ $: CID(Unit) }));
+io_eff(CID(AudioTest.wait), () => ({ $: CID(Unit) }));
+io_eff(CID(AudioTest.closed), () => ({ $: CID(Unit) }));