git: a48bbef5eb32 - main - sound: Adjust mmap example to use kqueue
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Date: Wed, 17 Jun 2026 10:52:51 UTC
The branch main has been updated by christos:
URL: https://cgit.FreeBSD.org/src/commit/?id=a48bbef5eb32508a8d7b3b986c9b1d28176d1694
commit a48bbef5eb32508a8d7b3b986c9b1d28176d1694
Author: Goran Mekić <meka@tilda.center>
AuthorDate: 2026-06-17 10:36:12 +0000
Commit: Christos Margiolis <christos@FreeBSD.org>
CommitDate: 2026-06-17 10:50:44 +0000
sound: Adjust mmap example to use kqueue
Reviewed by: christos
Differential Revision: https://reviews.freebsd.org/D57410
---
share/examples/sound/mmap.c | 178 +++++++++++++-------------------------------
1 file changed, 50 insertions(+), 128 deletions(-)
diff --git a/share/examples/sound/mmap.c b/share/examples/sound/mmap.c
index 7f165d417020..3710483361ac 100644
--- a/share/examples/sound/mmap.c
+++ b/share/examples/sound/mmap.c
@@ -26,114 +26,18 @@
*/
/*
- * This program demonstrates low-latency audio pass-through using mmap.
- * Opens input and output audio devices using memory-mapped I/O,
- * synchronizes them in a sync group for simultaneous start,
- * then continuously copies audio data from input to output.
+ * This program demonstrates low-latency audio pass-through using mmap
+ * and kqueue. It opens input and output audio devices using memory-
+ * mapped I/O, synchronizes them in a sync group for simultaneous start,
+ * then continuously copies audio data from input to output. Buffer
+ * positions are obtained from kqueue's ext[0] (replacing GETIPTR/
+ * GETOPTR ioctls) and error counters from ext[1] (replacing GETERROR).
*/
-#include <time.h>
+#include <sys/event.h>
#include "oss.h"
-/*
- * Get current time in nanoseconds using monotonic clock.
- * Monotonic clock is not affected by system time changes.
- */
-static int64_t
-gettime_ns(void)
-{
- struct timespec ts;
-
- if (clock_gettime(CLOCK_MONOTONIC, &ts) != 0)
- err(1, "clock_gettime failed");
- return ((int64_t)ts.tv_sec * 1000000000LL + ts.tv_nsec);
-}
-
-/*
- * Sleep until the specified absolute time (in nanoseconds).
- * Uses TIMER_ABSTIME for precise timing synchronization.
- */
-static void
-sleep_until_ns(int64_t target_ns)
-{
- struct timespec ts;
-
- ts.tv_sec = target_ns / 1000000000LL;
- ts.tv_nsec = target_ns % 1000000000LL;
- if (clock_nanosleep(CLOCK_MONOTONIC, TIMER_ABSTIME, &ts, NULL) != 0)
- err(1, "clock_nanosleep failed");
-}
-
-/*
- * Calculate the number of frames to process per iteration.
- * Higher sample rates require larger steps to maintain efficiency.
- */
-static unsigned
-frame_stepping(unsigned sample_rate)
-{
- return (16U * (1U + (sample_rate / 50000U)));
-}
-
-/*
- * Update the mmap pointer and calculate progress.
- * Returns the absolute progress in bytes.
- *
- * fd: file descriptor for the audio device
- * request: ioctl request (SNDCTL_DSP_GETIPTR or SNDCTL_DSP_GETOPTR)
- * map_pointer: current pointer position in the ring buffer
- * map_progress: absolute progress in bytes
- * buffer_bytes: total size of the ring buffer
- * frag_size: size of each fragment
- * frame_size: size of one audio frame in bytes
- */
-static int64_t
-update_map_progress(int fd, unsigned long request, int *map_pointer,
- int64_t *map_progress, int buffer_bytes, int frag_size, int frame_size)
-{
- count_info info = {};
- unsigned delta, max_bytes, cycles;
- int fragments;
-
- if (ioctl(fd, request, &info) < 0)
- err(1, "Failed to get mmap pointer");
- if (info.ptr < 0 || info.ptr >= buffer_bytes)
- errx(1, "Pointer out of bounds: %d", info.ptr);
- if ((info.ptr % frame_size) != 0)
- errx(1, "Pointer %d not aligned to frame size %d", info.ptr,
- frame_size);
- if (info.blocks < 0)
- errx(1, "Invalid block count %d", info.blocks);
-
- /*
- * Calculate delta: how many bytes have been processed since last check.
- * Handle ring buffer wraparound using modulo arithmetic.
- */
- delta = (info.ptr + buffer_bytes - *map_pointer) % buffer_bytes;
-
- /*
- * Adjust delta based on reported blocks available.
- * This accounts for cases where the pointer has wrapped multiple times.
- */
- max_bytes = (info.blocks + 1) * frag_size - 1;
- if (max_bytes >= delta) {
- cycles = max_bytes - delta;
- cycles -= cycles % buffer_bytes;
- delta += cycles;
- }
-
- /* Verify fragment count matches expected value */
- fragments = delta / frag_size;
- if (info.blocks < fragments || info.blocks > fragments + 1)
- warnx("Pointer block mismatch: ptr=%d blocks=%d delta=%u",
- info.ptr, info.blocks, delta);
-
- /* Update pointer and progress tracking */
- *map_pointer = info.ptr;
- *map_progress += delta;
- return (*map_progress);
-}
-
/*
* Copy data between ring buffers, handling wraparound.
* The copy starts at 'offset' and copies 'length' bytes.
@@ -169,8 +73,6 @@ main(int argc, char *argv[])
int ch, bytes;
int frag_size, frame_size, verbose = 0;
int map_pointer = 0;
- unsigned step_frames;
- int64_t frame_ns, start_ns, next_wakeup_ns;
int64_t read_progress = 0, write_progress = 0;
oss_syncgroup sync_group = { 0, 0, { 0 } };
struct config config_in = {
@@ -187,6 +89,8 @@ main(int argc, char *argv[])
.sample_rate = 48000,
.mmap = 1,
};
+ struct kevent ev;
+ int kq;
while ((ch = getopt(argc, argv, "v")) != -1) {
switch (ch) {
@@ -228,10 +132,6 @@ main(int argc, char *argv[])
errx(1,
"Input and output configurations have different fragment sizes");
- /* Calculate timing parameters */
- step_frames = frame_stepping(config_in.sample_rate);
- frame_ns = 1000000000LL / config_in.sample_rate;
-
/* Clear output buffer to prevent noise on startup */
memset(config_out.buf, 0, bytes);
@@ -245,25 +145,51 @@ main(int argc, char *argv[])
if (ioctl(config_in.fd, SNDCTL_DSP_SYNCSTART, &sync_group.id) < 0)
err(1, "Starting sync group failed");
- /* Initialize timing and progress tracking */
- start_ns = gettime_ns();
- read_progress = update_map_progress(config_in.fd, SNDCTL_DSP_GETIPTR,
- &map_pointer, &read_progress, bytes, frag_size, frame_size);
- write_progress = read_progress;
- next_wakeup_ns = start_ns;
+ /* Create kqueue and register input device for read events */
+ kq = kqueue();
+ if (kq < 0)
+ err(1, "kqueue failed");
+ EV_SET(&ev, config_in.fd, EVFILT_READ, EV_ADD, 0, 0, NULL);
+ if (kevent(kq, &ev, 1, NULL, 0, NULL) < 0)
+ err(1, "kevent register failed");
/*
* Main processing loop:
- * 1. Sleep until next scheduled wakeup
- * 2. Check how much new audio data is available
- * 3. Copy available data from input to output buffer
- * 4. Schedule next wakeup
+ * Block on kevent() until input data is available.
+ * ext[0] holds the current DMA pointer (GETIPTR/GETOPTR equivalent).
+ * ext[1] holds the xrun count for the channel (GETERROR equivalent).
*/
for (;;) {
- sleep_until_ns(next_wakeup_ns);
- read_progress = update_map_progress(config_in.fd,
- SNDCTL_DSP_GETIPTR, &map_pointer, &read_progress, bytes,
- frag_size, frame_size);
+ int n;
+ int ptr;
+ unsigned delta;
+
+ n = kevent(kq, NULL, 0, &ev, 1, NULL);
+ if (n < 0)
+ err(1, "kevent failed");
+ if (n == 0)
+ continue;
+
+ ptr = (int)ev.ext[0];
+ if (ptr < 0 || ptr >= bytes)
+ errx(1, "Pointer out of bounds: %d", ptr);
+ if ((ptr % frame_size) != 0)
+ errx(1, "Pointer %d not aligned to frame size %d", ptr,
+ frame_size);
+
+ /*
+ * Calculate delta: how many bytes have been processed since
+ * last check. Handle ring buffer wraparound.
+ */
+ delta = (ptr + bytes - map_pointer) % bytes;
+
+ /* Update pointer and progress tracking */
+ map_pointer = ptr;
+ read_progress += delta;
+
+ /* Report xruns if any */
+ if (ev.ext[1] != 0 && verbose)
+ warnx("xruns: %llu", (unsigned long long)ev.ext[1]);
/* Copy new audio data if available */
if (read_progress > write_progress) {
@@ -277,13 +203,9 @@ main(int argc, char *argv[])
printf("copied %d bytes at %d (abs %lld)\n",
length, offset, (long long)write_progress);
}
-
- /* Schedule next wakeup based on frame timing */
- next_wakeup_ns += (int64_t)step_frames * frame_ns;
- if (next_wakeup_ns < gettime_ns())
- next_wakeup_ns = gettime_ns();
}
+ close(kq);
if (munmap(config_in.buf, bytes) != 0)
err(1, "Memory unmap failed");
config_in.buf = NULL;