The enclosed diff adds a synchronous mode to rtl_fm. This helps
OpenBSD (where libusb async isn't yet working).

Signed-off-by: Stuart Henderson <stu@spacehopper.org>
---
src/rtl_fm.c | 29 +++++++++++++++++++++++++----
1 file changed, 25 insertions(+), 4 deletions(-)

diff --git a/src/rtl_fm.c b/src/rtl_fm.c
index e8ebb77..a71e287 100644
--- a/src/rtl_fm.c
+++ b/src/rtl_fm.c
@@ -128,6 +128,7 @@ void usage(void)
        "\t[-E sets lower edge tuning (default: center)]\n"
        "\t[-N enables NBFM mode (default: on)]\n"
        "\t[-W enables WBFM mode (default: off)]\n"
+        "\t[-S force sync output (default: async)]\n"
        "\t (-N -s 170k -o 4 -A fast -r 32k -l 0 -D)\n"
        "\tfilename (a '-' dumps samples to stdout)\n"
        "\t (omitting the filename also uses stdout)\n\n"
@@ -723,12 +724,14 @@ int main(int argc, char **argv)
    uint32_t dev_index = 0;
    int device_count;
    int ppm_error = 0;
+    int sync_mode = 0;
    char vendor[256], product[256], serial[256];
+
    fm_init(&fm);
    pthread_mutex_init(&data_ready, NULL);
    pthread_mutex_init(&data_write, NULL);

-    while ((opt = getopt(argc, argv, "d:f:g:s:b:l:o:t:r:p:EFA:NWMULRDC")) != -1) {
+    while ((opt = getopt(argc, argv, "d:f:g:s:b:l:o:t:r:p:EFA:NWMULRDSC")) != -1) {
        switch (opt) {
        case 'd':
            dev_index = atoi(optarg);
@@ -815,6 +818,9 @@ int main(int argc, char **argv)
        case 'R':
            fm.mode_demod = &raw_demod;
            break;
+        case 'S':
+            sync_mode = 1;
+            break;
        default:
            usage();
            break;
@@ -921,9 +927,24 @@ int main(int argc, char **argv)
        fprintf(stderr, "WARNING: Failed to reset buffers.\n");}

    pthread_create(&demod_thread, NULL, demod_thread_fn, (void *)(&fm));
-    rtlsdr_read_async(dev, rtlsdr_callback, (void *)(&fm),
-            DEFAULT_ASYNC_BUF_NUMBER,
-            lcm_post[fm.post_downsample] * DEFAULT_BUF_LENGTH);
+    if (sync_mode) {
+        fprintf(stderr, "Reading samples in sync mode...\n");
+        while (!do_exit) {
+            r = rtlsdr_read_sync(dev, &fm.buf,
+                       lcm_post[fm.post_downsample] * DEFAULT_BUF_LENGTH,
+                       &fm.buf_len);
+            if (r < 0) {
+                fprintf(stderr, "WARNING: sync read failed.\n");
+                break;
+            }
+            full_demod(&fm);
+        }
+    } else {
+        fprintf(stderr, "Reading samples in async mode...\n");
+        rtlsdr_read_async(dev, rtlsdr_callback, (void *)(&fm),
+                DEFAULT_ASYNC_BUF_NUMBER,
+                lcm_post[fm.post_downsample] * DEFAULT_BUF_LENGTH);
+    }

    if (do_exit) {
        fprintf(stderr, "\nUser cancel, exiting...\n");}
--
1.8.1.3