lib: change default number of transfers to 15

So far we had 32 * 256KB which was a bit overkill,
15 are more than enough.

15 was chosen instead of 16 because at least on Linux
there seems to be a system-wide limit of 63 transfers
(when they are 256KB large), so 4 dongles can be used
on a single machine without lowering the default transfer
number.

Signed-off-by: Steve Markgraf <steve@steve-m.de>

include/rtl-sdr.h

@@ -351,9 +351,10 @@ RTLSDR_API int rtlsdr_wait_async(rtlsdr_dev_t *dev, rtlsdr_read_async_cb_t cb, v
  * \param cb callback function to return received samples
  * \param ctx user specific context to pass via the callback function
  * \param buf_num optional buffer count, buf_num * buf_len = overall buffer size
- *		  set to 0 for default buffer count (32)
+ *		  set to 0 for default buffer count (15)
  * \param buf_len optional buffer length, must be multiple of 512,
- *		  set to 0 for default buffer length (16 * 32 * 512)
+ *		  should be a multiple of 16384 (URB size), set to 0
+ *		  for default buffer length (16 * 32 * 512)
  * \return 0 on success
  */
 RTLSDR_API int rtlsdr_read_async(rtlsdr_dev_t *dev,

src/librtlsdr.c

@@ -338,7 +338,7 @@ static rtlsdr_dongle_t known_devices[] = {
 	{ 0x1f4d, 0xd803, "PROlectrix DV107669" },
 };
 
-#define DEFAULT_BUF_NUMBER	32
+#define DEFAULT_BUF_NUMBER	15
 #define DEFAULT_BUF_LENGTH	(16 * 32 * 512)
 
 #define DEF_RTL_XTAL_FREQ	28800000

src/rtl_fm.c

@@ -76,7 +76,6 @@
 #include "convenience/convenience.h"
 
 #define DEFAULT_SAMPLE_RATE		24000
-#define DEFAULT_ASYNC_BUF_NUMBER	32
 #define DEFAULT_BUF_LENGTH		(1 * 16384)
 #define MAXIMUM_OVERSAMPLE		16
 #define MAXIMUM_BUF_LENGTH		(MAXIMUM_OVERSAMPLE * DEFAULT_BUF_LENGTH)
@@ -807,8 +806,7 @@ static void rtlsdr_callback(unsigned char *buf, uint32_t len, void *ctx)
 static void *dongle_thread_fn(void *arg)
 {
 	struct dongle_state *s = arg;
-	rtlsdr_read_async(s->dev, rtlsdr_callback, s,
-		DEFAULT_ASYNC_BUF_NUMBER, s->buf_len);
+	rtlsdr_read_async(s->dev, rtlsdr_callback, s, 0, s->buf_len);
 	return 0;
 }
 

src/rtl_sdr.c

@@ -35,7 +35,6 @@
 #include "convenience/convenience.h"
 
 #define DEFAULT_SAMPLE_RATE		2048000
-#define DEFAULT_ASYNC_BUF_NUMBER	32
 #define DEFAULT_BUF_LENGTH		(16 * 16384)
 #define MINIMAL_BUF_LENGTH		512
 #define MAXIMAL_BUF_LENGTH		(256 * 16384)
@@ -261,7 +260,7 @@ int main(int argc, char **argv)
 	} else {
 		fprintf(stderr, "Reading samples in async mode...\n");
 		r = rtlsdr_read_async(dev, rtlsdr_callback, (void *)file,
-				      DEFAULT_ASYNC_BUF_NUMBER, out_block_size);
+				      0, out_block_size);
 	}
 
 	if (do_exit)

src/rtl_tcp.c

@@ -92,7 +92,7 @@ void usage(void)
 		"\t[-f frequency to tune to [Hz]]\n"
 		"\t[-g gain (default: 0 for auto)]\n"
 		"\t[-s samplerate in Hz (default: 2048000 Hz)]\n"
-		"\t[-b number of buffers (default: 32, set by library)]\n"
+		"\t[-b number of buffers (default: 15, set by library)]\n"
 		"\t[-n max number of linked list buffers to keep (default: 500)]\n"
 		"\t[-d device index (default: 0)]\n"
 		"\t[-P ppm_error (default: 0)]\n");

src/rtl_test.c

@@ -44,7 +44,6 @@
 #include "convenience/convenience.h"
 
 #define DEFAULT_SAMPLE_RATE		2048000
-#define DEFAULT_ASYNC_BUF_NUMBER	32
 #define DEFAULT_BUF_LENGTH		(16 * 16384)
 #define MINIMAL_BUF_LENGTH		512
 #define MAXIMAL_BUF_LENGTH		(256 * 16384)
@@ -406,7 +405,7 @@ int main(int argc, char **argv)
 	} else {
 		fprintf(stderr, "Reading samples in async mode...\n");
 		r = rtlsdr_read_async(dev, rtlsdr_callback, NULL,
-				      DEFAULT_ASYNC_BUF_NUMBER, out_block_size);
+				      0, out_block_size);
 	}
 
 	if (do_exit) {