From 8041472ff783d23cd2ae1c001fa3e6dab9b01982 Mon Sep 17 00:00:00 2001
From: Dimitri Stolnikov <horiz0n@gmx.net>
Date: Wed, 28 Nov 2012 20:44:43 +0100
Subject: [PATCH] rtl: introduce buflen argument

this might be helful for rates <1MSPS
value must be multiple of 512 bytes
---
 lib/rtl/rtl_source_c.cc | 35 ++++++++++++++++++++++-------------
 lib/rtl/rtl_source_c.h  |  1 +
 2 files changed, 23 insertions(+), 13 deletions(-)

diff --git a/lib/rtl/rtl_source_c.cc b/lib/rtl/rtl_source_c.cc
index 8016e34..efa28fa 100644
--- a/lib/rtl/rtl_source_c.cc
+++ b/lib/rtl/rtl_source_c.cc
@@ -44,7 +44,7 @@
 
 using namespace boost::assign;
 
-#define BUF_SIZE  (16 * 32 * 512)
+#define BUF_LEN  (16 * 32 * 512) /* must be multiple of 512 */
 #define BUF_NUM   32
 #define BUF_SKIP  1 // buffers to skip due to initial garbage
 
@@ -143,18 +143,27 @@ rtl_source_c::rtl_source_c (const std::string &args)
   if (dict.count("offset_tune"))
     offset_tune = boost::lexical_cast< unsigned int >( dict["offset_tune"] );
 
-  _buf_num = BUF_NUM;
-  _buf_head = _buf_used = _buf_offset = 0;
-  _samp_avail = BUF_SIZE / BYTES_PER_SAMPLE;
+  _buf_num = _buf_len = _buf_head = _buf_used = _buf_offset = 0;
 
-  if (dict.count("buffers")) {
-    _buf_num = (unsigned int)boost::lexical_cast< double >( dict["buffers"] );
-    if (0 == _buf_num)
-      _buf_num = BUF_NUM;
-    std::cerr << "Using " << _buf_num << " buffers of size " << BUF_SIZE << "."
+  if (dict.count("buffers"))
+    _buf_num = boost::lexical_cast< unsigned int >( dict["buffers"] );
+
+  if (dict.count("buflen"))
+    _buf_len = boost::lexical_cast< unsigned int >( dict["buflen"] );
+
+  if (0 == _buf_num)
+    _buf_num = BUF_NUM;
+
+  if (0 == _buf_len || _buf_len % 512 != 0) /* len must be multiple of 512 */
+    _buf_len = BUF_LEN;
+
+  if ( BUF_NUM != _buf_num || BUF_LEN != _buf_len ) {
+    std::cerr << "Using " << _buf_num << " buffers of size " << _buf_len << "."
               << std::endl;
   }
 
+  _samp_avail = _buf_len / BYTES_PER_SAMPLE;
+
   // create a lookup table for gr_complex values
   for (unsigned int i = 0; i <= 0xffff; i++) {
 #ifdef BOOST_LITTLE_ENDIAN
@@ -198,7 +207,7 @@ rtl_source_c::rtl_source_c (const std::string &args)
   if (direct_samp) {
     ret = rtlsdr_set_direct_sampling(_dev, direct_samp);
     if (ret < 0)
-      throw std::runtime_error("Failed to enable direct sampling mode.");
+      throw std::runtime_error("Failed to enable direct sampling.");
   }
 
   if (offset_tune) {
@@ -217,7 +226,7 @@ rtl_source_c::rtl_source_c (const std::string &args)
 
   if (_buf) {
     for(unsigned int i = 0; i < _buf_num; ++i)
-      _buf[i] = (unsigned short *) malloc(BUF_SIZE);
+      _buf[i] = (unsigned short *) malloc(_buf_len);
   }
 
   _thread = gruel::thread(_rtlsdr_wait, this);
@@ -284,7 +293,7 @@ void rtl_source_c::_rtlsdr_wait(rtl_source_c *obj)
 
 void rtl_source_c::rtlsdr_wait()
 {
-  int ret = rtlsdr_read_async( _dev, _rtlsdr_callback, (void *)this, 0, BUF_SIZE );
+  int ret = rtlsdr_read_async( _dev, _rtlsdr_callback, (void *)this, 0, _buf_len );
 
   _running = false;
 
@@ -335,7 +344,7 @@ int rtl_source_c::work( int noutput_items,
       *out++ = _lut[ *(buf + i) ];
 
     _buf_offset = remaining;
-    _samp_avail = (BUF_SIZE / BYTES_PER_SAMPLE) - remaining;
+    _samp_avail = (_buf_len / BYTES_PER_SAMPLE) - remaining;
   }
 
   return noutput_items;
diff --git a/lib/rtl/rtl_source_c.h b/lib/rtl/rtl_source_c.h
index 5f4ccdd..fd2395c 100644
--- a/lib/rtl/rtl_source_c.h
+++ b/lib/rtl/rtl_source_c.h
@@ -124,6 +124,7 @@ private:
   gruel::thread _thread;
   unsigned short **_buf;
   unsigned int _buf_num;
+  unsigned int _buf_len;
   unsigned int _buf_head;
   unsigned int _buf_used;
   boost::mutex _buf_mutex;