3 files changed, 36 insertions, 18 deletions

diff --git a/gnuradio-core/src/lib/runtime/gr_block.cc b/gnuradio-core/src/lib/runtime/gr_block.cc
index fd82ab580..f52f7a6ba 100644
--- a/gnuradio-core/src/lib/runtime/gr_block.cc
+++ b/gnuradio-core/src/lib/runtime/gr_block.cc
@@ -31,8 +31,8 @@
 #include <gr_block_registry.h>
 
 gr_block::gr_block (const std::string &name,
-		    gr_io_signature_sptr input_signature,
-		    gr_io_signature_sptr output_signature)
+                    gr_io_signature_sptr input_signature,
+                    gr_io_signature_sptr output_signature)
   : gr_basic_block(name, input_signature, output_signature),
     d_output_multiple (1),
     d_output_multiple_set(false),
@@ -43,6 +43,7 @@ gr_block::gr_block (const std::string &name,
     d_fixed_rate(false),
     d_max_noutput_items_set(false),
     d_max_noutput_items(0),
+    d_min_noutput_items(0),
     d_tag_propagation_policy(TPP_ALL_TO_ALL),
     d_max_output_buffer(std::max(output_signature->max_streams(),1), -1),
     d_min_output_buffer(std::max(output_signature->max_streams(),1), -1)
diff --git a/gnuradio-core/src/lib/runtime/gr_block.h b/gnuradio-core/src/lib/runtime/gr_block.h
index c9d2d8f53..bd9ff42df 100644
--- a/gnuradio-core/src/lib/runtime/gr_block.h
+++ b/gnuradio-core/src/lib/runtime/gr_block.h
@@ -252,13 +252,30 @@ class GR_CORE_API gr_block : public gr_basic_block {
   void set_tag_propagation_policy(tag_propagation_policy_t p);
 
   /*!
+   * \brief Return the minimum number of output items this block can
+   * produce during a call to work.
+   *
+   * Should be 0 for most blocks.  Useful if we're dealing with packets and
+   * the block produces one packet per call to work.
+  */
+  int min_noutput_items() const { return d_min_noutput_items; }
+
+  /*!
+   * \brief Set the minimum number of output items this block can
+   * produce during a call to work.
+   *
+   * \param m the minimum noutput_items this block can produce.
+   */
+  void set_min_noutput_items(int m) { d_min_noutput_items = m; }
+
+  /*!
    * \brief Return the maximum number of output items this block will
    * handle during a call to work.
    */
   int max_noutput_items();
 
   /*!
-   * \brief Set the maximum number of ouput items htis block will
+   * \brief Set the maximum number of output items this block will
    * handle during a call to work.
    *
    * \param m the maximum noutput_items this block will handle.
@@ -428,6 +445,7 @@ class GR_CORE_API gr_block : public gr_basic_block {
   gr_block_detail_sptr	d_detail;		// implementation details
   unsigned              d_history;
   bool                  d_fixed_rate;
+  int                   d_min_noutput_items;
   bool                  d_max_noutput_items_set;     // if d_max_noutput_items is valid
   int                   d_max_noutput_items;         // value of max_noutput_items for this block
   tag_propagation_policy_t d_tag_propagation_policy; // policy for moving tags downstream
diff --git a/gnuradio-core/src/lib/runtime/gr_block_executor.cc b/gnuradio-core/src/lib/runtime/gr_block_executor.cc
index ee0ab9e37..27f591452 100644
--- a/gnuradio-core/src/lib/runtime/gr_block_executor.cc
+++ b/gnuradio-core/src/lib/runtime/gr_block_executor.cc
@@ -64,22 +64,21 @@ round_down (unsigned int n, unsigned int multiple)
 // on is done.
 //
 static int
-min_available_space (gr_block_detail *d, int output_multiple)
+min_available_space (gr_block_detail *d, int output_multiple, int min_noutput_items)
 {
-  int	min_space = std::numeric_limits<int>::max();
-
+  int min_space = std::numeric_limits<int>::max();
+  if (min_noutput_items == 0)
+    min_noutput_items = 1;
   for (int i = 0; i < d->noutputs (); i++){
     gruel::scoped_lock guard(*d->output(i)->mutex());
-#if 0
-    int n = round_down(d->output(i)->space_available(), output_multiple);
-#else
-    int n = round_down(std::min(d->output(i)->space_available(),
-				d->output(i)->bufsize()/2),
-		       output_multiple);
-#endif
-    if (n == 0){			// We're blocked on output.
-      if (d->output(i)->done()){	// Downstream is done, therefore we're done.
-	return -1;
+    int avail_n = round_down(d->output(i)->space_available(), output_multiple);
+    int best_n = round_down(d->output(i)->bufsize()/2, output_multiple);
+    if (best_n < min_noutput_items)
+      throw std::runtime_error("Buffer too small for min_noutput_items");
+    int n = std::min(avail_n, best_n);
+    if (n < min_noutput_items){  // We're blocked on output.
+      if (d->output(i)->done()){ // Downstream is done, therefore we're done.
+        return -1;
       }
       return 0;
     }
@@ -205,7 +204,7 @@ gr_block_executor::run_one_iteration()
     d_start_nitems_read.resize(0);
 
     // determine the minimum available output space
-    noutput_items = min_available_space (d, m->output_multiple ());
+    noutput_items = min_available_space (d, m->output_multiple (), m->min_noutput_items ());
     noutput_items = std::min(noutput_items, max_noutput_items);
     LOG(*d_log << " source\n  noutput_items = " << noutput_items << std::endl);
     if (noutput_items == -1)		// we're done
@@ -286,7 +285,7 @@ gr_block_executor::run_one_iteration()
     }
 
     // determine the minimum available output space
-    noutput_items = min_available_space (d, m->output_multiple ());
+    noutput_items = min_available_space (d, m->output_multiple (), m->min_noutput_items ());
     if (ENABLE_LOGGING){
       *d_log << " regular ";
       if (m->relative_rate() >= 1.0)