rfnoc: Implement overrun handling using action API

In order to enable overrun handling through the action API, a few new
features are implemented:
- The RX streamer can now accept stream command actions. The streamer
  will interpret stream command actions as a request to send stream
  commands upstream to all producers.
- A new action type is defined ('restart request') which is understood
  by the radio and streamer, and is a handshake between producers and
  consumers. In this case, it will ask the radio to send a stream
  command itself.

When an RX streamer receives an overrun, it will now run the following
algorithm:
1. Stop all upstream producers (this was already in the code before this
   commit).
2. If no restart is required, Wait for the radios to have space in the
   downstream blocks.

The radio, if it was in continuous streaming mode before the overrun,
includes a flag in its initial action whether or not to restart the
streaming. Also, it will wait for the stop stream command from the
streamer. When it receives that, it will initiate a restart request
handshake.

3. The streamer submits a restart request action upstream. This action
   will be received by the radio.
   The radio will then check the current time, and send a stream command
   action back downstream.
4. The RX streamer receives the stream command action, and uses it to
   send another stream command to all upstream producers. This way, all
   upstream producers receive a start command for the same time.

1 files changed, 3 insertions, 2 deletions

diff --git a/host/lib/rfnoc/graph.cpp b/host/lib/rfnoc/graph.cpp
index ff5fde1e9..1a25f84f9 100644
--- a/host/lib/rfnoc/graph.cpp
+++ b/host/lib/rfnoc/graph.cpp
@@ -417,8 +417,9 @@ void graph_t::enqueue_action(
         // The following call can cause other nodes to add more actions to
         // the end of _action_queue!
         UHD_LOG_TRACE(LOG_ID,
-            "Now delivering action " << next_action_sptr->key << "#"
-                                     << next_action_sptr->id);
+            "Now delivering action "
+                << next_action_sptr->key << "#" << next_action_sptr->id << " to "
+                << recipient_node->get_unique_id() << "@" << recipient_port.to_string());
         node_accessor_t{}.send_action(recipient_node, recipient_port, next_action_sptr);
     }
     UHD_LOG_TRACE(LOG_ID, "Delivered all actions, terminating action handling.");