RFNoC: Prevent unnecessary FC ACK packets

Avoid sending flow control ACK packets for lossless transports.
Add 'send_no_fc_acks' device argument to explicitly prevent
flow control ACK packets from being sent.

Signed-off-by: michael-west <michael.west@ettus.com>

1 files changed, 8 insertions, 3 deletions

diff --git a/host/lib/usrp/device3/device3_io_impl.cpp b/host/lib/usrp/device3/device3_io_impl.cpp
index bf527e0ba..d0ec52971 100644
--- a/host/lib/usrp/device3/device3_io_impl.cpp
+++ b/host/lib/usrp/device3/device3_io_impl.cpp
@@ -731,9 +731,14 @@ tx_streamer::sptr device3_impl::get_tx_stream(const uhd::stream_args_t& args_)
         // CHDR does not support trailers
         my_streamer->set_enable_trailer(false);
 
-        my_streamer->set_xport_chan_post_send_cb(stream_i, [fc_cache, xport]() {
-            tx_flow_ctrl_ack(fc_cache, xport.send, xport.send_sid);
-        });
+        // Avoid sending FC ACKs if the transport is lossless or the user
+        // has explictly requested not to send them
+        if (not (xport.lossless or tx_hints.has_key("send_no_fc_acks")))
+        {
+            my_streamer->set_xport_chan_post_send_cb(stream_i, [fc_cache, xport]() {
+                tx_flow_ctrl_ack(fc_cache, xport.send, xport.send_sid);
+            });
+        }
     }
 
     // Notify all blocks in this chain that they are connected to an active streamer