RFNoC: Fix flush in source_block_ctrl_base

The configure_flow_control_out function was set to dump any packets
onto the crossbar, which could cause issues on the crossbar and in
downstream blocks.  Replacing wil a call to the _flush() function in
the block_ctrl_base parent class, which drops the packets so they do
not get put onto the crossbar.

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

2 files changed, 4 insertions, 21 deletions

diff --git a/host/include/uhd/rfnoc/block_ctrl_base.hpp b/host/include/uhd/rfnoc/block_ctrl_base.hpp
index 0bf701810..df3fab02e 100644
--- a/host/include/uhd/rfnoc/block_ctrl_base.hpp
+++ b/host/include/uhd/rfnoc/block_ctrl_base.hpp
@@ -372,6 +372,9 @@ protected:
     // than reset register SR_CLEAR_TX_FC.
     virtual void _clear(const size_t port = 0);
 
+    //! Flush any in-flight packets for this block
+    bool _flush(const size_t port = 0);
+
     //! Override this function if your block needs to specially handle
     // setting the command time
     virtual void _set_command_time(
@@ -404,9 +407,6 @@ private:
     //! Helper to start flushing for this block
     void _start_drain(const size_t port = 0);
 
-    //! Helper to flush any in-flight packets for this block
-    bool _flush(const size_t port = 0);
-
     /***********************************************************************
      * Private members
      **********************************************************************/
diff --git a/host/lib/rfnoc/source_block_ctrl_base.cpp b/host/lib/rfnoc/source_block_ctrl_base.cpp
index 656ab26af..994d66380 100644
--- a/host/lib/rfnoc/source_block_ctrl_base.cpp
+++ b/host/lib/rfnoc/source_block_ctrl_base.cpp
@@ -102,24 +102,7 @@ void source_block_ctrl_base::configure_flow_control_out(const bool enable_fc_out
                 % buf_size_bytes % unique_id()));
     }
 
-    // Disable flow control entirely and let all upstream data flush out
-    // We need to do this every time the window is changed because
-    // a) We don't know what state the flow-control module was left in
-    //   in the previous run (it should still be enabled)
-    // b) Changing the window size where data is buffered upstream may
-    //   result in stale packets entering the stream.
-    sr_write(SR_FLOW_CTRL_EN, 0, block_port);
-
-    // Wait for data to flush out.
-    // In the FPGA we are guaranteed that all buffered packets are more-or-less
-    // consecutive. 1ms@200MHz = 200,000 cycles of "flush time". 200k cycles = 200k * 8
-    // bytes (64 bits) = 1.6MB of data that can be flushed. Typically in the FPGA we have
-    // buffering in the order of kilobytes so waiting for 1MB to flush is more than enough
-    // time.
-    // TODO: Enhancement. We should get feedback from the FPGA about when the
-    // source_flow_control
-    //      module is done flushing.
-    std::this_thread::sleep_for(std::chrono::milliseconds(1));
+    _flush(block_port);
 
     // Enable source flow control module and conditionally enable byte based and/or packet
     // count based flow control