added xon backpressure to flush tx stream when pause frames are received

by MAC

applications/lofar2/libraries/sdp/src/vhdl/sdp_station.vhd

@@ -1042,13 +1042,14 @@ BEGIN
     ---------------
     u_nw_10GbE_beamlet_output: ENTITY nw_10GbE_lib.nw_10GbE
     GENERIC MAP (
-      g_sim           => g_sim,
-      g_sim_level     => 1,
-      g_nof_macs      => c_nof_10GbE_beamlet_output,
-      g_direction     => "TX_RX",
-      g_tx_fifo_fill  => c_fifo_tx_fill_beamlet_output,
-      g_tx_fifo_size  => c_fifo_tx_size_beamlet_output,
-      g_ip_hdr_field_arr => c_sdp_cep_hdr_field_arr
+      g_sim              => g_sim,
+      g_sim_level        => 1,
+      g_nof_macs         => c_nof_10GbE_beamlet_output,
+      g_direction        => "TX_RX",
+      g_tx_fifo_fill     => c_fifo_tx_fill_beamlet_output,
+      g_tx_fifo_size     => c_fifo_tx_size_beamlet_output,
+      g_ip_hdr_field_arr => c_sdp_cep_hdr_field_arr,
+      g_xon_backpressure => TRUE
   
     )
     PORT MAP (

libraries/io/nw_10GbE/src/vhdl/nw_10GbE.vhd

@@ -52,6 +52,7 @@ ENTITY nw_10GbE IS
     g_tx_fifo_size           : NATURAL := 256;   -- 2 * 32b * 256 = 2 M9K (DP interface has 64b data, so at least 2 M9K needed)
     g_rx_fifo_size           : NATURAL := 256;   -- 2 * 32b * 256 = 2 M9K (DP interface has 64b data, so at least 2 M9K needed)
     g_word_alignment_padding : BOOLEAN := FALSE;
+    g_xon_backpressure       : BOOLEAN := FALSE;
     g_arp_period_s           : NATURAL := 30;
     g_ip_hdr_field_arr       : t_common_field_arr
   );
@@ -232,7 +233,8 @@ BEGIN
     g_tx_fifo_fill           => g_tx_fifo_fill, 
     g_tx_fifo_size           => g_tx_fifo_size, 
     g_rx_fifo_size           => g_rx_fifo_size, 
-    g_word_alignment_padding => g_word_alignment_padding 
+    g_word_alignment_padding => g_word_alignment_padding,
+    g_xon_backpressure       => g_xon_backpressure 
   )
   PORT MAP (
     -- Transceiver PLL reference clock

libraries/io/tr_10GbE/src/vhdl/tr_10GbE.vhd

@@ -45,6 +45,10 @@
 --
 --   to avoid that the packet transmission will get a gap that will abort it.
 --   The average DP data rate depends on dp_clk and on the DP data valid.
+--
+--   g_xon_backpressure can be enabled to set xon = 0 when the TX fill fifo is
+--   full. This also makes use of an extra fifo of size g_tx_fifo_size to 
+--   buffer the last incoming frame when xon = 0 to prevent corrupting the frame.
 --  
 
 LIBRARY IEEE, common_lib, dp_lib, diag_lib, technology_lib, tech_mac_10g_lib, tech_eth_10g_lib, tr_xaui_lib;
@@ -72,7 +76,8 @@ ENTITY tr_10GbE IS
     g_tx_fifo_fill           : NATURAL := 10;    -- Release tx packet only when sufficiently data is available, 
     g_tx_fifo_size           : NATURAL := 256;   -- 2 * 32b * 256 = 2 M9K (DP interface has 64b data, so at least 2 M9K needed)
     g_rx_fifo_size           : NATURAL := 256;   -- 2 * 32b * 256 = 2 M9K (DP interface has 64b data, so at least 2 M9K needed)
-    g_word_alignment_padding : BOOLEAN := FALSE
+    g_word_alignment_padding : BOOLEAN := FALSE;
+    g_xon_backpressure       : BOOLEAN := FALSE
   );
   PORT (
     -- Transceiver PLL reference clock
@@ -146,11 +151,12 @@ ARCHITECTURE str OF tr_10GbE IS
   SIGNAL eth_rx_clk_arr                 : STD_LOGIC_VECTOR(g_nof_macs-1 DOWNTO 0);
   SIGNAL eth_rx_rst_arr                 : STD_LOGIC_VECTOR(g_nof_macs-1 DOWNTO 0);
 
-  SIGNAL dp_fifo_dc_tx_src_out_arr      : t_dp_sosi_arr(g_nof_macs-1 DOWNTO 0); 
-  SIGNAL dp_fifo_dc_tx_src_in_arr       : t_dp_siso_arr(g_nof_macs-1 DOWNTO 0);
+  SIGNAL dp_fifo_sc_tx_src_out_arr      : t_dp_sosi_arr(g_nof_macs-1 DOWNTO 0); 
+  SIGNAL dp_fifo_sc_tx_src_in_arr       : t_dp_siso_arr(g_nof_macs-1 DOWNTO 0);
 
   SIGNAL dp_fifo_fill_tx_src_out_arr    : t_dp_sosi_arr(g_nof_macs-1 DOWNTO 0); 
   SIGNAL dp_fifo_fill_tx_src_in_arr     : t_dp_siso_arr(g_nof_macs-1 DOWNTO 0);
+  SIGNAL dp_fifo_fill_tx_snk_out_arr    : t_dp_siso_arr(g_nof_macs-1 DOWNTO 0);
 
   SIGNAL mac_10g_src_out_arr            : t_dp_sosi_arr(g_nof_macs-1 DOWNTO 0); 
   SIGNAL mac_10g_src_in_arr             : t_dp_siso_arr(g_nof_macs-1 DOWNTO 0);
@@ -227,7 +233,48 @@ BEGIN
     eth_rx_clk_arr    => eth_rx_clk_arr,
     eth_rx_rst_arr    => eth_rx_rst_arr
   );  
-  
+ 
+  ---------------------------------------------------------------------------------------
+  -- TX FIFO for buffering last packet when xon = 0 to prevent corrupt frames. 
+  ---------------------------------------------------------------------------------------
+  gen_xon_backpressure : IF g_xon_backpressure GENERATE
+    gen_dp_fifo_sc_tx : FOR i IN 0 TO g_nof_macs-1 GENERATE
+      u_dp_fifo_sc_tx : ENTITY dp_lib.dp_fifo_sc
+      GENERIC MAP (
+        g_technology  => g_technology,
+        g_data_w      => c_xgmii_data_w,
+        g_empty_w     => c_tech_mac_10g_empty_w,
+        g_use_empty   => TRUE,
+        g_fifo_size   => g_tx_fifo_size
+      )
+      PORT MAP (
+        rst         => dp_rst,
+        clk         => dp_clk,
+    
+        snk_out     => snk_out_arr(i),
+        snk_in      => snk_in_arr(i),
+    
+        src_in      => dp_fifo_sc_tx_src_in_arr(i), 
+        src_out     => dp_fifo_sc_tx_src_out_arr(i)
+      );   
+    END GENERATE;
+
+    -- When MAC receives pause frames, it's ready signal is low for a long time
+    -- Set xon to (xon AND ready) to enable flushing frames using external dp_xonoff.
+    p_fifo_sc_tx : PROCESS(dp_fifo_fill_tx_snk_out_arr)
+    BEGIN
+      dp_fifo_sc_tx_src_in_arr <= dp_fifo_fill_tx_snk_out_arr;
+      FOR i IN 0 TO g_nof_macs-1 LOOP
+        dp_fifo_sc_tx_src_in_arr(i).xon <= dp_fifo_fill_tx_snk_out_arr(i).xon AND dp_fifo_fill_tx_snk_out_arr(i).ready;
+      END LOOP;
+    END PROCESS;
+  END GENERATE;
+
+  gen_no_xon_backpressure : IF NOT g_xon_backpressure GENERATE
+    dp_fifo_sc_tx_src_out_arr <= snk_in_arr;
+    snk_out_arr <= dp_fifo_fill_tx_snk_out_arr;
+  END GENERATE;
+ 
   ---------------------------------------------------------------------------------------
   -- TX: FIFO: dp_clk -> tx_clk and with fill level/eop trigger so we can deliver packets to the MAC fast enough
   ---------------------------------------------------------------------------------------
@@ -248,19 +295,17 @@ BEGIN
       rd_rst      => eth_tx_rst_arr(i),
       rd_clk      => eth_tx_clk_arr(i),
 
-      snk_out     => snk_out_arr(i),
-      snk_in      => snk_in_arr(i),
+      snk_out     => dp_fifo_fill_tx_snk_out_arr(i),
+      snk_in      => dp_fifo_sc_tx_src_out_arr(i),
 
       src_in      => dp_fifo_fill_tx_src_in_arr(i),
       src_out     => dp_fifo_fill_tx_src_out_arr(i)
     );
   END GENERATE;
   
-  
   ---------------------------------------------------------------------------------------
   -- ETH MAC + PHY
   ---------------------------------------------------------------------------------------
-
   u_tech_eth_10g : ENTITY tech_eth_10g_lib.tech_eth_10g
   GENERIC MAP (
     g_technology          => g_technology,