2 // RX side of flow control -- when we are running out of RX space, send a PAUSE
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5 (input pause_request_en, input [15:0] pause_time, input [15:0] pause_thresh,
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6 input rx_clk, input rx_reset, input [15:0] rx_fifo_space,
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7 input tx_clk, input tx_reset, output reg pause_req, output reg [15:0] pause_time_req
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10 // ******************************************************************************
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11 // Force our TX to send a PAUSE frame because our RX is nearly full
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12 // ******************************************************************************
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16 reg [21:0] countdown;
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18 wire [15:0] pause_low_thresh = pause_thresh;
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19 wire [15:0] pause_hi_thresh = 16'hFFFF;
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20 wire [21:0] pq_reduced = {pause_time,6'd0} - 1700;
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22 always @(posedge rx_clk)
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26 xoff <= (pause_request_en & (countdown==0) & (rx_fifo_space < pause_low_thresh));
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28 always @(posedge rx_clk)
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32 xon <= ((countdown!=0) & (rx_fifo_space > pause_hi_thresh));
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34 always @(posedge rx_clk)
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38 countdown <= pq_reduced;
\r
41 else if(countdown != 0)
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42 countdown <= countdown - 1;
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44 // Cross clock domains
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45 oneshot_2clk send_xon (.clk_in(rx_clk), .in(xon), .clk_out(tx_clk), .out(xon_tx));
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46 oneshot_2clk send_xoff (.clk_in(rx_clk), .in(xoff), .clk_out(tx_clk), .out(xoff_tx));
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48 always @(posedge tx_clk)
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50 pause_time_req <= pause_time;
\r
52 pause_time_req <= 0;
\r
54 always @(posedge tx_clk)
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58 pause_req <= xon_tx | xoff_tx;
\r
60 endmodule // flow_ctrl_rx
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