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// RX side of flow control -- when we are running out of RX space, send a PAUSE
module flow_ctrl_rx
(input pause_request_en, input [15:0] pause_time, input [15:0] pause_thresh,
input rx_clk, input rx_reset, input [15:0] rx_fifo_space,
input tx_clk, input tx_reset, output reg pause_req, output reg [15:0] pause_time_req
);
// ******************************************************************************
// Force our TX to send a PAUSE frame because our RX is nearly full
// ******************************************************************************
// RX Clock Domain
reg xon, xoff;
reg [21:0] countdown;
wire [15:0] pause_low_thresh = pause_thresh;
wire [15:0] pause_hi_thresh = 16'hFFFF;
wire [21:0] pq_reduced = {pause_time,6'd0} - 1700;
always @(posedge rx_clk)
if(rx_reset)
xoff <= 0;
else
xoff <= (pause_request_en & (countdown==0) & (rx_fifo_space < pause_low_thresh));
always @(posedge rx_clk)
if(rx_reset)
xon <= 0;
else
xon <= ((countdown!=0) & (rx_fifo_space > pause_hi_thresh));
always @(posedge rx_clk)
if(rx_reset)
countdown <= 0;
else if(xoff)
countdown <= pq_reduced;
else if(xon)
countdown <= 0;
else if(countdown != 0)
countdown <= countdown - 1;
// Cross clock domains
oneshot_2clk send_xon (.clk_in(rx_clk), .in(xon), .clk_out(tx_clk), .out(xon_tx));
oneshot_2clk send_xoff (.clk_in(rx_clk), .in(xoff), .clk_out(tx_clk), .out(xoff_tx));
always @(posedge tx_clk)
if(xoff_tx)
pause_time_req <= pause_time;
else if(xon_tx)
pause_time_req <= 0;
always @(posedge tx_clk)
if(tx_reset)
pause_req <= 0;
else
pause_req <= xon_tx | xoff_tx;
endmodule // flow_ctrl_rx
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