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+//
+// Copyright 2011 Ettus Research LLC
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <http://www.gnu.org/licenses/>.
+//
+
+
+////////////////////////////////////////////////////////////////////////
+// Ethernet TX - Realign
+//
+// - removes a 2-byte pad from the front a fifo36 stream
+// - occupancy is preserved
+//
+
+module ethtx_realign
+ (input clk, input reset, input clear,
+ input [35:0] datain, input src_rdy_i, output dst_rdy_o,
+ output [35:0] dataout, output src_rdy_o, input dst_rdy_i);
+
+ reg [1:0] state;
+ reg [15:0] held;
+ reg [1:0] held_occ;
+ reg held_sof;
+
+ wire xfer_in = src_rdy_i & dst_rdy_o;
+ wire xfer_out = src_rdy_o & dst_rdy_i;
+
+ wire sof_in = datain[32];
+ wire eof_in = datain[33];
+ wire [1:0] occ_in = datain[35:34];
+ wire occ_low = occ_in[1] ^ occ_in[0]; //occ is 1 or 2
+
+ always @(posedge clk)
+ if(reset | clear)
+ begin
+ held <= 0;
+ held_occ <= 0;
+ held_sof <= 0;
+ end
+ else if(xfer_in)
+ begin
+ held <= datain[15:0];
+ held_occ <= occ_in;
+ held_sof <= sof_in;
+ end
+
+ localparam RE_IDLE = 0;
+ localparam RE_HELD = 1;
+ localparam RE_DONE = 2;
+
+ always @(posedge clk)
+ if(reset | clear)
+ state <= RE_IDLE;
+ else
+ case(state)
+ RE_IDLE :
+ if(xfer_in & eof_in)
+ state <= RE_DONE;
+ else if(xfer_in & sof_in)
+ state <= RE_HELD;
+
+ RE_HELD :
+ if(xfer_in & xfer_out & eof_in)
+ if(occ_low)
+ state <= RE_IDLE;
+ else
+ state <= RE_DONE;
+
+ RE_DONE :
+ if(xfer_out)
+ state <= RE_IDLE;
+
+ endcase // case (state)
+
+ wire sof_out = held_sof;
+ wire eof_out = (state == RE_HELD)? (eof_in & occ_low) : (state == RE_DONE);
+ wire [1:0] occ_out = ((state == RE_DONE)? held_occ : occ_in) ^ 2'b10; //(occ + 2)%4
+
+ assign dataout = {occ_out,eof_out,sof_out,held,datain[31:16]};
+ assign src_rdy_o = (state == RE_HELD)? src_rdy_i : (state == RE_DONE);
+ assign dst_rdy_o = (state == RE_HELD)? dst_rdy_i : (state == RE_IDLE);
+
+endmodule // ethtx_realign