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////////////////////////////////////////////////////////////////////////
// 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
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