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//
// Copyright 2012 Ettus Research LLC
//
//
// 32 word FIFO with AXI4-STREAM interface.
//
// NOTE: This module uses the SRLC32E primitive explicitly and as such
// can only be used with Xilinx technology of the VIRTEX-6/SPARTAN-6/SIERIES-7 or newer.
//
module axi_fifo_short
#(parameter WIDTH=32)
(
input clk,
input reset,
input clear,
input [WIDTH-1:0] i_tdata,
input i_tvalid,
output i_tready,
output [WIDTH-1:0] o_tdata,
output o_tvalid,
input o_tready,
output reg [5:0] space,
output reg [5:0] occupied
);
reg full, empty;
wire write = i_tvalid & i_tready;
wire read = o_tready & o_tvalid;
assign i_tready = ~full;
assign o_tvalid = ~empty;
reg [4:0] a;
genvar i;
generate
for (i=0;i<WIDTH;i=i+1)
begin : gen_srlc32e
SRLC32E
srlc32e(.Q(o_tdata[i]), .Q31(),
.A(a), //.A0(a[0]),.A1(a[1]),.A2(a[2]),.A3(a[3]),.A4(a[4]),
.CE(write),.CLK(clk),.D(i_tdata[i]));
end
endgenerate
always @(posedge clk)
if(reset)
begin
a <= 0;
empty <= 1;
full <= 0;
end
else if(clear)
begin
a <= 0;
empty <= 1;
full<= 0;
end
else if(read & ~write)
begin
full <= 0;
if(a==0)
empty <= 1;
else
a <= a - 1;
end
else if(write & ~read)
begin
empty <= 0;
if(~empty)
a <= a + 1;
if(a == 30)
full <= 1;
end
// NOTE will fail if you write into a full fifo or read from an empty one
//////////////////////////////////////////////////////////////
// space and occupied are used for diagnostics, not
// guaranteed correct
//assign space = full ? 0 : empty ? 16 : 15-a;
//assign occupied = empty ? 0 : full ? 16 : a+1;
always @(posedge clk)
if(reset)
space <= 6'd32;
else if(clear)
space <= 6'd32;
else if(read & ~write)
space <= space + 6'd1;
else if(write & ~read)
space <= space - 6'd1;
always @(posedge clk)
if(reset)
occupied <= 6'd0;
else if(clear)
occupied <= 6'd0;
else if(read & ~write)
occupied <= occupied - 6'd1;
else if(write & ~read)
occupied <= occupied + 6'd1;
endmodule // axi_fifo_short
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