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module fifo_short
#(parameter WIDTH=32)
(input clk, input reset, input clear,
input [WIDTH-1:0] datain,
input src_rdy_i,
output dst_rdy_o,
output [WIDTH-1:0] dataout,
output src_rdy_o,
input dst_rdy_i,
output reg [4:0] space,
output reg [4:0] occupied);
reg full, empty;
wire write = src_rdy_i & dst_rdy_o;
wire read = dst_rdy_i & src_rdy_o;
assign dst_rdy_o = ~full;
assign src_rdy_o = ~empty;
reg [3:0] a;
genvar i;
generate
for (i=0;i<WIDTH;i=i+1)
begin : gen_srl16
SRL16E
srl16e(.Q(dataout[i]),
.A0(a[0]),.A1(a[1]),.A2(a[2]),.A3(a[3]),
.CE(write),.CLK(clk),.D(datain[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 == 14)
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 <= 16;
else if(clear)
space <= 16;
else if(read & ~write)
space <= space + 1;
else if(write & ~read)
space <= space - 1;
always @(posedge clk)
if(reset)
occupied <= 0;
else if(clear)
occupied <= 0;
else if(read & ~write)
occupied <= occupied - 1;
else if(write & ~read)
occupied <= occupied + 1;
endmodule // fifo_short
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