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//
// Copyright 2012-2013 Ettus Research LLC
// Copyright 2018 Ettus Research, a National Instruments Company
//
// SPDX-License-Identifier: LGPL-3.0-or-later
//
// Block RAM AXI fifo
// Special case SIZE <= 5 uses a short fifo
module axi_fifo_legacy
#(parameter WIDTH=32, SIZE=9)
(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 [15:0] space,
output reg [15:0] occupied);
generate
if(SIZE<=5) begin
wire [5:0] space_short, occupied_short;
axi_fifo_short #(.WIDTH(WIDTH)) fifo_short
(
.clk(clk), .reset(reset), .clear(clear),
.i_tdata(i_tdata), .i_tvalid(i_tvalid), .i_tready(i_tready),
.o_tdata(o_tdata), .o_tvalid(o_tvalid), .o_tready(o_tready),
.space(space_short), .occupied(occupied_short)
);
always @* space <= {10'b0, space_short};
always @* occupied <= {10'b0, occupied_short};
end
else begin
wire write = i_tvalid & i_tready;
wire read = o_tvalid & o_tready;
wire full, empty;
assign i_tready = ~full;
assign o_tvalid = ~empty;
// Read side states
localparam EMPTY = 0;
localparam PRE_READ = 1;
localparam READING = 2;
reg [SIZE-1:0] wr_addr, rd_addr;
reg [1:0] read_state;
reg empty_reg = 1'b1, full_reg = 1'b0;
always @(posedge clk)
if(reset)
wr_addr <= 0;
else if(clear)
wr_addr <= 0;
else if(write)
wr_addr <= wr_addr + 1;
ram_2port #(.DWIDTH(WIDTH),.AWIDTH(SIZE))
ram (.clka(clk),
.ena(1'b1),
.wea(write),
.addra(wr_addr),
.dia(i_tdata),
.doa(),
.clkb(clk),
.enb((read_state==PRE_READ)|read),
.web(1'b0),
.addrb(rd_addr),
.dib({WIDTH{1'b1}}),
.dob(o_tdata));
always @(posedge clk)
if(reset)
begin
read_state <= EMPTY;
rd_addr <= 0;
empty_reg <= 1;
end
else
if(clear)
begin
read_state <= EMPTY;
rd_addr <= 0;
empty_reg <= 1;
end
else
case(read_state)
EMPTY :
if(write)
begin
//rd_addr <= wr_addr;
read_state <= PRE_READ;
end
PRE_READ :
begin
read_state <= READING;
empty_reg <= 0;
rd_addr <= rd_addr + 1;
end
READING :
if(read)
if(rd_addr == wr_addr)
begin
empty_reg <= 1;
if(write)
read_state <= PRE_READ;
else
read_state <= EMPTY;
end
else
rd_addr <= rd_addr + 1;
endcase // case(read_state)
wire [SIZE-1:0] dont_write_past_me = rd_addr - 2;
wire becoming_full = wr_addr == dont_write_past_me;
always @(posedge clk)
if(reset)
full_reg <= 0;
else if(clear)
full_reg <= 0;
else if(read & ~write)
full_reg <= 0;
//else if(write & ~read & (wr_addr == (rd_addr-3)))
else if(write & ~read & becoming_full)
full_reg <= 1;
//assign empty = (read_state != READING);
assign empty = empty_reg;
// assign full = ((rd_addr - 1) == wr_addr);
assign full = full_reg;
//////////////////////////////////////////////
// space and occupied are for diagnostics only
// not guaranteed exact
localparam NUMLINES = (1<<SIZE);
always @(posedge clk)
if(reset)
space <= NUMLINES;
else if(clear)
space <= NUMLINES;
else if(read & ~write)
space <= space + 16'b1;
else if(write & ~read)
space <= space - 16'b1;
always @(posedge clk)
if(reset)
occupied <= 16'b0;
else if(clear)
occupied <= 16'b0;
else if(read & ~write)
occupied <= occupied - 16'b1;
else if(write & ~read)
occupied <= occupied + 16'b1;
end
endgenerate
endmodule // axi_fifo_legacy
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