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/*
Copyright (c) 2015-2016 Alex Forencich
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/
// Language: Verilog 2001
`timescale 1ns / 1ps
/*
* Content Addressable Memory (shift register based)
*/
module cam_srl #(
// search data bus width
parameter DATA_WIDTH = 64,
// memory size in log2(words)
parameter ADDR_WIDTH = 5,
// width of data bus slices (4 for SRL16, 5 for SRL32)
parameter SLICE_WIDTH = 4
)
(
input wire clk,
input wire rst,
input wire [ADDR_WIDTH-1:0] write_addr,
input wire [DATA_WIDTH-1:0] write_data,
input wire write_delete,
input wire write_enable,
output wire write_busy,
input wire [DATA_WIDTH-1:0] compare_data,
output wire [2**ADDR_WIDTH-1:0] match_many,
output wire [2**ADDR_WIDTH-1:0] match_single,
output wire [ADDR_WIDTH-1:0] match_addr,
output wire match
);
// total number of slices (enough to cover DATA_WIDTH with address inputs)
localparam SLICE_COUNT = (DATA_WIDTH + SLICE_WIDTH - 1) / SLICE_WIDTH;
// depth of RAMs
localparam RAM_DEPTH = 2**ADDR_WIDTH;
localparam [1:0]
STATE_INIT = 2'd0,
STATE_IDLE = 2'd1,
STATE_WRITE = 2'd2,
STATE_DELETE = 2'd3;
reg [1:0] state_reg = STATE_INIT, state_next;
wire [SLICE_COUNT*SLICE_WIDTH-1:0] compare_data_padded = {{SLICE_COUNT*SLICE_WIDTH-DATA_WIDTH{1'b0}}, compare_data};
wire [SLICE_COUNT*SLICE_WIDTH-1:0] write_data_padded = {{SLICE_COUNT*SLICE_WIDTH-DATA_WIDTH{1'b0}}, write_data};
reg [SLICE_WIDTH-1:0] count_reg = {SLICE_WIDTH{1'b1}}, count_next;
reg [SLICE_COUNT-1:0] shift_data;
reg [RAM_DEPTH-1:0] shift_en;
reg [ADDR_WIDTH-1:0] write_addr_reg = {ADDR_WIDTH{1'b0}}, write_addr_next;
reg [SLICE_COUNT*SLICE_WIDTH-1:0] write_data_padded_reg = {SLICE_COUNT*SLICE_WIDTH{1'b0}}, write_data_padded_next;
reg write_busy_reg = 1'b1;
assign write_busy = write_busy_reg;
reg [RAM_DEPTH-1:0] match_raw_out[SLICE_COUNT-1:0];
reg [RAM_DEPTH-1:0] match_many_raw;
reg [RAM_DEPTH-1:0] match_many_reg = {RAM_DEPTH{1'b0}};
assign match_many = match_many_reg;
integer k;
always @* begin
match_many_raw = ~shift_en;
for (k = 0; k < SLICE_COUNT; k = k + 1) begin
match_many_raw = match_many_raw & match_raw_out[k];
end
end
cam_priority_encoder #(
.WIDTH(RAM_DEPTH),
.LSB_PRIORITY("HIGH")
)
priority_encoder_inst (
.input_unencoded(match_many_reg),
.output_valid(match),
.output_encoded(match_addr),
.output_unencoded(match_single)
);
integer i;
// SRLs
genvar row_ind, slice_ind;
generate
for (row_ind = 0; row_ind < RAM_DEPTH; row_ind = row_ind + 1) begin : row
for (slice_ind = 0; slice_ind < SLICE_COUNT; slice_ind = slice_ind + 1) begin : slice
reg [2**SLICE_WIDTH-1:0] srl_mem = {2**SLICE_WIDTH{1'b0}};
// match
always @* begin
match_raw_out[slice_ind][row_ind] = srl_mem[compare_data_padded[SLICE_WIDTH * slice_ind +: SLICE_WIDTH]];
end
// write
always @(posedge clk) begin
if (shift_en[row_ind]) begin
srl_mem <= {srl_mem[2**SLICE_WIDTH-2:0], shift_data[slice_ind]};
end
end
end
end
endgenerate
// match
always @(posedge clk) begin
match_many_reg <= match_many_raw;
end
// write
always @* begin
state_next = STATE_IDLE;
count_next = count_reg;
shift_data = {SLICE_COUNT{1'b0}};
shift_en = {RAM_DEPTH{1'b0}};
write_addr_next = write_addr_reg;
write_data_padded_next = write_data_padded_reg;
case (state_reg)
STATE_INIT: begin
// zero out shift registers
shift_en = {RAM_DEPTH{1'b1}};
shift_data = {SLICE_COUNT{1'b0}};
if (count_reg == 0) begin
state_next = STATE_IDLE;
end else begin
count_next = count_reg - 1;
state_next = STATE_INIT;
end
end
STATE_IDLE: begin
if (write_enable) begin
write_addr_next = write_addr;
write_data_padded_next = write_data_padded;
count_next = {SLICE_WIDTH{1'b1}};
if (write_delete) begin
state_next = STATE_DELETE;
end else begin
state_next = STATE_WRITE;
end
end else begin
state_next = STATE_IDLE;
end
end
STATE_WRITE: begin
// write entry
shift_en = 1'b1 << write_addr;
for (i = 0; i < SLICE_COUNT; i = i + 1) begin
shift_data[i] = count_reg == write_data_padded_reg[SLICE_WIDTH * i +: SLICE_WIDTH];
end
if (count_reg == 0) begin
state_next = STATE_IDLE;
end else begin
count_next = count_reg - 1;
state_next = STATE_WRITE;
end
end
STATE_DELETE: begin
// delete entry
shift_en = 1'b1 << write_addr;
shift_data = {SLICE_COUNT{1'b0}};
if (count_reg == 0) begin
state_next = STATE_IDLE;
end else begin
count_next = count_reg - 1;
state_next = STATE_DELETE;
end
end
endcase
end
always @(posedge clk) begin
if (rst) begin
state_reg <= STATE_INIT;
count_reg <= {SLICE_WIDTH{1'b1}};
write_busy_reg <= 1'b1;
end else begin
state_reg <= state_next;
count_reg <= count_next;
write_busy_reg <= state_next != STATE_IDLE;
end
write_addr_reg <= write_addr_next;
write_data_padded_reg <= write_data_padded_next;
end
endmodule
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