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//
// Copyright 2013 Ettus Research LLC
//
//
// This module implements a highly customized TCAM that enbales forwarding
// decisions to be made on a 16bit field from a VITA SID field.
// The 16bits are allocated by convention as 8 bits of Network address
// (Addresses USRP's etc) and 8 bits of Host address (adresses endpoints in
// a USRP). By definition if the DEST field in the SID addresses a different
// USRP than this one then we don't care about the Host field, only the Network Field.
// We only look at the Host Field when the Network field addresses us.
// Thus Need TCAM of 256+256 entries with Log2(N) bits, where N is the number of
// slave(output) ports on the crossbar switch.
//
//
//
// SID format:
//
// |--------|---------|--------|---------|
// | SOURCE | DEST | DEST |
// | ADDRESS | NETWORK| HOST |
// |--------|---------|--------|---------|
// 8 8 8 8
//
`define LOG2(N) (\
N < 2 ? 0 : \
N < 4 ? 1 : \
N < 8 ? 2 : \
N < 16 ? 3 : \
N < 32 ? 4 : \
N < 64 ? 5 : \
N < 128 ? 6 : \
N < 256 ? 7 : \
N < 512 ? 8 : \
N < 1024 ? 9 : \
10)
module axi_forwarding_cam
#(
parameter BASE = 0, // BASE address for setting registers in this block. (512 addrs used)
parameter WIDTH=64, // Bit width of FIFO word.
parameter NUM_OUTPUTS=2 // Number of outputs (destinations) in crossbar.
)
(
input clk,
input reset,
input clear,
// Monitored FIFO signals
input [WIDTH-1:0] o_tdata,
input o_tvalid,
input o_tready,
input o_tlast,
input pkt_present,
// Configuration
input [7:0] local_addr,
// Setting Bus
input set_stb,
input [15:0] set_addr,
input [31:0] set_data,
// Forwarding Flags
output reg [NUM_OUTPUTS-1:0] forward_valid,
input [NUM_OUTPUTS-1:0] forward_ack,
// readback bus
input rb_rd_stb,
input [`LOG2(NUM_OUTPUTS)-1:0] rb_addr,
output [31:0] rb_data
);
localparam WAIT_SOF = 0;
localparam WAIT_EOF = 1;
reg state;
localparam IDLE = 0;
localparam FORWARD = 1;
localparam WAIT = 2;
reg [1:0] demux_state;
reg [15:0] dst;
reg dst_valid, dst_valid_reg;
wire local_dst;
wire [8:0] read_addr;
//
// Monitor packets leaving FIFO
//
always @(posedge clk)
if (reset | clear) begin
state <= WAIT_SOF;
end else
case(state)
//
// After RESET or the EOF of previous packet, the first cycle with
// output valid asserted is the SOF and presents the Header word.
// The cycle following the concurrent presentation of asserted output
// valid and output ready presents the word following the header.
//
WAIT_SOF:
if (o_tvalid && o_tready) begin
state <= WAIT_EOF;
end else begin
state <= WAIT_SOF;
end
//
// EOF is signalled by o_tlast asserted whilst output valid and ready asserted.
//
WAIT_EOF:
if (o_tlast && o_tvalid && o_tready) begin
state <= WAIT_SOF;
end else begin
state <= WAIT_EOF;
end
endcase // case(in_state)
//
// Extract Destination fields(s) from SID
//
always @(posedge clk)
if (reset | clear) begin
dst <= 0;
dst_valid <= 0;
dst_valid_reg <= 0;
end else if (o_tvalid && (state == WAIT_SOF) && pkt_present) begin
// SID will remain valid until o_tready is asserted as this will cause a state transition.
dst <= o_tdata[15:0];
dst_valid <= 1;
dst_valid_reg <= dst_valid;
end else begin
dst_valid <= 0;
dst_valid_reg <= dst_valid;
end
//
// Is Network field in DST our local address?
//
assign local_dst = (dst[15:8] == local_addr) && dst_valid;
//
// Mux address to RAM so that it searches CAM for Network field or Host field.
// Network addresses are stored in the lower 256 locations, host addresses the upper 256.
//
assign read_addr = {local_dst,(local_dst ? dst[7:0] : dst[15:8])};
//
// Imply a block RAM here, 512xCeil(Log2(NUM_OUTPUTS))
//
//synthesis attribute ram_style of mem is block
reg [(`LOG2(NUM_OUTPUTS))-1 : 0] mem [0:511];
reg [8:0] read_addr_reg;
wire write;
wire [`LOG2(NUM_OUTPUTS)-1:0] read_data;
assign write = (set_addr[15:9] == (BASE >>9)) && set_stb; // Addr decode.
always @(posedge clk)
begin
read_addr_reg <= read_addr;
if (write) begin
mem[set_addr[8:0]] <= set_data[`LOG2(NUM_OUTPUTS)-1:0];
end
end
assign read_data = mem[read_addr_reg];
//
// State machine to manage forwarding flags.
//
always @(posedge clk)
if (reset | clear) begin
demux_state <= IDLE;
end else
case(demux_state)
// Wait for Valid DST which indicates a new packet lookup in the CAM.
IDLE: begin
if (dst_valid_reg == 1) begin
forward_valid <= 1 << read_data;
demux_state <= FORWARD;
end
end
// When Slave/Output thats forwarding ACK's the forward flag, clear request and wait for packet to be transfered
FORWARD: begin
if ((forward_ack & forward_valid) != 0) begin
forward_valid <= 0;
demux_state <= WAIT;
end
end
// When packet transfered go back to idle.
WAIT: begin
if (forward_ack == 0)
demux_state <= IDLE;
end
endcase // case (demux_state)
//
// Compile forwarding statistics
// (This uses a lot of registers!)
//
genvar m;
reg [31:0] statistics [0:NUM_OUTPUTS-1];
generate
for (m = 0; m < NUM_OUTPUTS; m = m + 1) begin: generate_stats
always @(posedge clk)
if (reset | clear)
statistics[m] <= 0;
else if ((rb_addr == m) && rb_rd_stb)
statistics[m] <= 0;
else if (forward_ack[m] & forward_valid[m])
statistics[m] <= statistics[m] + 1;
end
endgenerate
assign rb_data = statistics[rb_addr];
endmodule
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