diff options
Diffstat (limited to 'fpga/usrp2/gpmc/gpmc_to_fifo.v')
| -rw-r--r-- | fpga/usrp2/gpmc/gpmc_to_fifo.v | 157 |
1 files changed, 157 insertions, 0 deletions
diff --git a/fpga/usrp2/gpmc/gpmc_to_fifo.v b/fpga/usrp2/gpmc/gpmc_to_fifo.v new file mode 100644 index 000000000..4aa55953a --- /dev/null +++ b/fpga/usrp2/gpmc/gpmc_to_fifo.v @@ -0,0 +1,157 @@ +// +// Copyright 2011 Ettus Research LLC +// +// This program is free software: you can redistribute it and/or modify +// it under the terms of the GNU General Public License as published by +// the Free Software Foundation, either version 3 of the License, or +// (at your option) any later version. +// +// This program is distributed in the hope that it will be useful, +// but WITHOUT ANY WARRANTY; without even the implied warranty of +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +// GNU General Public License for more details. +// +// You should have received a copy of the GNU General Public License +// along with this program. If not, see <http://www.gnu.org/licenses/>. +// + +//////////////////////////////////////////////////////////////////////// +// GPMC to FIFO +// +// Reads frames from BRAM pages and writes them into FIFO interface. +// The GPMC is asynchronously alerted when a BRAM page is available. +// +// EM_CLK: +// A GPMC read transaction consists of one EM_CLK cycle (idle low). +// +// EM_WE: +// Write enable is actually the combination of ~NWE & ~NCS. +// The write enable is active for the entire transaction. +// +// EM_D: +// Data is set on the rising edge and written into BRAM on the falling edge. +// +// EM_A: +// Address is set on the rising edge and read by BRAM on the falling edge. +//////////////////////////////////////////////////////////////////////// + +module gpmc_to_fifo + #(parameter PTR_WIDTH = 2, parameter ADDR_WIDTH = 10) + (input [15:0] EM_D, input [ADDR_WIDTH:1] EM_A, input EM_CLK, input EM_WE, + input clk, input reset, input clear, input arst, + output [17:0] data_o, output src_rdy_o, input dst_rdy_i, + output reg have_space); + + //states for the GPMC side of things + wire [17:0] data_i; + reg gpmc_state; + reg [ADDR_WIDTH:1] last_addr; + reg [PTR_WIDTH:0] gpmc_ptr, next_gpmc_ptr; + localparam GPMC_STATE_START = 0; + localparam GPMC_STATE_FILL = 1; + + //states for the FIFO side of things + reg fifo_state; + reg [ADDR_WIDTH-1:0] counter; + reg [PTR_WIDTH:0] fifo_ptr; + localparam FIFO_STATE_CLAIM = 0; + localparam FIFO_STATE_EMPTY = 1; + + //------------------------------------------------------------------ + // State machine to control the data from GPMC to BRAM + //------------------------------------------------------------------ + always @(negedge EM_CLK or posedge arst) begin + if (arst) begin + gpmc_state <= GPMC_STATE_START; + gpmc_ptr <= 0; + next_gpmc_ptr <= 0; + end + else if (EM_WE) begin + case(gpmc_state) + + GPMC_STATE_START: begin + if (EM_A == 0) begin + gpmc_state <= GPMC_STATE_FILL; + last_addr <= {EM_D[ADDR_WIDTH-2:0], 1'b0} - 1'b1; + next_gpmc_ptr <= gpmc_ptr + 1; + end + end + + GPMC_STATE_FILL: begin + if (data_i[17]) begin + gpmc_state <= GPMC_STATE_START; + gpmc_ptr <= next_gpmc_ptr; + end + end + + endcase //gpmc_state + end //EM_WE + end //always + + //------------------------------------------------------------------ + // A block ram is available to empty when the pointers dont match. + //------------------------------------------------------------------ + wire [PTR_WIDTH:0] safe_gpmc_ptr; + cross_clock_reader #(.WIDTH(PTR_WIDTH+1)) read_gpmc_ptr + (.clk(clk), .rst(reset | clear), .in(gpmc_ptr), .out(safe_gpmc_ptr)); + + wire bram_available_to_empty = safe_gpmc_ptr != fifo_ptr; + + //------------------------------------------------------------------ + // Glich free generation of have space signal: + // High when the fifo pointer has not caught up to the gpmc pointer. + //------------------------------------------------------------------ + wire [PTR_WIDTH:0] safe_next_gpmc_ptr; + cross_clock_reader #(.WIDTH(PTR_WIDTH+1)) read_next_gpmc_ptr + (.clk(clk), .rst(reset | clear), .in(next_gpmc_ptr), .out(safe_next_gpmc_ptr)); + + always @(posedge clk) + if (reset | clear) have_space <= 0; + else have_space <= (fifo_ptr ^ (1 << PTR_WIDTH)) != safe_next_gpmc_ptr; + + //------------------------------------------------------------------ + // State machine to control the data from BRAM to FIFO + //------------------------------------------------------------------ + always @(posedge clk) begin + if (reset | clear) begin + fifo_state <= FIFO_STATE_CLAIM; + fifo_ptr <= 0; + counter <= 0; + end + else begin + case(fifo_state) + + FIFO_STATE_CLAIM: begin + if (bram_available_to_empty) fifo_state <= FIFO_STATE_EMPTY; + counter <= 0; + end + + FIFO_STATE_EMPTY: begin + if (src_rdy_o && dst_rdy_i && data_o[17]) begin + fifo_state <= FIFO_STATE_CLAIM; + fifo_ptr <= fifo_ptr + 1; + end + if (src_rdy_o && dst_rdy_i) begin + counter <= counter + 1; + end + end + + endcase //fifo_state + end + end //always + + assign src_rdy_o = fifo_state == FIFO_STATE_EMPTY; + + //assign data and frame bits to bram input + assign data_i[15:0] = EM_D; + assign data_i[16] = (gpmc_state == GPMC_STATE_START); + assign data_i[17] = (EM_A == last_addr); + + //instantiate dual ported bram for async read + write + ram_2port #(.DWIDTH(18),.AWIDTH(PTR_WIDTH + ADDR_WIDTH)) async_fifo_bram + (.clka(~EM_CLK),.ena(1'b1),.wea(EM_WE), + .addra({gpmc_ptr[PTR_WIDTH-1:0], EM_A}),.dia(data_i),.doa(), + .clkb(~clk),.enb(1'b1),.web(1'b0), + .addrb({fifo_ptr[PTR_WIDTH-1:0], counter}),.dib(18'h3ffff),.dob(data_o)); + +endmodule // gpmc_to_fifo |