e100: squashed work on bus implementation on GPMC

1 files changed, 159 insertions, 0 deletions

diff --git a/usrp2/gpmc/fifo_to_gpmc.v b/usrp2/gpmc/fifo_to_gpmc.v
new file mode 100644
index 000000000..42c71d2d6
--- /dev/null
+++ b/usrp2/gpmc/fifo_to_gpmc.v
@@ -0,0 +1,159 @@
+//
+// 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/>.
+//
+
+////////////////////////////////////////////////////////////////////////
+// FIFO to GPMC
+//
+// Reads frames from FIFO interface and writes them into BRAM pages.
+// The GPMC is asynchronously alerted when a BRAM page has been filled.
+//
+// EM_CLK:
+// A GPMC read transaction consists of two EM_CLK cycles (idle low).
+//
+// EM_OE:
+// Output enable is actually the combination of ~NOE & ~NCS.
+// The output enable is only active for the second rising edge,
+// to ensure one edge per transaction to transition on.
+//
+// EM_D:
+// The BRAM performs a read on the first rising edge into EM_D.
+// Then, data will then be read on the next rising edge by GPMC.
+//
+// EM_A:
+// On the first rising edge of EM_CLK, the address is held.
+// On the second rising edge, the address is set for the next transaction.
+////////////////////////////////////////////////////////////////////////
+
+module fifo_to_gpmc
+  #(parameter PTR_WIDTH = 2, parameter ADDR_WIDTH = 10)
+  (input clk, input reset, input clear, input arst,
+   input [17:0] data_i, input src_rdy_i, output dst_rdy_o,
+   output [15:0] EM_D, input [ADDR_WIDTH:1] EM_A, input EM_CLK, input EM_OE,
+   output reg data_available);
+
+    //states for the GPMC side of things
+    wire [17:0] data_o;
+    reg gpmc_state;
+    reg [ADDR_WIDTH:1] addr;
+    reg [PTR_WIDTH:0] gpmc_ptr, next_gpmc_ptr;
+    localparam GPMC_STATE_START = 0;
+    localparam GPMC_STATE_EMPTY = 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_FILL = 1;
+
+    //------------------------------------------------------------------
+    // State machine to control the data from GPMC to BRAM
+    //------------------------------------------------------------------
+    always @(posedge EM_CLK or posedge arst) begin
+        if (arst) begin
+            gpmc_state <= GPMC_STATE_START;
+            gpmc_ptr <= 0;
+            next_gpmc_ptr <= 0;
+            addr <= 0;
+        end
+        else if (EM_OE) begin
+            addr <= EM_A + 1;
+            case(gpmc_state)
+
+            GPMC_STATE_START: begin
+                if (EM_A == 0) begin
+                    gpmc_state <= GPMC_STATE_EMPTY;
+                    next_gpmc_ptr <= gpmc_ptr + 1;
+                end
+            end
+
+            GPMC_STATE_EMPTY: begin
+                if (EM_A == 10'h3ff) begin
+                    gpmc_state <= GPMC_STATE_START;
+                    gpmc_ptr <= next_gpmc_ptr;
+                end
+            end
+
+            endcase //gpmc_state
+        end //EM_WE
+    end //always
+
+    //------------------------------------------------------------------
+    // High when the gpmc pointer has not caught up to the fifo pointer.
+    //------------------------------------------------------------------
+    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_fill = (fifo_ptr ^ (1 << PTR_WIDTH)) != safe_gpmc_ptr;
+
+    //------------------------------------------------------------------
+    // Glich free generation of data available signal:
+    // Data is available when the pointers dont match.
+    //------------------------------------------------------------------
+    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) data_available <= 0;
+        else               data_available <= safe_next_gpmc_ptr != fifo_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_fill) fifo_state <= FIFO_STATE_FILL;
+                counter <= 0;
+            end
+
+            FIFO_STATE_FILL: begin
+                if (src_rdy_i && dst_rdy_o && data_i[17]) begin
+                    fifo_state <= FIFO_STATE_CLAIM;
+                    fifo_ptr <= fifo_ptr + 1;
+                end
+                if (src_rdy_i && dst_rdy_o) begin
+                    counter <= counter + 1;
+                end
+            end
+
+            endcase //fifo_state
+        end
+    end //always
+
+    assign dst_rdy_o = fifo_state == FIFO_STATE_FILL;
+
+    //assign data from bram output
+    assign EM_D = data_o[15:0];
+
+    //instantiate dual ported bram for async read + write
+    ram_2port #(.DWIDTH(18),.AWIDTH(PTR_WIDTH + ADDR_WIDTH)) async_fifo_bram
+     (.clka(clk),.ena(1'b1),.wea(src_rdy_i && dst_rdy_o),
+      .addra({fifo_ptr[PTR_WIDTH-1:0], counter}),.dia(data_i),.doa(),
+      .clkb(EM_CLK),.enb(1'b1),.web(1'b0),
+      .addrb({gpmc_ptr[PTR_WIDTH-1:0], addr}),.dib(18'h3ffff),.dob(data_o));
+
+endmodule // fifo_to_gpmc