HyperRAM in simulation

- Simulation model of HyperRAM device, based on W956D8MBYA.
- Uses a dual-port RAM for the memory itself, with one port being
  used for data reads and the other for data writes.
- Implement simple models of FPGA primitives for use in simulation.

Author: alees24

dv/models/fpga/rtl/IOBUF.v

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+// Copyright lowRISC contributors.
+// Licensed under the Apache License, Version 2.0, see LICENSE for details.
+// SPDX-License-Identifier: Apache-2.0
+
+// This is a crude model of the Xilinx IOBUF primitive; enough to make the
+// OpenHBMC implementation simulate correctly.
+module IOBUF #(
+  parameter DRIVE = 0,
+  parameter SLEW  = "SLOW"
+) (
+  output O,
+  inout  IO,
+  input  I,
+  input  T
+);
+
+assign O = IO;
+assign IO = T ? 1'bZ : I;
+
+endmodule
+

dv/models/fpga/rtl/ISERDESE2.v

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+// Copyright lowRISC contributors.
+// Licensed under the Apache License, Version 2.0, see LICENSE for details.
+// SPDX-License-Identifier: Apache-2.0
+
+// This is a crude model of the Xilinx ISERDESE2 primitive; enough to make the
+// OpenHBMC implementation simulate correctly.
+module ISERDESE2 #(
+  parameter SERDES_MODE       = "MASTER",
+  parameter INTERFACE_TYPE    = "NETWORKING",
+  parameter DATA_RATE         = "DDR",
+  parameter DATA_WIDTH        = 6,
+  parameter DYN_CLKDIV_INV_EN = "FALSE",
+  parameter DYN_CLK_INV_EN    = "FALSE",
+  parameter OFB_USED          = "NONE",
+  parameter IOBDELAY          = 0,
+  parameter NUM_CE            = 1,
+  parameter INIT_Q1           = 1'b0,
+  parameter INIT_Q2           = 1'b0,
+  parameter INIT_Q3           = 1'b0,
+  parameter INIT_Q4           = 1'b0,
+  parameter SRVAL_Q1          = 1'b0,
+  parameter SRVAL_Q2          = 1'b0,
+  parameter SRVAL_Q3          = 1'b0,
+  parameter SRVAL_Q4          = 1'b0
+) (
+  output  O,
+
+  output  Q1,
+  output  Q2,
+  output  Q3,
+  output  Q4,
+  output  Q5,
+  output  Q6,
+  output  Q7,
+  output  Q8,
+
+  input   BITSLIP,
+
+  input   CE1,
+  input   CE2,
+
+  input   CLK,
+  input   CLKB,
+
+  input   CLKDIV,
+  input   CLKDIVP,
+  input   OCLK,
+  input   OCLKB,
+
+  input   D,
+  input   DDLY,
+
+  input   OFB,
+  input   RST,
+
+  input   DYNCLKDIVSEL,
+  input   DYNCLKSEL,
+
+  output  SHIFTOUT1,
+  output  SHIFTOUT2,
+
+  input   SHIFTIN1,
+  input   SHIFTIN2
+);
+
+  reg [8:1] iserdes_int;
+  always @(edge CLK or posedge RST) begin
+    if (RST) begin
+      iserdes_int <= {2{SRVAL_Q4, SRVAL_Q3, SRVAL_Q2, SRVAL_Q1}};
+    end else begin
+      iserdes_int <= {iserdes_int[7:1], D};
+    end
+  end
+
+  // In the ISERDESE2 module, Q8 is the oldest bit received.
+  assign {Q8,Q7,Q6,Q5,Q4,Q3,Q2,Q1} = iserdes_int;
+  assign O = D;
+
+  // These outputs are unused.
+  assign {SHIFTOUT2, SHIFTOUT1} = 2'b0;
+
+endmodule
+

dv/models/fpga/rtl/OBUF.v

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+// Copyright lowRISC contributors.
+// Licensed under the Apache License, Version 2.0, see LICENSE for details.
+// SPDX-License-Identifier: Apache-2.0
+
+// This is a crude model of the Xilinx OBUF primitive; enough to make the
+// OpenHBMC implementation simulate correctly.
+module OBUF #(
+  parameter DRIVE = 0,
+  parameter SLEW  = "SLOW"
+) (
+  input  I,
+  output O
+);
+
+assign O = I;
+
+endmodule
+

dv/models/fpga/rtl/ODDR.v

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+// Copyright lowRISC contributors.
+// Licensed under the Apache License, Version 2.0, see LICENSE for details.
+// SPDX-License-Identifier: Apache-2.0
+
+// This is a crude model of the Xilinx ODDR primitive; enough to make the
+// OpenHBMC implementation simulate correctly.
+module ODDR #(
+  parameter DDR_CLK_EDGE = "SAME_EDGE",
+  parameter INIT         = 1'b0,
+  parameter SRTYPE       = "ASYNC"
+) (
+  output Q,   // DDR output.
+  input  C,   // Clock input.
+  input  CE,  // Clock Enable.
+  input  D1,  // Two data inputs.
+  input  D2,
+  input  R,   // ReSet inputs.
+  input  S
+);
+
+  // Phase detection; PH is asserted during the second (negative edge)
+  // phase of the clock 'C.'
+  //         ___     ___
+  // C   ___/   \___/   \___
+  // PH   1   0   1   0   1
+
+  reg PH, PC, NC;
+  always @(posedge C) PC <= !PC;
+  always @(negedge C) NC <= !NC;
+  assign PH = !(PC ^ NC);
+
+  reg S2;
+  if (DDR_CLK_EDGE == "SAME_EDGE") begin : gen_same_edge
+    // Both data inputs are presented together on posedge.
+    always @(posedge C) begin
+      if (CE) S2 <= D2;
+    end
+  end else begin : gen_opposite_edge
+    // Inputs are presented on opposite edges.
+    assign S2 = D2;
+  end
+
+  // Output is clocked on both edges of clock input 'C'.
+  reg OUT;
+  always @(edge C, posedge R, posedge S) begin
+    if (R || S) OUT <= S & ~R;
+    else if (CE) OUT <= PH ? D1 : S2;
+  end
+  assign Q = OUT;
+
+endmodule
+