fpga: x400: Add support for X410 motherboard FPGA

Co-authored-by: Andrew Moch <Andrew.Moch@ni.com>
Co-authored-by: Daniel Jepson <daniel.jepson@ni.com>
Co-authored-by: Javier Valenzuela <javier.valenzuela@ni.com>
Co-authored-by: Joerg Hofrichter <joerg.hofrichter@ni.com>
Co-authored-by: Kumaran Subramoniam <kumaran.subramoniam@ni.com>
Co-authored-by: Max Köhler <max.koehler@ni.com>
Co-authored-by: Michael Auchter <michael.auchter@ni.com>
Co-authored-by: Paul Butler <paul.butler@ni.com>
Co-authored-by: Wade Fife <wade.fife@ettus.com>
Co-authored-by: Hector Rubio <hrubio@ni.com>

1 files changed, 87 insertions, 0 deletions

diff --git a/fpga/usrp3/top/x400/rf/100m/duc_saturate.vhd b/fpga/usrp3/top/x400/rf/100m/duc_saturate.vhd
new file mode 100644
index 000000000..5cb1bc1fc
--- /dev/null
+++ b/fpga/usrp3/top/x400/rf/100m/duc_saturate.vhd
@@ -0,0 +1,87 @@
+--
+-- Copyright 2021 Ettus Research, a National Instruments Brand
+--
+-- SPDX-License-Identifier: LGPL-3.0-or-later
+--
+-- Module: duc_saturate
+--
+-- Description:
+--
+--   Saturation logic for reducing 2x24 bit words to 2x16 bit words. See
+--   comments below for full description.
+--
+
+library IEEE;
+  use IEEE.std_logic_1164.all;
+  use IEEE.numeric_std.all;
+
+entity duc_saturate is
+  port(
+    Clk            : in  std_logic;
+    cDataIn        : in  std_logic_vector(47 downto 0);
+    cDataValidIn   : in  std_logic;
+    cReadyForInput : out std_logic;
+    cDataOut       : out std_logic_vector(31 downto 0);
+    cDataValidOut  : out std_logic := '0'
+  );
+end duc_saturate;
+
+architecture RTL of duc_saturate is
+
+  signal cDataOutI : std_logic_vector(15 downto 0) := (others => '0');
+  signal cDataOutQ : std_logic_vector(15 downto 0) := (others => '0');
+
+begin
+
+  -----------------------------------------------------------------------------
+  -- Saturation
+  --
+  -- The output of the Xilinx FIR Compiler has already been rounded on the LSB
+  -- side, but hasn't been saturated on the MSB side.
+  -- Coefficients = 18 bit, 1 integer bit (1.17)
+  -- Data In = 16 bits, 1 integer bit (1.15)
+  -- Xilinx FIR core rounds to output to 3.31. The filter coefficients has a
+  -- gain of 3 to compensate for the amplitude loss in interpolation, the
+  -- Xilinx FIR core rounds the output to 3.15.
+  -- Data Out = 18 bits, 3 integer bits (3.15), with 16 LSBs already rounded
+  -- off inside the FIR core.
+  -- We need to manually saturate the 3.15 number back to a 1.15 number
+  --
+  -- If 3 MSBs = 000, output <= input without MSB, e.g. positive number < 1
+  -- If 3 MSBs = 0x1/01x, output <= 0.111111111111111, e.g. positive number >= 1
+  -- If 3 MSBs = 1x0/10x, output <= 1.000000000000000, e.g. negative number < -1
+  -- If 3 MSBs = 111, output <= input without MSB, e.g. negative number >= -1
+  -----------------------------------------------------------------------------
+Saturation:
+  process(Clk)
+  begin
+    if rising_edge(Clk) then
+      -- Pipeline data valid to match the data
+      cDataValidOut <= cDataValidIn;
+
+      -- I, from cDataIn(17 downto 0)
+      if cDataIn(17) = '0' and cDataIn(16 downto 15) /= "00" then
+        cDataOutI <= "0111111111111111";
+      elsif cDataIn(17) = '1' and cDataIn(16) /=  cDataIn(15) then
+        cDataOutI <= "1000000000000000";
+      else
+        cDataOutI <= cDataIn(15 downto 0);
+      end if;
+
+      -- Q, from cDataIn(41 downto 24)
+      if cDataIn(41) = '0' and cDataIn(40 downto 39) /= "00" then
+        cDataOutQ <= "0111111111111111";
+      elsif cDataIn(41) = '1' and
+            (not (cDataIn(40 downto 39) = "11")) then
+        cDataOutQ <= "1000000000000000";
+      else
+        cDataOutQ <= cDataIn(39 downto 24);
+      end if;
+
+    end if;
+  end process Saturation;
+
+  cDataOut <= cDataOutQ & cDataOutI;
+  cReadyForInput <= '1';
+
+end RTL;