Merge FPGA repository back into UHD repository

The FPGA codebase was removed from the UHD repository in 2014 to reduce
the size of the repository. However, over the last half-decade, the
split between the repositories has proven more burdensome than it has
been helpful. By merging the FPGA code back, it will be possible to
create atomic commits that touch both FPGA and UHD codebases. Continuous
integration testing is also simplified by merging the repositories,
because it was previously difficult to automatically derive the correct
UHD branch when testing a feature branch on the FPGA repository.

This commit also updates the license files and paths therein.

We are therefore merging the repositories again. Future development for
FPGA code will happen in the same repository as the UHD host code and
MPM code.

== Original Codebase and Rebasing ==

The original FPGA repository will be hosted for the foreseeable future
at its original local location: https://github.com/EttusResearch/fpga/

It can be used for bisecting, reference, and a more detailed history.

The final commit from said repository to be merged here is
05003794e2da61cabf64dd278c45685a7abad7ec. This commit is tagged as
v4.0.0.0-pre-uhd-merge.

If you have changes in the FPGA repository that you want to rebase onto
the UHD repository, simply run the following commands:

- Create a directory to store patches (this should be an empty
  directory):

    mkdir ~/patches

- Now make sure that your FPGA codebase is based on the same state as
  the code that was merged:

    cd src/fpga # Or wherever your FPGA code is stored
    git rebase v4.0.0.0-pre-uhd-merge

  Note: The rebase command may look slightly different depending on what
  exactly you're trying to rebase.

- Create a patch set for your changes versus v4.0.0.0-pre-uhd-merge:

    git format-patch v4.0.0.0-pre-uhd-merge -o ~/patches

  Note: Make sure that only patches are stored in your output directory.
  It should otherwise be empty. Make sure that you picked the correct
  range of commits, and only commits you wanted to rebase were exported
  as patch files.

- Go to the UHD repository and apply the patches:

    cd src/uhd # Or wherever your UHD repository is stored
    git am --directory fpga ~/patches/*
    rm -rf ~/patches # This is for cleanup

== Contributors ==

The following people have contributed mainly to these files (this list
is not complete):

Co-authored-by: Alex Williams <alex.williams@ni.com>
Co-authored-by: Andrej Rode <andrej.rode@ettus.com>
Co-authored-by: Ashish Chaudhari <ashish@ettus.com>
Co-authored-by: Ben Hilburn <ben.hilburn@ettus.com>
Co-authored-by: Ciro Nishiguchi <ciro.nishiguchi@ni.com>
Co-authored-by: Daniel Jepson <daniel.jepson@ni.com>
Co-authored-by: Derek Kozel <derek.kozel@ettus.com>
Co-authored-by: EJ Kreinar <ej@he360.com>
Co-authored-by: Humberto Jimenez <humberto.jimenez@ni.com>
Co-authored-by: Ian Buckley <ian.buckley@gmail.com>
Co-authored-by: Jörg Hofrichter <joerg.hofrichter@ni.com>
Co-authored-by: Jon Kiser <jon.kiser@ni.com>
Co-authored-by: Josh Blum <josh@joshknows.com>
Co-authored-by: Jonathon Pendlum <jonathan.pendlum@ettus.com>
Co-authored-by: Martin Braun <martin.braun@ettus.com>
Co-authored-by: Matt Ettus <matt@ettus.com>
Co-authored-by: Michael West <michael.west@ettus.com>
Co-authored-by: Moritz Fischer <moritz.fischer@ettus.com>
Co-authored-by: Nick Foster <nick@ettus.com>
Co-authored-by: Nicolas Cuervo <nicolas.cuervo@ettus.com>
Co-authored-by: Paul Butler <paul.butler@ni.com>
Co-authored-by: Paul David <paul.david@ettus.com>
Co-authored-by: Ryan Marlow <ryan.marlow@ettus.com>
Co-authored-by: Sugandha Gupta <sugandha.gupta@ettus.com>
Co-authored-by: Sylvain Munaut <tnt@246tNt.com>
Co-authored-by: Trung Tran <trung.tran@ettus.com>
Co-authored-by: Vidush Vishwanath <vidush.vishwanath@ettus.com>
Co-authored-by: Wade Fife <wade.fife@ettus.com>


Original-commit: bafa9d95453387814ef25e6b6256ba8db2df612f

lib/rfnoc/axi_round_and_clip.v

@@ -0,0 +1,69 @@
+//
+// Copyright 2014, Ettus Research
+// Copyright 2018 Ettus Research, a National Instruments Company
+//
+// SPDX-License-Identifier: LGPL-3.0-or-later
+//
+//
+// Reduce the bitwidth of an input stream. This module will both round
+// and clip, meaning that the lower bits will be removed by rounding to
+// the nearest value, and the top bits will be snipped (but without
+// causing numerical overflows).
+//
+// Example: If WIDTH_IN==24, WIDTH_OUT==16, and CLIP_BITS==3, the output
+// Will remove the top 3 bits (by clipping), and remove the bottom 5
+// bits by rounding, leaving 24 - 3 - 5 == 16 bits.
+//
+// Note that this module has two stages (round, then clip) which will
+// both have a FIFO of length FIFOSIZE. However, when a stage is not
+// required it will have *no* FIFO, but instead just pass through the
+// data. In the extreme case where WIDTH_IN==WIDTH_OUT and CLIP_BITS==0,
+// there are no FIFOs and this module becomes an AXI stream passthrough.
+module axi_round_and_clip
+#(
+  parameter WIDTH_IN=24,
+  parameter WIDTH_OUT=16,
+  parameter CLIP_BITS=3,
+  parameter FIFOSIZE=1)  // FIFOSIZE = 1, single output register
+(
+  input clk, input reset,
+  input [WIDTH_IN-1:0] i_tdata, input i_tlast, input i_tvalid, output i_tready,
+  output [WIDTH_OUT-1:0] o_tdata, output o_tlast, output o_tvalid, input o_tready
+);
+
+  wire [WIDTH_OUT+CLIP_BITS-1:0] int_tdata;
+  wire int_tlast, int_tvalid, int_tready;
+
+  generate
+    if (WIDTH_IN == WIDTH_OUT+CLIP_BITS) begin
+       assign int_tdata    = i_tdata;
+       assign int_tlast    = i_tlast;
+       assign int_tvalid   = i_tvalid;
+       assign i_tready     = int_tready;
+    end else begin
+      axi_round #(
+        .WIDTH_IN(WIDTH_IN), .WIDTH_OUT(WIDTH_OUT+CLIP_BITS),
+        .round_to_nearest(1), .FIFOSIZE(FIFOSIZE))
+      axi_round (
+        .clk(clk), .reset(reset),
+        .i_tdata(i_tdata), .i_tlast(i_tlast), .i_tvalid(i_tvalid), .i_tready(i_tready),
+        .o_tdata(int_tdata), .o_tlast(int_tlast), .o_tvalid(int_tvalid), .o_tready(int_tready));
+    end
+
+    if (CLIP_BITS == 0) begin
+      assign o_tdata    = int_tdata;
+      assign o_tlast    = int_tlast;
+      assign o_tvalid   = int_tvalid;
+      assign int_tready = o_tready;
+    end else begin
+      axi_clip #(
+        .WIDTH_IN(WIDTH_OUT+CLIP_BITS), .WIDTH_OUT(WIDTH_OUT),
+        .FIFOSIZE(FIFOSIZE))
+      axi_clip (
+        .clk(clk), .reset(reset),
+        .i_tdata(int_tdata), .i_tlast(int_tlast), .i_tvalid(int_tvalid), .i_tready(int_tready),
+        .o_tdata(o_tdata), .o_tlast(o_tlast), .o_tvalid(o_tvalid), .o_tready(o_tready));
+    end
+  endgenerate
+
+endmodule // round_and_clip