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>

1 files changed, 49 insertions, 0 deletions

diff --git a/fpga/docs/usrp2/customize_signal_chain.md b/fpga/docs/usrp2/customize_signal_chain.md
new file mode 100644
index 000000000..dfd28b3cc
--- /dev/null
+++ b/fpga/docs/usrp2/customize_signal_chain.md
@@ -0,0 +1,49 @@
+# Customizing the Signal Chain in Generation 2 products
+
+## Adding DSP logic to Generation 2 products
+
+As part of the USRP FPGA build-framework, there are several convenient places
+for users to insert custom DSP modules into the transmit and receive chains.
+
+- Before the DDC module
+- After the DDC module
+- Replace the DDC module
+- Before the DUC module
+- After the DUC module
+- Replace the DUC module
+- As an RX packet engine
+- As an TX packet engine
+
+### Customizing the top level makefile
+
+Each USRP device has a makefile associated with it. This makefile contains all
+of the necessary build rules. When making a customized FPGA design, start by
+copying the current makefile for your device. Makefiles can be found in
+`usrp2/top/{product}/Makefile`
+
+Edit your new makefile:
+- Set BUILD_DIR to a unique directory name
+- Set CUSTOM_SRCS for your verilog sources
+- Set CUSTOM_DEFS (see section below)
+
+### Inserting custom modules
+
+CUSTOM_DEFS is a string of space-separate key-value pairs. Set the CUSTOM_DEFS
+variable so the FPGA fabric glue will substitute your custom modules into the
+DSP chain.
+
+Example:
+
+    CUSTOM_DEFS = "TX_ENG0_MODULE=my_tx_engine RX_ENG0_MODULE=my_rx_engine"
+
+Where `my_tx_engine` and `my_rx_engine` are the names of custom verilog modules.
+
+The following module definition keys are possible (X is a DSP number):
+
+- `TX_ENG<X>_MODULE`: Set the module for the transmit chain engine.
+- `RX_ENG<X>_MODULE`: Set the module for the receive chain engine.
+- `RX_DSP<X>_MODULE`: Set the module for the transmit dsp chain.
+- `TX_DSP<X>_MODULE`: Set the module for the receive dsp chain.
+
+Examples of custom modules can be found in the Verilog files in `usrp2/custom/`.
+