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+INSTRUCTIONS
+================================
+
+# Building the B2xx FX3 Firmware
+
+The USRP B200 and B210 each use the Cypress FX3 USB3 PHY for USB3 connectivity.
+This device has an ARM core on it, which is programmed in C. This README will
+show you how to build our firmware source
+
+**A brief "Theory of Operations":**
+The host sends commands to the FX3, our USB3 PHY, which has an on-board ARM
+which runs the FX3 firmware code (hex file). That code translates commands into
+SPI commands to/from the AD9361. The SPI lines run through the FPGA (bin or bit
+file), where they are level-translated, and then head to the AD9361. Note that
+the FPGA takes no action on these SPI lines. They are passive pass-throughs.
+
+## Setting up the Cypress SDK
+
+In order to compile the USRP B200 and B210 firmware, you will need the FX3 SDK
+distributed by the FX3 manufacturer, Cypress Semiconductor. You can download the
+[FX3 SDK from here](http://www.cypress.com/?rID=57990).
+
+Once you have downloaded it, extract the ARM cross-compiler sub-directory from
+the zip file and put it somewhere useful. The highest level directory you need
+is `arm-2011.03/`.
+
+Now that you have extracted the cross compilation toolchain, you need to set up
+some environment variables to tell the B2xx `makefile` where to look for the
+tools. These variables are:
+
+```
+    $ export ARMGCC_INSTALL_PATH=<your path>/arm-2011.03
+    $ export ARMGCC_VERSION=4.5.2
+```
+
+Now, you'll need to set-up the Cypress SDK, as well. In the SDK, navigate to
+the `firmware` directory, and copy the following sub-directories into
+`uhd.git/firmware/fx3`: `common/`, `lpp_source/`, `u3p_firmware/`.
+
+Your directory structure should now look like:
+
+```
+uhd.git/
+       |
+       --firmware/
+                 |
+                 --fx3/
+                      |
+                      --ad9361/             # From UHD
+                      --b200/               # From UHD
+                      --common/             # From Cypress SDK
+                      --gpif2_designer/     # From UHD
+                      --lpp_source/         # From Cypress SDK
+                      --u3p_firmware/       # From Cypress SDK
+                      --README.md           # From UHD
+```
+
+
+## Applying the Patch to the Toolchain
+
+Now, you'll need to apply a patch to a couple of files in the Cypress SDK. Head
+into the `common/` directory you just copied from the Cypress SDK, and apply the
+patch `b200/fx3_mem_map.patch`.
+
+```
+    # cd uhd.git/firmware/common/
+    $ patch -p2 < ../b200/fx3_mem_map.patch
+```
+
+If you don't see any errors print on the screen, then the patch was successful.
+
+## Building the Firmware
+
+Now, you should be able to head into the `b200/` directory and simply build the
+firmware:
+
+```
+    $ cd uhd.git/firmware/fx3/b200
+    $ make
+```
+
+It will generate a `usrp_b200_fw.hex` file, which you can then give to UHD to
+program your USRP B200 or USRP B210.
+