Adding implementation details for the Arty.

docs/Simulation/FPGA-Prototyping.rst

@@ -69,6 +69,12 @@ Adding this config. fragment will enable and connect the JTAG, UART, SPI, and I2
 
 Future peripherals to be supported include the Arty's SPI Flash EEPROM.
 
+Brief Implementation Description for Less Complicated Designs (Such as Arty), and Guidance for Adding/Changing Xilinx Collateral
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Like the VCU118, the basis for the Arty design is the creation of a special test harness that connects the external IO (which exist as Xilinx IP blackboxes) to the Chipyard design.
+This is done with the ``ArtyTestHarness`` in the basic default Arty target. However, unlike the ``VCU118TestHarness``, the ``ArtyTestHarness`` uses no ``Overlay``s, and instead directly connects chip top IO to the ports of the external IO blackboxes, using functions such as ``IOBUF`` provided by ``fpga-shells``. Unlike the VCU118 and other more complicated test harnesses, the Arty's Vivado collateral is not generated by ``Overlay``s, but rather are a static collection of ``create_ip`` and ``set_properties`` statements located in the files within ``fpga/fpga-shells/xilinx/arty/tcl`` and ``fpga/fpga-shells/xilinx/arty/constraints``. If the user wishes to re-map FPGA package pins to different harness-level IO, this may be changed within ``fpga/fpga-shells/xilinx/arty/constraints/arty-master.xdc``. The addition of new Xilinx IP blocks may be done in ``fpga-shells/xilinx/arty/tcl/ip.tcl``, mapped to harness-level IOs in ``arty-master.xdc``, and wired through from the test harness to the chip top using ``HarnessBinder``s and ssIOBinder``s.
+
 Running a Design on VCU118
 --------------------------