VHDL UART

Description

A VHDL UART for communicating over a serial link with an FPGA. This example implements a loopback so that data received by the FPGA will be returned down the serial link.

The default settings for the link are 115200 BAUD, 8 Data, 1 Stop, No parity.

Source files

The following source files can be found in the 'source' directory.

File	Type	Description
uart.vhd	VHDL	UART implementation
loopback.vhd	VHDL	Instance UART in loopback @ 115200 baud & 100MHz
top.vhd	VHDL	Instance loopback in FPGA top level wrapper
tb_uart.vhd	VHDL	Testbench for the UART component
uart_unit_tests.py	Python	ChipTools unit test suite for tb_uart.vhd
uart.ucf	UCF	Constraints for Spartan 6 LX9 Microboard (Avnet)
fpga_unit_tests.py	Python	Hardware unit tests for the LX9 Microboard

The uart.xml file in the top level directory is a project file to allow you to build and test this design using the ChipTools framework

Getting Started

The following instructions explain how to test and build the loopback example using the ChipTools framework. Simulation and hardware tests are included.

Run the Unit Tests

To run the unit tests invoke ChipTools in the top level directory:

$ chiptools

Load the project and run the tests:

$ load_project uart.xml
$ run_tests

The default simulator is set to Modelsim, to run the tests using a different simulator supply either 'isim', 'ghdl' or 'vivado' to the run_tests command.

The report file: report.html is saved in the simulation directory and contains the results of the simulation test suite.

Synthesise the Design

A constraints file is provided to allow the design to be built for the Spartan 6 LX9 Microboard. To initiate a build perform the following in the top level directory:

$ chiptools
$ load_project uart.xml
$ synthesise lib_uart.top

The synthesis flow is set to 'ise' as this is targeted at a Spartan6 FPGA.

Build outputs will be automatically archived and stored in the synthesis directory.

Run the Hardware Unit Tests

A set of unit tests have been written to test the UART loopback example after it has been programmed onto a Spartan 6 LX9 Microboard. The unit tests check different transfer sizes of random data using the default BAUD rate of 115200.

The tests require PySerial to allow Python to read and write to the serial port. Before running the tests the board should be programmed and connected to your PC and the serial port setting in the unit test should be edited to map to the serial port of the FPGA board.

Further reading

Original release post

http://www.bytebash.com/2011/10/rs232-uart-vhdl/

ChipTools repository

http://github.com/pabennett/chiptools

ChipTools documentation

http://chiptools.readthedocs.org/en/latest/index.html