can-lite-vhdl

A lightweight Controller Area Network (CAN) controller in VHDL

This code provides a simple FIFO interface to a CAN controller. It was developed for use in conjunction with a CANopen controller (see canopen-vhdl) on an FPGA with (or using) limited resources, hence the minimal interface and selected status flags. While it is typical to use this module with an asynchronous (dual clock) FIFO, it is not required. However, it may be difficult to achieve the appropriate CAN timing with some application clocks, and FIFOs help prevent data loss (overflow) if status bits are not continuously checked. The values for the generics are typical of many CAN controllers, with the following relationships:

• Baud Rate, in bps = (Clock frequency, in Hz) / 2 / BAUD_RATE_PRESCALAR / (TIME_SEGMENT_1 + TIME_SEGMENT_2 + 1)
• Sample Point, % of bit time = (TIME_SEGMENT_1 + 1) / (TIME_SEGMENT_1 + TIME_SEGMENT_2 + 1)

Example:

• 24MHz Clock, BAUD_RATE_PRESCALAR = 1, TIME_SEGMENT_1 = 8, TIME_SEGMENT_2 = 3
• Baud Rate: 24000000 / 2 / 1 / (8 + 3 + 1) = 1000000 = 1 Mbps
• Sample Point: (8 + 1) / (8 + 3 + 1) = 75%

src/CanBus_pkg.vhd defines some data types, functions, and standard CANopen constants, as well as procedures for use in testbenches.

src/CanLite.vhd contains the top-level VHDL module (CanLite), as well as the submodules it depends on.

test/CanLite_tb.vhd is a simple testbench that uses Xilinx asynchronous FIFOs and connects two nodes on a virtual CAN bus.

Please excuse the mixed coding styles, as this code was adapted multiple times (see src/CanLite.vhd). The top-level file uses the coding style of GRC-PLC-CDD, which is an internal NASA document.