Many engineers, however, use MATLAB ® and Simulink ® to help with VHDL or Verilog test bench creation because the software provides productive and compact notation to describe algorithms, as well as visualization. One thing this example points out is that all VHDL structural models capable of simulation are described behaviorally. In a conventional VHDL ® or Verilog ® test bench, HDL code is used to describe the stimulus to a logic design and to check whether the design’s outputs match the specification. The first 6 times match your specification.Ī waveform display shows the counts, toggles, zero (representing the flip flop reset) and clock: When run the clock_gen_tb testbench reports clock events and shows that it meets your note): clock = note): clock = note): clock = note): clock = note): clock = note): clock = note): clock = note): clock = note): clock = note): clock = note): clock = note): clock = '1' The size of the counter and the number of events can be scaled up. Because you didn't specify any further edge events it's tailored to the size needed for the number of edge events you did specify. The counter wraps, which is easy to cure (it could stop instead for instance). The look up table used to determine the count values where a toggle occurs could be replaced with and/ors, etc. Report 'clock = ' & std_logic'image(clock) Signal cnt: unsigned (count'range) := (others => '0') - start at zeroĬonstant period: integer := 31 - 32 is the period of the the sequence Well we'd adjust the count comparison values down by one to compensate for the D Flip Flop and it would look something like this structurally: library ieee Ĭount: out std_logic_vector (4 downto 0)

The size of count is determined last even in 5 ns increments. The toggle signal is an enable for a D Flip Flop (clock is the output) with it's Qnot connected to D run off the high speed clock (supplied externally from a testbench). If the clock is continuous you pick a count to restore the count to all '0's. at count = 5 (25 ns), 7 (35 ns), 10 (50 ns) a combinatorial signal toggle goes true ('1'). Imagine a counter that counts 5 ns period clocks and an initial value for clock of '0' and the counter of (others => '0').

Testbench generator vhdl