This design pattern shows a MATLAB® example of a counter, which is suitable for HDL code generation.
This design pattern demonstrates two best practices for writing MATLAB code for HDL code generation:
Initialize persistent variables to a specific value. In this example, an
if statement and the
function initialize the persistent variable. If the persistent variable is
not initialized then HDL code cannot be generated.
Inside a function, read persistent variables before they are modified, in order for the persistent variables to be inferred as registers.
This Simulink® model illustrates the counter modeled in this example.
To learn how to model the counter in Simulink, see Create HDL-Compatible Simulink Model.
mlhdlc_counter is a behavioral
model of a four bit synchronous up counter. The input signal,
triggers the value of the count register,
to increase by one. The counter continues to increase by one each
time the input is nonzero, until the count reaches a limit of 15.
After the counter reaches this limit, the counter returns to zero.
A persistent variable, which is initialized to zero, represents the
current value of the count. Two
determine the value of the count based on the input.
The following section of code defines the
%#codegen function count = mlhdlc_counter(enable_ctr) %four bit synchronous up counter %persistent variable for the state persistent count_val; if isempty(count_val) count_val = 0; end %counting up if enable_ctr count_val=count_val+1; %limit to four bits if count_val>15 count_val=0; end end count=count_val; end