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Two capabilities in SystemVerilog allow for the creation of a module that can produce a sine wave as an output: the ability to pass real values through port connections and DPI.
Obviously, to produce a sine wave, you need access to the sin function. This is where DPI is handy to add the math functions to your simulation. Here is an example of a package I created to contain the math functions:
task C Name = SV function name
"DPI" pure function real cos (input real rTheta);
"DPI" pure function real sin (input real rTheta);
"DPI" pure function real log (input real rVal);
"DPI" pure function real log10 (input real rVal);
endpackage : math_pkg
The import"DPI" construct defines a new function that you can use in your code that refers to a C function. In the case of the math functions listed above, they already exist in the libmath.so library built into Linux and so there is no additional code required.
Now that I have my math functions, I can create my module.
module sine_wave(output real
sampling_time = 5;
const real pi =
real time_us, time_s ;
real freq = 20;
real offset = 2.5;
real ampl = 2.5;
= #(sampling_time) ~sampling_clock;
assign sine_out =
offset + (ampl * sin(2*pi*freq*time_s));
Here I have used import in a different context. In this case import is used to make the code in my package available to the scope in which I import it. Now when I call the sinn function, it will use the DPI code from math_pkg to execute the function.
The sine_wave module also shows the use of passing a real value through a port. The output sine_out is of type real and is computed using the sin function.
SystemVerilog allows a real variable to be used as a port. The limitation is that a real variable can only be driven by a single driver. If that is a problem, you can make the module a Verilog AMS module and define the real variable as a wreal (real wire). By using wreal, you can have multiple drivers and use a variety of resolution types to solve any conflicts.
I have a signal generating sine wave. Need some code that can make sense out of it in terms of frequency, amplitude etc. and dump it in a file.
Any quick thoughts please,
If we are at it already, here is the COS function, Root of 2, Natural base LOG, LOG 2 and LOG 10 (best to have all these and the SIN function together in the same file since they may call on each other):
// COS function
function real cos;
cos = sin(x + `PI / 2.0);
// ROOT of 2
function real rootof2;
power = 0.82629586;
power = power / 10000000.0;
power = power + 1.0;
i = -23;
if (n >= 1)
power = 2.0;
i = 0;
for (i=i; i< n; i=i+1)
power = power * power;
rootof2 = power;
endfunction // rootof2
// does LOG_N of a number
function real log_n;
if (x <= 0.0)
$display("log N illegal argument:",x);
log_n = 0.0;
re = 1.0/x;
re = x;
log_2 = 0.0;
for (i=7; i>=-23; i=i-1)
if (re > rootof2(i))
re = re/rootof2(i);
log_2 = 2.0*log_2 + 1.0;
log_2 = log_2*2.0;
if (x < 1.0)
log_n = -log_2/12102203.16;
log_n = log_2/12102203.16;
endfunction // log_n
// does LOG2 of a number - using LOG_N
function real log2;
log2 = log_n(x)/log_n(2.0);
endfunction // log2
// does LOG10 of a number - using LOG_N
function real log10;
log10 = log_n(x)/log_n(10.0);
endfunction // log10
That works great! I just put your code in my package in place of the "import...sin" and it worked like a champ.
Thanks for sharing,
Hi Tim, I had this same problem before and used something else I found:
A function that has a sin approximation, input is real, and you invoke the function at the desired clock rate and supplying the desired input, here is the code:
`define PI 3.14159265
function real sin;
sign = 1.0;
x1 = x;
x1 = -x1;
sign = -1.0;
while (x1 > `PI/2.0)
x1 = x1 - `PI;
sign = -1.0*sign;
y = x1*2/`PI;
y2 = y*y;
y3 = y*y2;
y5 = y3*y2;
y7 = y5*y2;
sum = 1.570794*y - 0.645962*y3 +
0.079692*y5 - 0.004681712*y7;
sin = sign*sum;
endfunction // sin