The Vivado IP packager requires that the IP ports are contained within the port description of the HDL file; therefore, the IP packager does not support custom functions defined in your HDL.
The Vivado IP packager supports
standard arithmetic and logical operators to create the desired mathematical expression.
To support complex mathematical expressions, the IP packager supports XPATH functions. The following list shows the supported
XPATH functions.
- number max(number, number)
- number min(number, number)
- number sum(number, number)
- number log(base number, number)
- number pow(number, exp number)
- number floor(number)
- number ceiling(number)
- number round(number)
- number abs(number)
- boolean not(boolean)
- boolean true()
- boolean false()
For more information on XPATH and the
supported functions, see the W3Cx website.
For example, the following Verilog code declares an output port whose
width is defined from a ceil_log2 function call on the
max_count parameter. The function calculates the
log base 2 of the input and returns the smallest integer that is not less than the log result.
output [ceil_log2(max_count)-1:0] count;To convert this function into an expression that the IP packager can use,
replace the custom function with XPATH functions. This
change does not occur in the HDL because the custom function is still used, but the IP
packager uses a different mechanism for calculating the correct value. The following
XPATH expression produces the same result as the
custom function as described.
ceiling(log(2, $max_count))-1The expression contains the XPATH log() function which is passed the
base 2, and the value of the max_count parameter. The output of the
log() function is passed to the ceiling() function
to return the smallest integer not less than the log result. Finally, one is subtracted
from the final ceiling result.
For more information on setting the XPATH functions on ports in your
custom IP, see the Ports and Interfaces section.