Violation of Latency Constraint for Function Calls - 2021.1 English

Vitis HLS Messaging (UG1448)

Document ID
UG1448
Release Date
2021-06-16
Version
2021.1 English

Description

Warning: [200-893] Latency directive discarded for region %s since region contains function calls with variable latency.

This message reports that the parent function contains sub-functions of different latencies.

Explanation

The code is violating latency optimization rules. The parent function contains sub-functions of different latencies which will be added to the total parent latency as shown in the below code.

func1(...)
{
// latency of func1 = ~(func2+fun3) + ~(func1) = ~75
func2(..) # latency of this sub-func - 30
func3(...) # latency of this sub-func - 40
}

Solution

Consider taking into account the latency of the sub-function when applying the latency pragma.