The STABLE pragma is applied to arguments of a DATAFLOW or PIPELINE region and is used to indicate that an input or output of this region can be ignored when generating the synchronizations at entry and exit of the DATAFLOW region. This means that the reading processes (resp. read accesses) of that argument do not need to be part of the “first stage” of the task-level (resp. fine-grain) pipeline for inputs, and the writing process (resp. write accesses) do not need to be part of the last stage of the task-level (resp. fine-grain) pipeline for outputs.
The pragma can be specified at any point in the hierarchy, on a scalar or an array, and automatically applies to all the DATAFLOW or PIPELINE regions below that point. The effect of STABLE for an input is that a DATAFLOW or PIPELINE region can start another iteration even though the value of the previous iteration has not been read yet. For an output, this implies that a write of the next iteration can occur although the previous iteration is not done.
#pragma HLS stable variable=<a>
- Specifies the variable to which the STABLE pragma is applied.
In the following example, without the STABLE pragma,
proc2 would be
synchronized to acknowledge the reading of their inputs (including
A). With the pragma,
A is no longer considered
as an input that needs synchronization.
void dataflow_region(int A[...], int B[…] ... #pragma HLS stable variable=A #pragma HLS dataflow proc1(...); proc2(A, ...);