set_directive_protocol

Description

This commands specifies a region of code, a protocol region, in which no clock operations will be inserted by Vitis HLS unless explicitly specified in the code. Vitis HLS will not insert any clocks between operations in the region, including those which read from or write to function arguments. The order of read and writes will therefore be strictly followed in the synthesized RTL.

A region of code can be created in the C code by enclosing the region in braces "{ }" and naming it. The following defines a region named io_section:
io_section:{
...
lines of code
...
}

A clock operation may be explicitly specified in C code using an ap_wait() statement, and may be specified in C++ code by using the wait() statement. The ap_wait and wait statements have no effect on the simulation of the design.

Syntax

set_directive_protocol [OPTIONS] <location>

The <location> specifies the location (in the format function[/label]) at which the protocol region is defined.

Options

-mode [floating | fixed]
  • floating: Lets code statements outside the protocol region overlap and execute in parallel with statements in the protocol region in the final RTL. The protocol region remains cycle accurate, but outside operations can occur at the same time. This is the default mode.
  • fixed: The fixed mode ensures that statements outside the protocol region do not execute in parallel with the protocol region.

Example

The example code defines a protocol region, io_section in function foo. The following directive defines that region as a fixed mode protocol region:
set_directive_protocol -mode fixed foo/io_section

See Also