How to define and use a distributable function

• version

  1.1.1

• scope

  Example.

  This code is provided as example code for a user to base their code on.

• description

  How to define and use a distributable function

• boards

  Unless otherwise specified, this example runs on the SliceKIT Core Board, but can easily be run on any XMOS device by using a different XN file.

If a task is a never-ending loop containing a single select (like a combinable function) that only has cases responding to interface messages, the function can be marked as distributable. For example:

[[distributable]]
void port_wiggler(server interface wiggle_if c, port p)
{
  // This task waits for a message on the interface c and
  // wiggles the port p the required number of times.
  while (1) {
    select {
    case c.wiggle(int n):
      printstrln("Wiggling port.");
      for (int i=0;i<n;i++) {
        p <: 1;
        p <: 0;
      }
      break;
    case c.finish():
      return;
    }
  }
}

A distributable task can be distributed within a par. This means that the task will not run on any particular core but will be run on the core of the task that calls to it.

int main() {
  interface wiggle_if c;
  par {
    task1(c);
    [[distribute]] port_wiggler(c, p);
  }
  return 0;
}

A distributed task must be on the same tile as the tasks it is connected to.