Pipelines

ROHD has a built-in syntax for handling pipelines in a simple & refactorable way. The below example shows a three-stage pipeline which adds 1 three times. Note that Pipeline consumes a clock and a list of stages, which are each a List<Conditional> Function(PipelineStageInfo p), where PipelineStageInfo has information on the value of a given signal in that stage. The List<Conditional> the same type of procedural code that can be placed in Combinational.

Logic a;
var pipeline = Pipeline(clk,
  stages: [
    (p) => [
      // the first time `get` is called, `a` is automatically pipelined
      p.get(a) < p.get(a) + 1
    ],
    (p) => [
      p.get(a) < p.get(a) + 1
    ],
    (p) => [
      p.get(a) < p.get(a) + 1
    ],
  ]
);
var b = pipeline.get(a); // the output of the pipeline

This pipeline is very easy to refactor. If we wanted to merge the last two stages, we could simply rewrite it as:

Logic a;
var pipeline = Pipeline(clk,
  stages: [
    (p) => [
      p.get(a) < p.get(a) + 1
    ],
    (p) => [
      p.get(a) < p.get(a) + 1,
      p.get(a) < p.get(a) + 1
    ],
  ]
);
var b = pipeline.get(a);

You can also optionally add stalls and reset values for signals in the pipeline. Any signal not accessed via the PipelineStageInfo object is just accessed as normal, so other logic can optionally sit outside of the pipeline object.

ROHD also includes a version of Pipeline that supports a ready/valid protocol called ReadyValidPipeline. The syntax looks the same, but has some additional parameters for readys and valids.