[CodeStudy] RocketChip Optional Bundle

Published: October 08, 2020 by SingularityKChen (Last updated: October 08, 2020 )

• Categories:
• CodeStudy 12

• Tags:
• Chisel 22
• RocketChip 1

• Optional Bundle
  • Optional Basic
  • Optional Functions
  • Making Bundle Optional

Optional Bundle

rocket-playground/rocketchip/src/main/scala/util/LanePositionedQueue.scala

Sometimes, we need some ports but sometimes not. One method is extend one base class, or with one trait bundle. However, most time they're not that configurable.

Another way is making this bundle be Optional.

Optional Basic

Optional means one parameter is either None or has some values.

For instance, in Optional[T], if it contains some values, then its Some[T], otherwise, that's None.

Optional Functions

You can use get() to access Some[T] or None. Also, if you need one default value when None, then you can use getOrElse().

Making Bundle Optional

val free = if (args.free) Some(Flipped(Decoupled(UInt(depthBitsU.W)))) else None
val rewind = if (args.rewind) Some(Input(Bool())) else None

Simply wrapping your bundle with Some().

When you want to get this value, you need to add .get() or .getOrElse().

val f = q.io.free.get()
val doRewind = io.rewind.getOrElse(false.B)

In this case, bundles are more reusable and configurable.