[Chisel] About Queue

Introduction

If you want to use a queue to pass data in Chisel, Queue class is provided.

I will explain how to use it.

Basic usage

Definition

val buf = Module(new Queue(gen = new UInt, entries = 10))

For 'gen', specify an instance of the type of data to be passed. For 'entries', specify the upper limit on the number of data that can be queued.

Input/output

Connect the data to be input to io.enq.bits.

buf.io.enq.bits := data

Set 'valid' and 'ready' to true when input data.

buf.io.enq.valid := true.B
buf.io.enq.ready := true.B

Similarly, connect io.deq.bits to the extraction destination and set 'valid' and 'ready'.

eXUnit.io.input := buf.io.deq.bits
buf.io.deq.valid := true.B
buf.io.deq.ready := true.B

In practice, since you want to use a queue, you would like to do something like "take something out of the queue when a certain condition is met.''

For example, when a calculation is completed, the next instruction is taken out of the instruction queue.

In such a case, you can define a "condition signal" and connect it to ready.

var complete = Wire(Bool())
・・・ //complete = true.B when calculation completes
buf.io.deq.valid := complete

This is a bit difficult to understand for a software developer's point of view, that instead of "calling the enq() method when a certain condition is met," control is done using signal values like this.

Reference

https://github.com/chipsalliance/chisel/blob/main/src/main/scala/chisel3/util/Decoupled.scala