Parameters and Keys

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Create file and import dependencies

Create a new text file in location:

p-chipyard/generators/chipyard/src/main/scala/example

and call it JustRead.scala. Open it (we recommend using Sublime) and type these lines:

package chipyard.example

import chisel3._
import chisel3.util._
import chisel3.experimental.{IntParam, BaseModule}
import freechips.rocketchip.subsystem.BaseSubsystem
import freechips.rocketchip.config.{Parameters, Field, Config}
import freechips.rocketchip.diplomacy._
import freechips.rocketchip.regmapper.{HasRegMap, RegField}
import freechips.rocketchip.tilelink._
import freechips.rocketchip.util.UintIsOneOf

The first one tells that this file will be part of the chipyard.example package, whereas the rest just import a bunch of Chisel/Diplomacy/TileLink/RocketChip stuff. Any discussion on those topics is beyond this write-up, but here you can find some really good documentation on all of them.

Parameters

First, we need the case class with a name forged from the name of our project suffixed by Params (sometimes it’s suffixed with Config, instead). In our simplest of designs let’s have just two parameters: the offset address where the memory mapping starts (address) and the width of the data our processor will be just reading (width). Here’s how we do that:

case class JustReadParams(
	address: BigInt = 0x2000,
	width: Int = 32)

both of these default values are pretty much arbitrary, so feel free to play around with them later on.

Key

The second thing is the Key – again we suffix the Key to the name of the project and do this:

case object JustReadKey extends Field[Option[JustReadParams]](None)

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