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General informations

This repository contain a Wishbone VexRiscv configuration in :
src/main/scala/vexriscv GenCoreDefault.scala

  • RV32IM
  • 5 stage : F -> D -> E -> M -> WB + fully bypassed
  • single cycle ADD/SUB/Bitwise/Shift ALU
  • i$ : 4 kB 1 way
  • d$ : 4 kB 1 way + victim buffer
  • Branch prediction => Static
  • branch/jump done in the M stage
  • memory load values are bypassed in the WB stage (late result)
  • 33 cycle division with bypassing in the M stage (late result)
  • single cycle multiplication with bypassing in the WB stage (late result)
  • Light subset of the RISC-V machine CSR with an 32 bits external interrupt extension
  • Available in normal an -Debug, with the Debug bus exposed

Requirements

  • Java 8
  • SBT (Scala build tool, kind of make file but for scala)

On Debian =>

sudo add-apt-repository -y ppa:openjdk-r/ppa
sudo apt-get update
sudo apt-get install openjdk-8-jdk -y
sudo update-alternatives --config java
sudo update-alternatives --config javac

echo "deb https://dl.bintray.com/sbt/debian /" | sudo tee -a /etc/apt/sources.list.d/sbt.list
sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 2EE0EA64E40A89B84B2DF73499E82A75642AC823
sudo apt-get update
sudo apt-get install sbt -y

Usages

Generate the verilog from default core configuration :
sbt "runMain vexriscv.GenCoreDefault"

Note : The first time you run it it will take time to download all dependancies (including Scala itself). You have time to drink a coffee.

Cleaning SBT :
sbt clean reload
Updating the VexRiscv :

The build.sbt file is the "makefile" of this scala project. In it you can update the following lines to change the VexRiscv version :

lazy val vexRiscv = RootProject(uri("VexRiscvGitRepositoryUrl[#commitHash]"))

If you want you can also use a local folder as a VexRiscv version :

lazy val vexRiscv = RootProject(file("local/path/to/the/VexRiscv"))
Configuration options :

VexRiscv supports several configuration options:

  • -d: If specified, builds VexRiscv with a debug bus
  • -dCacheSize=cacheSize: Specify the data cache size. Defaults to 4096.
  • -iCacheSize=cacheSize: Specify the instruction cache size. Defaults to 4096.
  • **-mulDiv=**true/false: Include multiplication/division circuitry.
  • **-singleCycleMulDiv=**true/false: If this option is true, multiplication, division, and shifting are optimized for speed. Otherwise, they are optimized for area.

As an example, you can build a VexRiscv core with a 2048-byte cache size by running:

sbt "runMain vexriscv.GenCoreDefault -d --iCacheSize=2048"

VexRiscv-Lite.v was built using:

sbt "runMain vexriscv.GenCoreDefault --iCacheSize 2048 --dCacheSize 0 --mulDiv true --singleCycleMulDiv false"