Note: This project is a simple test project to use Chisel!
Extracted from the Chisel doc:
We recommend LTS releases Java 8 and Java 11. You can install the JDK as recommended by your operating system, or use the prebuilt binaries from AdoptOpenJDK.
SBT is the most common build tool in the Scala community. You can download it here.
Mill is another Scala/Java build tool without obscure DSL like SBT. You can download it here
Simply running sbt run should install the dependencies and generate the Verilog implementations of both RIMI verifications in the directory generated/. To run tests, sbt test launches the two tests and generates their waveform in the directory test_run_dir/.
The RIMI isolation model adds a Domain Memory Protection (DMP) unit on top of the existing Physical Memory Protection (PMP). It uses duplicated memory access instructions linked to a given domain and additional instructions to change domains. The article can be found here and this repository is the first step in an inclusion in the Rocket CPU
Both verifications are simple as they simply check the equality between:
- the decoded code domain of an instruction and the current domain read from a CSR
- the decoded data domain of an instruction and the current domain read from a CSR
The Chisel code is the following:
/**
* Performs the first check for the RIMI isolation model.
* This checks simply asserts that the decoded instruction
* is executing in its dedicated domain.
* Note: This check should happen during the decode stage
* and interrupt the execution if domains do not match.
*/
class RIMI1 extends Module {
val io = IO(new Bundle {
val instrDomain = Input(UInt(3.W)) // Decoder
val currentDomain = Input(UInt(3.W)) // CSR read
val out = Output(Bool())
})
io.out := io.instrDomain === io.currentDomain
}
/**
* Performs the second check for the RIMI isolation model.
* This check is performed along with the PMP checks without
* taking precedence on them. The check here compares the
* domain affected to the pmp region (in dmpcfg) with the
* current domain.
*/
class RIMI2() extends Module {
val io = IO(new Bundle {
val currentDomain = Input(UInt(3.W)) // CSR read
val dmpConfigDomain = Input(UInt(3.W)) // CSR read (?)
val out = Output(Bool())
})
io.out := io.currentDomain === io.dmpConfigDomain
}- When in the pipeline are CSRs read/written?
- When in the pipeline are the PMP CSRs read?
- When and where is the PMP region checked?
- What verification cost can be hidden in parallel of a pipeline stage?