{-# LANGUAGE DataKinds #-}
{-# LANGUAGE NumericUnderscores #-}

module Fetch(
  fetchInstruction,
  FetchResult(..),
  ) where

import Clash.Prelude
import Types(Mem, Addr, Insn)
import Bus(ReadResponse, WriteResponse, read)
import Bus(Peripherals(..))
import BusTypes(
  ReadRequest(..),
  TransactionSize(..),
  BusVal(..),
  BusError(..))
import Exceptions(Exception(..), exceptionCode, isSynchronousException)

import GHC.IO (IO)
import GHC.Base (Applicative(pure))

data FetchResult  = Instruction Insn
                   | InstructionException Exception

fetchInstruction :: Peripherals -> Addr -> IO FetchResult
fetchInstruction peripherals addr =
  do
    readReasponse <-Bus.read (BusTypes.Request addr BusTypes.SizeFullWord) peripherals
    case readReasponse of
      Right (BusFullWord insn) ->
        pure $ Instruction insn
      Left  UnAligned ->
        pure $ InstructionException InstructionAddressMisaligned
      Left  UnMapped ->
        pure $ InstructionException InstructionAccessFault
      Right _ ->
        pure $ InstructionException InstructionAccessFault