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

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

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

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