Permalink
Find file
Fetching contributors…
Cannot retrieve contributors at this time
64 lines (52 sloc) 2.34 KB
module Hardware.CPU (CPUState, Halt(..), cpu) where
import CLaSH.Prelude
import Hardware.StackMachine (State(Initializing),
step1, step2, outputOf, terminal)
import Hardware.MMU (Pending, RAMStatus(NoUpdate), RAMAction(X),
initiate, next, service, check)
import Hardware.Model (Output(..))
-- Halt?
data Halt = DoHalt | Don'tHalt deriving Show
-- Are we waiting for a single memory action (read/write/etc.) to complete?
data Waiting = No | Yes deriving Show
-- We need to keep track of the evaluator state as well as the MMU state.
data CPUState = CPU State Pending Waiting deriving Show
-- The state of the MMU when the CPU is initialized.
-- If you look at the definition of step1, this corresponds
-- to loading the SKI combinator from 0x0. This is where the
-- root of the program tree goes.
bootup :: Pending
bootup = initiate (step1 Initializing)
-- The transition function of the CPU.
step :: CPUState -> RAMStatus -> (CPUState, RAMAction, Maybe Output)
step (CPU state pending Yes) NoUpdate = (CPU state pending Yes, X, Nothing)
step (CPU state pending _ ) update = (CPU state' pending'' waiting', action, output)
where
pending' = service pending update
result = check pending' -- Did we finish a transaction?
state' = case result of
Nothing -> state -- Memory transaction did not finish.
Just result -> step2 state result -- Finished! Calculate new state.
pending'' = case result of
Nothing -> pending' -- We can keep servicing this transaction
Just _ -> initiate (step1 state') -- Start servicing new transaction.
action = next pending''
output = case result of
Nothing -> Nothing -- We only output if we're in a brand new state
Just _ -> outputOf state' -- New state, new output.
waiting' = case action of
X -> No
_ -> Yes
checkIfDone :: CPUState -> Halt
checkIfDone (CPU state _ _) = if terminal state then DoHalt else Don'tHalt
cpu :: Signal RAMStatus -> Signal (RAMAction, Maybe Output, Halt)
cpu ramstatus = bundle (action, output, halt)
where
state :: Signal CPUState
state = register (CPU Initializing bootup No) state'
state' :: Signal CPUState
action :: Signal RAMAction
output :: Signal (Maybe Output)
(state', action, output) = unbundle $ step <$> state <*> ramstatus
halt :: Signal Halt
halt = checkIfDone <$> state