System.GPIO.Linux.Sysfs.Monad

Monad type classes and instances for Linux sysfs GPIO operations.

MonadSysfs class

class Monad m => MonadSysfs m where

A type class for monads which implement (or mock) low-level Linux sysfs GPIO operations.

Methods

doesDirectoryExist :: FilePath -> m Bool

Equivalent to doesDirectoryExist.

doesFileExist :: FilePath -> m Bool

Equivalent to doesFileExist.

getDirectoryContents :: FilePath -> m [FilePath]

Equivalent to getDirectoryContents.

readFile :: FilePath -> m ByteString

Equivalent to readFile.

writeFile :: FilePath -> ByteString -> m ()

Equivalent to writeFile.

unlockedWriteFile :: FilePath -> ByteString -> m ()

sysfs control files which are global shared resources may be written simultaneously by multiple threads. This is fine -- sysfs can handle this -- but Haskell's writeFile cannot, as it locks the file and prevents multiple writers. We don't want this behavior, so we use low-level operations to get around it.

pollFile :: FilePath -> Int -> m CInt

Poll a sysfs file for reading, as in POSIX.1-2001 poll(2).

Note that the implementation of this action is only guaranteed to work for sysfs files, which have a peculiar way of signaling readiness for reads. Do not use it for any other purpose.

doesDirectoryExist :: (MonadTrans t, MonadSysfs m', t m' ~ m) => FilePath -> m Bool

Equivalent to doesDirectoryExist.

doesFileExist :: (MonadTrans t, MonadSysfs m', t m' ~ m) => FilePath -> m Bool

Equivalent to doesFileExist.

getDirectoryContents :: (MonadTrans t, MonadSysfs m', t m' ~ m) => FilePath -> m [FilePath]

Equivalent to getDirectoryContents.

readFile :: (MonadTrans t, MonadSysfs m', t m' ~ m) => FilePath -> m ByteString

Equivalent to readFile.

writeFile :: (MonadTrans t, MonadSysfs m', t m' ~ m) => FilePath -> ByteString -> m ()

Equivalent to writeFile.

unlockedWriteFile :: (MonadTrans t, MonadSysfs m', t m' ~ m) => FilePath -> ByteString -> m ()

sysfs control files which are global shared resources may be written simultaneously by multiple threads. This is fine -- sysfs can handle this -- but Haskell's writeFile cannot, as it locks the file and prevents multiple writers. We don't want this behavior, so we use low-level operations to get around it.

pollFile :: (MonadTrans t, MonadSysfs m', t m' ~ m) => FilePath -> Int -> m CInt

Poll a sysfs file for reading, as in POSIX.1-2001 poll(2).

Note that the implementation of this action is only guaranteed to work for sysfs files, which have a peculiar way of signaling readiness for reads. Do not use it for any other purpose.

Instances

MonadSysfs m => MonadSysfs (MaybeT m)

Methods

doesDirectoryExist :: FilePath -> MaybeT m Bool

doesFileExist :: FilePath -> MaybeT m Bool

getDirectoryContents :: FilePath -> MaybeT m [FilePath]

readFile :: FilePath -> MaybeT m ByteString

writeFile :: FilePath -> ByteString -> MaybeT m ()

unlockedWriteFile :: FilePath -> ByteString -> MaybeT m ()

pollFile :: FilePath -> Int -> MaybeT m CInt

MonadSysfs m => MonadSysfs (CatchT m)

Methods

doesDirectoryExist :: FilePath -> CatchT m Bool

doesFileExist :: FilePath -> CatchT m Bool

getDirectoryContents :: FilePath -> CatchT m [FilePath]

readFile :: FilePath -> CatchT m ByteString

writeFile :: FilePath -> ByteString -> CatchT m ()

unlockedWriteFile :: FilePath -> ByteString -> CatchT m ()

pollFile :: FilePath -> Int -> CatchT m CInt

MonadSysfs m => MonadSysfs (ListT m)

Methods

doesDirectoryExist :: FilePath -> ListT m Bool

doesFileExist :: FilePath -> ListT m Bool

getDirectoryContents :: FilePath -> ListT m [FilePath]

readFile :: FilePath -> ListT m ByteString

writeFile :: FilePath -> ByteString -> ListT m ()

unlockedWriteFile :: FilePath -> ByteString -> ListT m ()

pollFile :: FilePath -> Int -> ListT m CInt

MonadSysfs m => MonadSysfs (NoLoggingT m)

Methods

doesDirectoryExist :: FilePath -> NoLoggingT m Bool

doesFileExist :: FilePath -> NoLoggingT m Bool

getDirectoryContents :: FilePath -> NoLoggingT m [FilePath]

readFile :: FilePath -> NoLoggingT m ByteString

writeFile :: FilePath -> ByteString -> NoLoggingT m ()

unlockedWriteFile :: FilePath -> ByteString -> NoLoggingT m ()

pollFile :: FilePath -> Int -> NoLoggingT m CInt

MonadSysfs m => MonadSysfs (LoggingT m)

Methods

doesDirectoryExist :: FilePath -> LoggingT m Bool

doesFileExist :: FilePath -> LoggingT m Bool

getDirectoryContents :: FilePath -> LoggingT m [FilePath]

readFile :: FilePath -> LoggingT m ByteString

writeFile :: FilePath -> ByteString -> LoggingT m ()

unlockedWriteFile :: FilePath -> ByteString -> LoggingT m ()

pollFile :: FilePath -> Int -> LoggingT m CInt

MockM m => MonadSysfs (SysfsMockT m)

Methods

doesDirectoryExist :: FilePath -> SysfsMockT m Bool

doesFileExist :: FilePath -> SysfsMockT m Bool

getDirectoryContents :: FilePath -> SysfsMockT m [FilePath]

readFile :: FilePath -> SysfsMockT m ByteString

writeFile :: FilePath -> ByteString -> SysfsMockT m ()

unlockedWriteFile :: FilePath -> ByteString -> SysfsMockT m ()

pollFile :: FilePath -> Int -> SysfsMockT m CInt

(MonadIO m, MonadThrow m) => MonadSysfs (SysfsIOT m)

Methods

doesDirectoryExist :: FilePath -> SysfsIOT m Bool

doesFileExist :: FilePath -> SysfsIOT m Bool

getDirectoryContents :: FilePath -> SysfsIOT m [FilePath]

readFile :: FilePath -> SysfsIOT m ByteString

writeFile :: FilePath -> ByteString -> SysfsIOT m ()

unlockedWriteFile :: FilePath -> ByteString -> SysfsIOT m ()

pollFile :: FilePath -> Int -> SysfsIOT m CInt

(MonadSysfs m, Monoid w) => MonadSysfs (WriterT w m)

Methods

doesDirectoryExist :: FilePath -> WriterT w m Bool

doesFileExist :: FilePath -> WriterT w m Bool

getDirectoryContents :: FilePath -> WriterT w m [FilePath]

readFile :: FilePath -> WriterT w m ByteString

writeFile :: FilePath -> ByteString -> WriterT w m ()

unlockedWriteFile :: FilePath -> ByteString -> WriterT w m ()

pollFile :: FilePath -> Int -> WriterT w m CInt

(MonadSysfs m, Monoid w) => MonadSysfs (WriterT w m)

Methods

doesDirectoryExist :: FilePath -> WriterT w m Bool

doesFileExist :: FilePath -> WriterT w m Bool

getDirectoryContents :: FilePath -> WriterT w m [FilePath]

readFile :: FilePath -> WriterT w m ByteString

writeFile :: FilePath -> ByteString -> WriterT w m ()

unlockedWriteFile :: FilePath -> ByteString -> WriterT w m ()

pollFile :: FilePath -> Int -> WriterT w m CInt

MonadSysfs m => MonadSysfs (StateT s m)

Methods

doesDirectoryExist :: FilePath -> StateT s m Bool

doesFileExist :: FilePath -> StateT s m Bool

getDirectoryContents :: FilePath -> StateT s m [FilePath]

readFile :: FilePath -> StateT s m ByteString

writeFile :: FilePath -> ByteString -> StateT s m ()

unlockedWriteFile :: FilePath -> ByteString -> StateT s m ()

pollFile :: FilePath -> Int -> StateT s m CInt

MonadSysfs m => MonadSysfs (StateT s m)

Methods

doesDirectoryExist :: FilePath -> StateT s m Bool

doesFileExist :: FilePath -> StateT s m Bool

getDirectoryContents :: FilePath -> StateT s m [FilePath]

readFile :: FilePath -> StateT s m ByteString

writeFile :: FilePath -> ByteString -> StateT s m ()

unlockedWriteFile :: FilePath -> ByteString -> StateT s m ()

pollFile :: FilePath -> Int -> StateT s m CInt

MonadSysfs m => MonadSysfs (ExceptT e m)

Methods

doesDirectoryExist :: FilePath -> ExceptT e m Bool

doesFileExist :: FilePath -> ExceptT e m Bool

getDirectoryContents :: FilePath -> ExceptT e m [FilePath]

readFile :: FilePath -> ExceptT e m ByteString

writeFile :: FilePath -> ByteString -> ExceptT e m ()

unlockedWriteFile :: FilePath -> ByteString -> ExceptT e m ()

pollFile :: FilePath -> Int -> ExceptT e m CInt

MonadSysfs m => MonadSysfs (IdentityT * m)

Methods

doesDirectoryExist :: FilePath -> IdentityT * m Bool

doesFileExist :: FilePath -> IdentityT * m Bool

getDirectoryContents :: FilePath -> IdentityT * m [FilePath]

readFile :: FilePath -> IdentityT * m ByteString

writeFile :: FilePath -> ByteString -> IdentityT * m ()

unlockedWriteFile :: FilePath -> ByteString -> IdentityT * m ()

pollFile :: FilePath -> Int -> IdentityT * m CInt

MonadSysfs m => MonadSysfs (ReaderT * r m)

Methods

doesDirectoryExist :: FilePath -> ReaderT * r m Bool

doesFileExist :: FilePath -> ReaderT * r m Bool

getDirectoryContents :: FilePath -> ReaderT * r m [FilePath]

readFile :: FilePath -> ReaderT * r m ByteString

writeFile :: FilePath -> ByteString -> ReaderT * r m ()

unlockedWriteFile :: FilePath -> ByteString -> ReaderT * r m ()

pollFile :: FilePath -> Int -> ReaderT * r m CInt

MonadSysfs m => MonadSysfs (ContT * r m)

Methods

doesDirectoryExist :: FilePath -> ContT * r m Bool

doesFileExist :: FilePath -> ContT * r m Bool

getDirectoryContents :: FilePath -> ContT * r m [FilePath]

readFile :: FilePath -> ContT * r m ByteString

writeFile :: FilePath -> ByteString -> ContT * r m ()

unlockedWriteFile :: FilePath -> ByteString -> ContT * r m ()

pollFile :: FilePath -> Int -> ContT * r m CInt

(MonadSysfs m, Monoid w) => MonadSysfs (RWST r w s m)

Methods

doesDirectoryExist :: FilePath -> RWST r w s m Bool

doesFileExist :: FilePath -> RWST r w s m Bool

getDirectoryContents :: FilePath -> RWST r w s m [FilePath]

readFile :: FilePath -> RWST r w s m ByteString

writeFile :: FilePath -> ByteString -> RWST r w s m ()

unlockedWriteFile :: FilePath -> ByteString -> RWST r w s m ()

pollFile :: FilePath -> Int -> RWST r w s m CInt

(MonadSysfs m, Monoid w) => MonadSysfs (RWST r w s m)

Methods

doesDirectoryExist :: FilePath -> RWST r w s m Bool

doesFileExist :: FilePath -> RWST r w s m Bool

getDirectoryContents :: FilePath -> RWST r w s m [FilePath]

readFile :: FilePath -> RWST r w s m ByteString

writeFile :: FilePath -> ByteString -> RWST r w s m ()

unlockedWriteFile :: FilePath -> ByteString -> RWST r w s m ()

pollFile :: FilePath -> Int -> RWST r w s m CInt

GPIO via sysfs

newtype PinDescriptor

The sysfs pin handle type. Currently it's just a newtype wrapper around a Pin. The constructor is exported for convenience, but note that the implementation may change in future versions of the package.

Constructors

PinDescriptor

Fields

• _pin :: Pin

Instances

Eq PinDescriptor

Methods

(==) :: PinDescriptor -> PinDescriptor -> Bool

(/=) :: PinDescriptor -> PinDescriptor -> Bool

Ord PinDescriptor

Methods

compare :: PinDescriptor -> PinDescriptor -> Ordering

(<) :: PinDescriptor -> PinDescriptor -> Bool

(<=) :: PinDescriptor -> PinDescriptor -> Bool

(>) :: PinDescriptor -> PinDescriptor -> Bool

(>=) :: PinDescriptor -> PinDescriptor -> Bool

max :: PinDescriptor -> PinDescriptor -> PinDescriptor

min :: PinDescriptor -> PinDescriptor -> PinDescriptor

Show PinDescriptor

Methods

showsPrec :: Int -> PinDescriptor -> ShowS

show :: PinDescriptor -> String

showList :: [PinDescriptor] -> ShowS

(MonadMask m, ThrowCatchSysfsM m) => MonadGpio PinDescriptor (SysfsGpioT m)

Methods

pins :: SysfsGpioT m [Pin]

pinCapabilities :: Pin -> SysfsGpioT m PinCapabilities

openPin :: Pin -> SysfsGpioT m PinDescriptor

closePin :: PinDescriptor -> SysfsGpioT m ()

getPinDirection :: PinDescriptor -> SysfsGpioT m PinDirection

getPinInputMode :: PinDescriptor -> SysfsGpioT m PinInputMode

setPinInputMode :: PinDescriptor -> PinInputMode -> SysfsGpioT m ()

getPinOutputMode :: PinDescriptor -> SysfsGpioT m PinOutputMode

setPinOutputMode :: PinDescriptor -> PinOutputMode -> PinValue -> SysfsGpioT m ()

readPin :: PinDescriptor -> SysfsGpioT m PinValue

pollPin :: PinDescriptor -> SysfsGpioT m PinValue

pollPinTimeout :: PinDescriptor -> Int -> SysfsGpioT m (Maybe PinValue)

writePin :: PinDescriptor -> PinValue -> SysfsGpioT m ()

togglePin :: PinDescriptor -> SysfsGpioT m PinValue

getPinInterruptMode :: PinDescriptor -> SysfsGpioT m PinInterruptMode

setPinInterruptMode :: PinDescriptor -> PinInterruptMode -> SysfsGpioT m ()

getPinActiveLevel :: PinDescriptor -> SysfsGpioT m PinActiveLevel

setPinActiveLevel :: PinDescriptor -> PinActiveLevel -> SysfsGpioT m ()

togglePinActiveLevel :: PinDescriptor -> SysfsGpioT m PinActiveLevel

newtype SysfsGpioT m a

An instance of MonadGpio which translates actions in that monad to operations on Linux's native sysfs GPIO interface.

Constructors

SysfsGpioT

Fields

• runSysfsGpioT :: m a

Instances

MonadTrans SysfsGpioT

Methods

lift :: Monad m => m a -> SysfsGpioT m a

MonadTransControl SysfsGpioT

Associated Types

type StT (SysfsGpioT :: (* -> *) -> * -> *) a :: *

Methods

liftWith :: Monad m => (Run SysfsGpioT -> m a) -> SysfsGpioT m a

restoreT :: Monad m => m (StT SysfsGpioT a) -> SysfsGpioT m a

MonadRWS r w s m => MonadRWS r w s (SysfsGpioT m)

MonadBaseControl b m => MonadBaseControl b (SysfsGpioT m)

Associated Types

type StM (SysfsGpioT m :: * -> *) a :: *

Methods

liftBaseWith :: (RunInBase (SysfsGpioT m) b -> b a) -> SysfsGpioT m a

restoreM :: StM (SysfsGpioT m) a -> SysfsGpioT m a

MonadBase b m => MonadBase b (SysfsGpioT m)

Methods

liftBase :: b α -> SysfsGpioT m α

MonadError e m => MonadError e (SysfsGpioT m)

Methods

throwError :: e -> SysfsGpioT m a

catchError :: SysfsGpioT m a -> (e -> SysfsGpioT m a) -> SysfsGpioT m a

MonadReader r m => MonadReader r (SysfsGpioT m)

Methods

ask :: SysfsGpioT m r

local :: (r -> r) -> SysfsGpioT m a -> SysfsGpioT m a

reader :: (r -> a) -> SysfsGpioT m a

MonadState s m => MonadState s (SysfsGpioT m)

Methods

get :: SysfsGpioT m s

put :: s -> SysfsGpioT m ()

state :: (s -> (a, s)) -> SysfsGpioT m a

MonadWriter w m => MonadWriter w (SysfsGpioT m)

Methods

writer :: (a, w) -> SysfsGpioT m a

tell :: w -> SysfsGpioT m ()

listen :: SysfsGpioT m a -> SysfsGpioT m (a, w)

pass :: SysfsGpioT m (a, w -> w) -> SysfsGpioT m a

(MonadMask m, ThrowCatchSysfsM m) => MonadGpio PinDescriptor (SysfsGpioT m)

Methods

pins :: SysfsGpioT m [Pin]

pinCapabilities :: Pin -> SysfsGpioT m PinCapabilities

openPin :: Pin -> SysfsGpioT m PinDescriptor

closePin :: PinDescriptor -> SysfsGpioT m ()

getPinDirection :: PinDescriptor -> SysfsGpioT m PinDirection

getPinInputMode :: PinDescriptor -> SysfsGpioT m PinInputMode

setPinInputMode :: PinDescriptor -> PinInputMode -> SysfsGpioT m ()

getPinOutputMode :: PinDescriptor -> SysfsGpioT m PinOutputMode

setPinOutputMode :: PinDescriptor -> PinOutputMode -> PinValue -> SysfsGpioT m ()

readPin :: PinDescriptor -> SysfsGpioT m PinValue

pollPin :: PinDescriptor -> SysfsGpioT m PinValue

pollPinTimeout :: PinDescriptor -> Int -> SysfsGpioT m (Maybe PinValue)

writePin :: PinDescriptor -> PinValue -> SysfsGpioT m ()

togglePin :: PinDescriptor -> SysfsGpioT m PinValue

getPinInterruptMode :: PinDescriptor -> SysfsGpioT m PinInterruptMode

setPinInterruptMode :: PinDescriptor -> PinInterruptMode -> SysfsGpioT m ()

getPinActiveLevel :: PinDescriptor -> SysfsGpioT m PinActiveLevel

setPinActiveLevel :: PinDescriptor -> PinActiveLevel -> SysfsGpioT m ()

togglePinActiveLevel :: PinDescriptor -> SysfsGpioT m PinActiveLevel

Monad m => Monad (SysfsGpioT m)

Methods

(>>=) :: SysfsGpioT m a -> (a -> SysfsGpioT m b) -> SysfsGpioT m b

(>>) :: SysfsGpioT m a -> SysfsGpioT m b -> SysfsGpioT m b

return :: a -> SysfsGpioT m a

fail :: String -> SysfsGpioT m a

Functor m => Functor (SysfsGpioT m)

Methods

fmap :: (a -> b) -> SysfsGpioT m a -> SysfsGpioT m b

(<$) :: a -> SysfsGpioT m b -> SysfsGpioT m a

MonadFix m => MonadFix (SysfsGpioT m)

Methods

mfix :: (a -> SysfsGpioT m a) -> SysfsGpioT m a

Applicative m => Applicative (SysfsGpioT m)

Methods

pure :: a -> SysfsGpioT m a

(<*>) :: SysfsGpioT m (a -> b) -> SysfsGpioT m a -> SysfsGpioT m b

(*>) :: SysfsGpioT m a -> SysfsGpioT m b -> SysfsGpioT m b

(<*) :: SysfsGpioT m a -> SysfsGpioT m b -> SysfsGpioT m a

Alternative m => Alternative (SysfsGpioT m)

Methods

empty :: SysfsGpioT m a

(<|>) :: SysfsGpioT m a -> SysfsGpioT m a -> SysfsGpioT m a

some :: SysfsGpioT m a -> SysfsGpioT m [a]

many :: SysfsGpioT m a -> SysfsGpioT m [a]

MonadPlus m => MonadPlus (SysfsGpioT m)

Methods

mzero :: SysfsGpioT m a

mplus :: SysfsGpioT m a -> SysfsGpioT m a -> SysfsGpioT m a

MonadIO m => MonadIO (SysfsGpioT m)

Methods

liftIO :: IO a -> SysfsGpioT m a

MonadThrow m => MonadThrow (SysfsGpioT m)

Methods

throwM :: Exception e => e -> SysfsGpioT m a

MonadCatch m => MonadCatch (SysfsGpioT m)

Methods

catch :: Exception e => SysfsGpioT m a -> (e -> SysfsGpioT m a) -> SysfsGpioT m a

MonadMask m => MonadMask (SysfsGpioT m)

Methods

mask :: ((forall a. SysfsGpioT m a -> SysfsGpioT m a) -> SysfsGpioT m b) -> SysfsGpioT m b

uninterruptibleMask :: ((forall a. SysfsGpioT m a -> SysfsGpioT m a) -> SysfsGpioT m b) -> SysfsGpioT m b

MonadLogger m => MonadLogger (SysfsGpioT m)

Methods

monadLoggerLog :: ToLogStr msg => Loc -> LogSource -> LogLevel -> msg -> SysfsGpioT m ()

MonadLoggerIO m => MonadLoggerIO (SysfsGpioT m)

Methods

askLoggerIO :: SysfsGpioT m (Loc -> LogSource -> LogLevel -> LogStr -> IO ())

MonadCont m => MonadCont (SysfsGpioT m)

Methods

callCC :: ((a -> SysfsGpioT m b) -> SysfsGpioT m a) -> SysfsGpioT m a

type StT SysfsGpioT a

type StT SysfsGpioT a = a

type StM (SysfsGpioT m) a

type StM (SysfsGpioT m) a = ComposeSt SysfsGpioT m a

Convenient constraint synonyms for MonadSysfs signatures.

type CatchSysfsM m = (Functor m, MonadCatch m, MonadSysfs m)

type ThrowSysfsM m = (Functor m, MonadThrow m, MonadSysfs m)

type ThrowCatchSysfsM m = (Functor m, MonadThrow m, MonadCatch m, MonadSysfs m)

Low-level sysfs GPIO actions.

sysfsIsPresent :: MonadSysfs m => m Bool

Test whether the sysfs GPIO filesystem is available.

availablePins :: ThrowCatchSysfsM m => m [Pin]

Return a list of all pins that are exposed via the sysfs GPIO filesystem. Note that the returned list may omit some pins that are available on the host but which, for various reasons, are not exposed via the sysfs GPIO filesystem.

pinIsExported :: MonadSysfs m => Pin -> m Bool

Test whether the pin is already exported.

exportPin :: CatchSysfsM m => Pin -> m ()

Export the given pin.

Note that, if the pin is already exported, this is not an error; in this situation, the pin remains exported and its state unchanged.

exportPinChecked :: CatchSysfsM m => Pin -> m ()

Export the given pin.

Note that, unlike exportPin, it's an error to call this action to export a pin that's already been exported. This is the standard Linux sysfs GPIO behavior.

unexportPin :: CatchSysfsM m => Pin -> m ()

Unexport the given pin.

Note that, if the pin is already unexported or cannot be unexported, this is not an error. In this situation, the pin remains exported and its state unchanged.

unexportPinChecked :: CatchSysfsM m => Pin -> m ()

Unexport the given pin.

Note that, unlike unexportPin, it is an error to call this action if the pin is not currently exported. This is the standard Linux sysfs GPIO behavior.

pinHasDirection :: ThrowSysfsM m => Pin -> m Bool

Test whether the pin's direction can be set via the sysfs GPIO filesystem. (Some pins have a hard-wired direction, in which case their direction must be determined by some other mechanism, as the direction attribute does not exist for such pins.)

readPinDirection :: ThrowCatchSysfsM m => Pin -> m PinDirection

Read the pin's direction.

It is an error to call this action if the pin has no direction attribute.

writePinDirection :: CatchSysfsM m => Pin -> PinDirection -> m ()

Set the pin's direction.

It is an error to call this action if the pin has no direction attribute.

Note that, in Linux sysfs GPIO, changing a pin's direction to out will also set its physical signal level to low.

NB: in Linux sysfs, if an input pin is cofigured for edge- or level-triggered reads, it's an error to set its direction to out. However, this action will handle that case gracefully by setting the pin's edge attribute to none before setting the pin's direction to out.

writePinDirectionWithValue :: CatchSysfsM m => Pin -> PinValue -> m ()

Pins whose direction can be set may be configured for output by writing a PinValue to their direction attribute, such that the given value will be driven on the pin as soon as it's configured for output. This enables glitch-free output configuration, assuming the pin is currently configured for input, or some kind of tri-stated or floating high-impedance mode.

It is an error to call this action if the pin has no direction attribute.

NB: for some unfathomable reason, writing high or low to a pin's direction attribute sets its physical signal level; i.e., it ignores the value of the pin's active_low attribute. Contrast this behavior with the behavior of writing to the pin's value attribute, which respects the value of the pin's active_low attribute and sets the pin's logical signal level.

Rather than slavishly following the Linux sysfs GPIO spec, we choose to be consistent by taking into account the pin's active level when writing the direction attribute. In other words, the PinValue argument to this action is the logical signal level that will be set on the pin. If you're using this action to program directly to the Linux sysfs GPIO interface and expecting things to behave as they do with raw sysfs GPIO operations, keep this in mind!

readPinValue :: ThrowCatchSysfsM m => Pin -> m PinValue

Read the pin's signal level.

Note that this action never blocks, regardless of the pin's edge attribute setting.

pollPinValue :: ThrowCatchSysfsM m => Pin -> m PinValue

A blocking version of readPinValue. The current thread will block until an event occurs on the pin as specified by the pin's current edge attribute setting.

If the pin has no edge attribute, then this action's behavior is undefined. (Most likely, it will block indefinitely.)

pollPinValueTimeout :: ThrowCatchSysfsM m => Pin -> Int -> m (Maybe PinValue)

Same as pollPinValue, except that a timeout value, specified in microseconds, is provided. If no event occurs before the timeout expires, this action returns Nothing; otherwise, it returns the pin's value wrapped in a Just.

If the timeout value is negative, this action behaves just like pollPinValue.

When specifying a timeout value, be careful not to exceed maxBound.

If the pin has no edge attribute, then this action's behavior is undefined. (Most likely, it will time out after the specified delay and return Nothing.)

NB: the curent implementation of this action limits the timeout precision to 1 millisecond, rather than 1 microsecond as the timeout parameter implies.

writePinValue :: CatchSysfsM m => Pin -> PinValue -> m ()

Set the pin's signal level.

It is an error to call this action if the pin is configured as an input pin.

pinHasEdge :: ThrowSysfsM m => Pin -> m Bool

Test whether the pin has an edge attribute, i.e., whether it can be configured for edge- or level-triggered interrupts.

readPinEdge :: ThrowCatchSysfsM m => Pin -> m SysfsEdge

Read the pin's edge attribute.

It is an error to call this action when the pin has no edge attribute.

writePinEdge :: CatchSysfsM m => Pin -> SysfsEdge -> m ()

Write the pin's edge attribute.

It is an error to call this action when the pin has no edge attribute, or when the pin is configured for output.

readPinActiveLow :: ThrowCatchSysfsM m => Pin -> m Bool

Read the pin's active_low attribute.

writePinActiveLow :: CatchSysfsM m => Pin -> Bool -> m ()

Write the pin's active_low attribute.