Copyright	(c) 2016, Drew Hess
License	BSD3
Maintainer	Drew Hess <src@drewhess.com>
Stability	experimental
Portability	non-portable
Safe Haskell	Trustworthy
Language	Haskell2010

System.GPIO.Linux.Sysfs.Monad

Contents

MonadSysfs class
GPIO via sysfs
Low-level sysfs GPIO actions.

Description

Monad type classes and instances for Linux sysfs GPIO operations.

Synopsis

MonadSysfs class

class Monad m => MonadSysfs m where Source

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

Methods

doesDirectoryExist :: FilePath -> m Bool Source

Equivalent to doesDirectoryExist.

doesFileExist :: FilePath -> m Bool Source

Equivalent to doesFileExist.

getDirectoryContents :: FilePath -> m [FilePath] Source

Equivalent to getDirectoryContents.

readFile :: FilePath -> m ByteString Source

Equivalent to readFile.

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

Equivalent to writeFile.

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

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 Source

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 (CatchT m) Source
MonadSysfs m => MonadSysfs (ListT m) Source
MonadSysfs m => MonadSysfs (MaybeT m) Source
MonadSysfs m => MonadSysfs (IdentityT m) Source
(MonadIO m, MonadThrow m) => MonadSysfs (SysfsIOT m) Source
(Functor m, MonadThrow m) => MonadSysfs (SysfsMockT m) Source
MonadSysfs m => MonadSysfs (ContT r m) Source
MonadSysfs m => MonadSysfs (ReaderT r m) Source
MonadSysfs m => MonadSysfs (StateT s m) Source
MonadSysfs m => MonadSysfs (StateT s m) Source
MonadSysfs m => MonadSysfs (ExceptT e m) Source
(MonadSysfs m, Monoid w) => MonadSysfs (WriterT w m) Source
(MonadSysfs m, Monoid w) => MonadSysfs (WriterT w m) Source
(MonadSysfs m, Monoid w) => MonadSysfs (RWST r w s m) Source
(MonadSysfs m, Monoid w) => MonadSysfs (RWST r w s m) Source

GPIO via `sysfs`

newtype PinDescriptor Source

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 Source
Ord PinDescriptor Source
Show PinDescriptor Source
(Functor m, MonadCatch m, MonadMask m, MonadThrow m, MonadSysfs m) => MonadGpio PinDescriptor (SysfsGpioT m) Source

newtype SysfsGpioT m a Source

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 Source
MonadRWS r w s m => MonadRWS r w s (SysfsGpioT m) Source
MonadError e m => MonadError e (SysfsGpioT m) Source
MonadReader r m => MonadReader r (SysfsGpioT m) Source
MonadState s m => MonadState s (SysfsGpioT m) Source
MonadWriter w m => MonadWriter w (SysfsGpioT m) Source
(Functor m, MonadCatch m, MonadMask m, MonadThrow m, MonadSysfs m) => MonadGpio PinDescriptor (SysfsGpioT m) Source
Monad m => Monad (SysfsGpioT m) Source
Functor m => Functor (SysfsGpioT m) Source
MonadFix m => MonadFix (SysfsGpioT m) Source
Applicative m => Applicative (SysfsGpioT m) Source
Alternative m => Alternative (SysfsGpioT m) Source
MonadPlus m => MonadPlus (SysfsGpioT m) Source
MonadThrow m => MonadThrow (SysfsGpioT m) Source
MonadCatch m => MonadCatch (SysfsGpioT m) Source
MonadMask m => MonadMask (SysfsGpioT m) Source
MonadIO m => MonadIO (SysfsGpioT m) Source
MonadCont m => MonadCont (SysfsGpioT m) Source

Low-level `sysfs` GPIO actions.

sysfsIsPresent :: MonadSysfs m => m Bool Source

Test whether the sysfs GPIO filesystem is available.

availablePins :: (MonadSysfs m, MonadThrow m, MonadCatch m) => m [Pin] Source

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 Source

Test whether the pin is already exported.

exportPin :: (MonadSysfs m, MonadCatch m) => Pin -> m () Source

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 :: (MonadCatch m, MonadSysfs m) => Pin -> m () Source

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 :: (MonadSysfs m, MonadCatch m) => Pin -> m () Source

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 :: (MonadSysfs m, MonadCatch m) => Pin -> m () Source

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 :: (MonadSysfs m, MonadThrow m) => Pin -> m Bool Source

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 :: (MonadSysfs m, MonadThrow m, MonadCatch m) => Pin -> m PinDirection Source

Read the pin's direction.

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

writePinDirection :: (MonadSysfs m, MonadCatch m) => Pin -> PinDirection -> m () Source

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 :: (MonadSysfs m, MonadCatch m) => Pin -> PinValue -> m () Source

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 :: (MonadSysfs m, MonadThrow m, MonadCatch m) => Pin -> m PinValue Source

Read the pin's signal level.

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

pollPinValue :: (Functor m, MonadSysfs m, MonadThrow m, MonadCatch m) => Pin -> m PinValue Source

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 :: (Functor m, MonadSysfs m, MonadThrow m, MonadCatch m) => Pin -> Int -> m (Maybe PinValue) Source

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 :: (MonadSysfs m, MonadCatch m) => Pin -> PinValue -> m () Source

Set the pin's signal level.

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

pinHasEdge :: (MonadSysfs m, MonadThrow m) => Pin -> m Bool Source

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

readPinEdge :: (MonadSysfs m, MonadThrow m, MonadCatch m) => Pin -> m SysfsEdge Source

Read the pin's edge attribute.

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

writePinEdge :: (MonadSysfs m, MonadCatch m) => Pin -> SysfsEdge -> m () Source

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 :: (MonadSysfs m, MonadThrow m, MonadCatch m) => Pin -> m Bool Source