| Copyright | (c) 2009–2014 Bas van Dijk |
|---|---|
| License | BSD3 (see the file LICENSE) |
| Maintainer | Bas van Dijk <v.dijk.bas@gmail.com> |
| Safe Haskell | Trustworthy |
| Language | Haskell98 |
System.USB.Initialization
Contents
Description
This module provides functionality for initializing the usb library.
Documentation
Abstract type representing a USB session.
The concept of individual sessions allows your program to use multiple threads that can independently use this library without interfering with eachother.
Sessions are created and initialized by newCtx and are automatically closed
when they are garbage collected.
The only functions that receive a Ctx are hasCapability, setDebug and
getDevices.
Create and initialize a new USB context.
This function may throw USBExceptions.
Note that the internal libusb event handling can return errors. These errors
occur in the thread that is executing the event handling loop. newCtx will
print these errors to stderr. If you need to handle the errors yourself (for
example log them in an application specific way) please use newCtx'.
newCtx' :: (USBException -> IO ()) -> IO Ctx Source #
Like newCtx but enables you to specify the way errors should be handled
that occur while handling libusb events.
Logging
setDebug :: Ctx -> Verbosity -> IO () Source #
Set message verbosity.
The default level is PrintNothing. This means no messages are ever
printed. If you choose to increase the message verbosity level you must ensure
that your application does not close the stdout/stderr file descriptors.
You are advised to set the debug level to PrintWarnings. Libusb is
conservative with its message logging. Most of the time it will only log
messages that explain error conditions and other oddities. This will help you
debug your software.
The LIBUSB_DEBUG environment variable overrules the debug level set by this function. The message verbosity is fixed to the value in the environment variable if it is defined.
If libusb was compiled without any message logging, this function does nothing:
you'll never get any messages.
If libusb was compiled with verbose debug message logging, this function does
nothing: you'll always get messages from all levels.
Message verbosity
Constructors
| PrintNothing | No messages are ever printed by the library. |
| PrintErrors | Error messages are printed to |
| PrintWarnings | Warning and error messages are printed to |
| PrintInfo | Informational messages are printed to |
| PrintDebug | Debug and informational messages are printed to
|