usb-0.6: Communicate with USB devices

MaintainerBas van Dijk <v.dijk.bas@gmail.com>

System.USB.Initialization

Description

This module provides functionality for initializing the usb library.

Synopsis

Documentation

data Ctx Source

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 setDebug and getDevices.

Instances

newCtx :: IO CtxSource

Create and initialize a new USB context.

This function may throw USBExceptions.

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.

data Verbosity Source

Message verbosity

Constructors

PrintNothing

No messages are ever printed by the library

PrintErrors

Error messages are printed to stderr

PrintWarnings

Warning and error messages are printed to stderr

PrintInfo

Informational messages are printed to stdout, warning and error messages are printed to stderr