Maintainer | Bas van Dijk <v.dijk.bas@gmail.com> |
---|
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 setDebug
and getDevices
.
Create and initialize a new USB context.
This function may throw USBException
s.
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
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 |