A cross-platform user library to access USB devices
Functions
Synchronous device I/O

This page documents libusb's synchronous (blocking) API for USB device I/O. More...

Functions

int libusb_control_transfer (libusb_device_handle *dev_handle, uint8_t bmRequestType, uint8_t bRequest, uint16_t wValue, uint16_t wIndex, unsigned char *data, uint16_t wLength, unsigned int timeout)
 Perform a USB control transfer. More...
 
int libusb_bulk_transfer (struct libusb_device_handle *dev_handle, unsigned char endpoint, unsigned char *data, int length, int *transferred, unsigned int timeout)
 Perform a USB bulk transfer. More...
 
int libusb_interrupt_transfer (struct libusb_device_handle *dev_handle, unsigned char endpoint, unsigned char *data, int length, int *transferred, unsigned int timeout)
 Perform a USB interrupt transfer. More...
 

Detailed Description

This page documents libusb's synchronous (blocking) API for USB device I/O.

This interface is easy to use but has some limitations. More advanced users may wish to consider using the asynchronous I/O API instead.

Function Documentation

int libusb_control_transfer ( libusb_device_handle dev_handle,
uint8_t  bmRequestType,
uint8_t  bRequest,
uint16_t  wValue,
uint16_t  wIndex,
unsigned char *  data,
uint16_t  wLength,
unsigned int  timeout 
)

Perform a USB control transfer.

The direction of the transfer is inferred from the bmRequestType field of the setup packet.

The wValue, wIndex and wLength fields values should be given in host-endian byte order.

Parameters
dev_handlea handle for the device to communicate with
bmRequestTypethe request type field for the setup packet
bRequestthe request field for the setup packet
wValuethe value field for the setup packet
wIndexthe index field for the setup packet
dataa suitably-sized data buffer for either input or output (depending on direction bits within bmRequestType)
wLengththe length field for the setup packet. The data buffer should be at least this size.
timeouttimeout (in millseconds) that this function should wait before giving up due to no response being received. For an unlimited timeout, use value 0.
Returns
on success, the number of bytes actually transferred
LIBUSB_ERROR_TIMEOUT if the transfer timed out
LIBUSB_ERROR_PIPE if the control request was not supported by the device
LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
another LIBUSB_ERROR code on other failures
int libusb_bulk_transfer ( struct libusb_device_handle dev_handle,
unsigned char  endpoint,
unsigned char *  data,
int  length,
int *  transferred,
unsigned int  timeout 
)

Perform a USB bulk transfer.

The direction of the transfer is inferred from the direction bits of the endpoint address.

For bulk reads, the length field indicates the maximum length of data you are expecting to receive. If less data arrives than expected, this function will return that data, so be sure to check the transferred output parameter.

You should also check the transferred parameter for bulk writes. Not all of the data may have been written.

Also check transferred when dealing with a timeout error code. libusb may have to split your transfer into a number of chunks to satisfy underlying O/S requirements, meaning that the timeout may expire after the first few chunks have completed. libusb is careful not to lose any data that may have been transferred; do not assume that timeout conditions indicate a complete lack of I/O.

Parameters
dev_handlea handle for the device to communicate with
endpointthe address of a valid endpoint to communicate with
dataa suitably-sized data buffer for either input or output (depending on endpoint)
lengthfor bulk writes, the number of bytes from data to be sent. for bulk reads, the maximum number of bytes to receive into the data buffer.
transferredoutput location for the number of bytes actually transferred.
timeouttimeout (in millseconds) that this function should wait before giving up due to no response being received. For an unlimited timeout, use value 0.
Returns
0 on success (and populates transferred)
LIBUSB_ERROR_TIMEOUT if the transfer timed out (and populates transferred)
LIBUSB_ERROR_PIPE if the endpoint halted
LIBUSB_ERROR_OVERFLOW if the device offered more data, see Packets and overflows
LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
another LIBUSB_ERROR code on other failures
int libusb_interrupt_transfer ( struct libusb_device_handle dev_handle,
unsigned char  endpoint,
unsigned char *  data,
int  length,
int *  transferred,
unsigned int  timeout 
)

Perform a USB interrupt transfer.

The direction of the transfer is inferred from the direction bits of the endpoint address.

For interrupt reads, the length field indicates the maximum length of data you are expecting to receive. If less data arrives than expected, this function will return that data, so be sure to check the transferred output parameter.

You should also check the transferred parameter for interrupt writes. Not all of the data may have been written.

Also check transferred when dealing with a timeout error code. libusb may have to split your transfer into a number of chunks to satisfy underlying O/S requirements, meaning that the timeout may expire after the first few chunks have completed. libusb is careful not to lose any data that may have been transferred; do not assume that timeout conditions indicate a complete lack of I/O.

The default endpoint bInterval value is used as the polling interval.

Parameters
dev_handlea handle for the device to communicate with
endpointthe address of a valid endpoint to communicate with
dataa suitably-sized data buffer for either input or output (depending on endpoint)
lengthfor bulk writes, the number of bytes from data to be sent. for bulk reads, the maximum number of bytes to receive into the data buffer.
transferredoutput location for the number of bytes actually transferred.
timeouttimeout (in millseconds) that this function should wait before giving up due to no response being received. For an unlimited timeout, use value 0.
Returns
0 on success (and populates transferred)
LIBUSB_ERROR_TIMEOUT if the transfer timed out
LIBUSB_ERROR_PIPE if the endpoint halted
LIBUSB_ERROR_OVERFLOW if the device offered more data, see Packets and overflows
LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
another LIBUSB_ERROR code on other error