HID: Documentation for hidraw

      HIDRAW - Raw Access to USB and Bluetooth Human Interface Devices

     ==================================================================

The hidraw driver provides a raw interface to USB and Bluetooth Human

Interface Devices (HIDs).  It differs from hiddev in that reports sent and

received are not parsed by the HID parser, but are sent to and received from

the device unmodified.

Hidraw should be used if the userspace application knows exactly how to

communicate with the hardware device, and is able to construct the HID

reports manually.  This is often the case when making userspace drivers for

custom HID devices.

Hidraw is also useful for communicating with non-conformant HID devices

which send and receive data in a way that is inconsistent with their report

descriptors.  Because hiddev parses reports which are sent and received

through it, checking them against the device's report descriptor, such

communication with these non-conformant devices is impossible using hiddev.

Hidraw is the only alternative, short of writing a custom kernel driver, for

these non-conformant devices.

A benefit of hidraw is that its use by userspace applications is independent

of the underlying hardware type.  Currently, Hidraw is implemented for USB

and Bluetooth.  In the future, as new hardware bus types are developed which

use the HID specification, hidraw will be expanded to add support for these

new bus types.

Hidraw uses a dynamic major number, meaning that udev should be relied on to

create hidraw device nodes.  Udev will typically create the device nodes

directly under /dev (eg: /dev/hidraw0).  As this location is distribution-

and udev rule-dependent, applications should use libudev to locate hidraw

devices attached to the system.  There is a tutorial on libudev with a

working example at:

	http://www.signal11.us/oss/udev/

The HIDRAW API

---------------

read()

-------

read() will read a queued report received from the HID device. On USB

devices, the reports read using read() are the reports sent from the device

on the INTERRUPT IN endpoint.  By default, read() will block until there is

a report available to be read.  read() can be made non-blocking, by passing

the O_NONBLOCK flag to open(), or by setting the O_NONBLOCK flag using

fcntl().

On a device which uses numbered reports, the first byte of the returned data

will be the report number; the report data follows, beginning in the second

byte.  For devices which do not use numbered reports, the report data

will begin at the first byte.

write()

--------

The write() function will write a report to the device. For USB devices, if

the device has an INTERRUPT OUT endpoint, the report will be sent on that

endpoint. If it does not, the report will be sent over the control endpoint,

using a SET_REPORT transfer.

The first byte of the buffer passed to write() should be set to the report

number.  If the device does not use numbered reports, the first byte should

be set to 0. The report data itself should begin at the second byte.

ioctl()

--------

Hidraw supports the following ioctls:

HIDIOCGRDESCSIZE: Get Report Descriptor Size

This ioctl will get the size of the device's report descriptor.

HIDIOCGRDESC: Get Report Descriptor

This ioctl returns the device's report descriptor using a

hidraw_report_descriptor struct.  Make sure to set the size field of the

hidraw_report_descriptor struct to the size returned from HIDIOCGRDESCSIZE.

HIDIOCGRAWINFO: Get Raw Info

This ioctl will return a hidraw_devinfo struct containing the bus type, the

vendor ID (VID), and product ID (PID) of the device. The bus type can be one

of:

	BUS_USB

	BUS_HIL

	BUS_BLUETOOTH

	BUS_VIRTUAL

which are defined in linux/input.h.

HIDIOCGRAWNAME(len): Get Raw Name

This ioctl returns a string containing the vendor and product strings of

the device.  The returned string is Unicode, UTF-8 encoded.

HIDIOCGRAWPHYS(len): Get Physical Address

This ioctl returns a string representing the physical address of the device.

For USB devices, the string contains the physical path to the device (the

USB controller, hubs, ports, etc).  For Bluetooth devices, the string

contains the hardware (MAC) address of the device.

HIDIOCSFEATURE(len): Send a Feature Report

This ioctl will send a feature report to the device.  Per the HID

specification, feature reports are always sent using the control endpoint.

Set the first byte of the supplied buffer to the report number.  For devices

which do not use numbered reports, set the first byte to 0. The report data

begins in the second byte. Make sure to set len accordingly, to one more

than the length of the report (to account for the report number).

HIDIOCGFEATURE(len): Get a Feature Report

This ioctl will request a feature report from the device using the control

endpoint.  The first byte of the supplied buffer should be set to the report

number of the requested report.  For devices which do not use numbered

reports, set the first byte to 0.  The report will be returned starting at

the first byte of the buffer (ie: the report number is not returned).

Example

---------

In samples/, find hid-example.c, which shows examples of read(), write(),

and all the ioctls for hidraw.  The code may be used by anyone for any

purpose, and can serve as a starting point for developing applications using

hidraw.

Document by:

	Alan Ott <alan@signal11.us>, Signal 11 Software

	  Build an example of how to dynamically add the hello

	  command to the kdb shell.

config SAMPLE_HIDRAW

	tristate "Build simple hidraw example"

	depends on HIDRAW

	help

	  Build an example of how to use hidraw from userspace.

endif # SAMPLES

# Makefile for Linux samples code

obj-$(CONFIG_SAMPLES)	+= kobject/ kprobes/ tracepoints/ trace_events/ \

			   hw_breakpoint/ kfifo/ kdb/

			   hw_breakpoint/ kfifo/ kdb/ hidraw/

# kbuild trick to avoid linker error. Can be omitted if a module is built.

obj- := dummy.o

# List of programs to build

hostprogs-y := hid-example

# Tell kbuild to always build the programs

always := $(hostprogs-y)

/*

 * Hidraw Userspace Example

 *

 * Copyright (c) 2010 Alan Ott <alan@signal11.us>

 * Copyright (c) 2010 Signal 11 Software

 *

 * The code may be used by anyone for any purpose,

 * and can serve as a starting point for developing

 * applications using hidraw.

 */

/* Linux */

#include <linux/types.h>

#include <linux/input.h>

#include <linux/hidraw.h>

/* Unix */

#include <sys/ioctl.h>

#include <sys/types.h>

#include <sys/stat.h>

#include <fcntl.h>

#include <unistd.h>

/* C */

#include <stdio.h>

#include <string.h>

#include <stdlib.h>

#include <errno.h>

const char *bus_str(int bus);

int main(int argc, char **argv)

{

	int fd;

	int i, res, desc_size = 0;

	char buf[256];

	struct hidraw_report_descriptor rpt_desc;

	struct hidraw_devinfo info;

	/* Open the Device with non-blocking reads. In real life,

	   don't use a hard coded path; use libudev instead. */

	fd = open("/dev/hidraw0", O_RDWR|O_NONBLOCK);

	if (fd < 0) {

		perror("Unable to open device");

		return 1;

	}

	memset(&rpt_desc, 0x0, sizeof(rpt_desc));

	memset(&info, 0x0, sizeof(info));

	memset(buf, 0x0, sizeof(buf));

	/* Get Report Descriptor Size */

	res = ioctl(fd, HIDIOCGRDESCSIZE, &desc_size);

	if (res < 0)

		perror("HIDIOCGRDESCSIZE");

	else

		printf("Report Descriptor Size: %d\n", desc_size);

	/* Get Report Descriptor */

	rpt_desc.size = desc_size;

	res = ioctl(fd, HIDIOCGRDESC, &rpt_desc);

	if (res < 0) {

		perror("HIDIOCGRDESC");

	} else {

		printf("Report Descriptor:\n");

		for (i = 0; i < rpt_desc.size; i++)

			printf("%hhx ", rpt_desc.value[i]);

		puts("\n");

	}

	/* Get Raw Name */

	res = ioctl(fd, HIDIOCGRAWNAME(256), buf);

	if (res < 0)

		perror("HIDIOCGRAWNAME");

	else

		printf("Raw Name: %s\n", buf);

	/* Get Physical Location */

	res = ioctl(fd, HIDIOCGRAWPHYS(256), buf);

	if (res < 0)

		perror("HIDIOCGRAWPHYS");

	else

		printf("Raw Phys: %s\n", buf);

	/* Get Raw Info */

	res = ioctl(fd, HIDIOCGRAWINFO, &info);

	if (res < 0) {

		perror("HIDIOCGRAWINFO");

	} else {

		printf("Raw Info:\n");

		printf("\tbustype: %d (%s)\n",

			info.bustype, bus_str(info.bustype));

		printf("\tvendor: 0x%04hx\n", info.vendor);

		printf("\tproduct: 0x%04hx\n", info.product);

	}

	/* Set Feature */

	buf[0] = 0x9; /* Report Number */

	buf[1] = 0xff;

	buf[2] = 0xff;

	buf[3] = 0xff;

	res = ioctl(fd, HIDIOCSFEATURE(4), buf);

	if (res < 0)

		perror("HIDIOCSFEATURE");

	else

		printf("ioctl HIDIOCGFEATURE returned: %d\n", res);

	/* Get Feature */

	buf[0] = 0x9; /* Report Number */

	res = ioctl(fd, HIDIOCGFEATURE(256), buf);

	if (res < 0) {

		perror("HIDIOCGFEATURE");

	} else {

		printf("ioctl HIDIOCGFEATURE returned: %d\n", res);

		printf("Report data (not containing the report number):\n\t");

		for (i = 0; i < res; i++)

			printf("%hhx ", buf[i]);

		puts("\n");

	}

	/* Send a Report to the Device */

	buf[0] = 0x1; /* Report Number */

	buf[1] = 0x77;

	res = write(fd, buf, 2);

	if (res < 0) {

		printf("Error: %d\n", errno);

		perror("write");

	} else {

		printf("write() wrote %d bytes\n", res);

	}

	/* Get a report from the device */

	res = read(fd, buf, 16);

	if (res < 0) {

		perror("read");

	} else {

		printf("read() read %d bytes:\n\t", res);

		for (i = 0; i < res; i++)

			printf("%hhx ", buf[i]);

		puts("\n");

	}

	close(fd);

	return 0;

}

const char *

bus_str(int bus)

{

	switch (bus) {

	case BUS_USB:

		return "USB";

		break;

	case BUS_HIL:

		return "HIL";

		break;

	case BUS_BLUETOOTH:

		return "Bluetooth";

		break;

	case BUS_VIRTUAL:

		return "Virtual";

		break;

	default:

		return "Other";

		break;

	}

}