USB driver for Linux user space using kernel hid gadget sub system

usb_driver.c

/*
 * =====================================================================================
 *
 *       Filename:  usb_driver.c
 *
 *    Description:  
 *
 *        Version:  1.0
 *        Created:  12/31/2020 02:37:05 PM
 *       Revision:  none
 *       Compiler:  gcc
 *
 *         Author:  Yair Gadelov (yg), yair.gadelov@gmail.com
 *        Company:  Israel
 *
 * =====================================================================================
 */
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

#include "usb_driver.h"
#define DEVICE_NAME "/dev/hidg0"

static char keyb_report_desc[] = {

	0x05, 0x01,        // Usage Page (Generic Desktop Ctrls)
	0x09, 0x06,        // Usage (Keyboard)
	0xA1, 0x01,        // Collection (Application)
	0x05, 0x07,        //   Usage Page (Kbrd/Keypad)
	0x19, 0xE0,        //   Usage Minimum (0xE0)
	0x29, 0xE7,        //   Usage Maximum (0xE7)
	0x15, 0x00,        //   Logical Minimum (0)
	0x25, 0x01,        //   Logical Maximum (1)
	0x75, 0x01,        //   Report Size (1)
	0x95, 0x08,        //   Report Count (8)
	0x81, 0x02,        //   Input (Data,Var,Abs,No Wrap,Linear,Preferred State,No Null Position)
	0x95, 0x01,        //   Report Count (1)
	0x75, 0x08,        //   Report Size (8)
	0x81, 0x03,        //   Input (Const,Var,Abs,No Wrap,Linear,Preferred State,No Null Position)
	0x95, 0x05,        //   Report Count (5)
	0x75, 0x01,        //   Report Size (1)
	0x05, 0x08,        //   Usage Page (LEDs)
	0x19, 0x01,        //   Usage Minimum (Num Lock)
	0x29, 0x05,        //   Usage Maximum (Kana)
	0x91, 0x02,        //   Output (Data,Var,Abs,No Wrap,Linear,Preferred State,No Null Position,Non-volatile)
	0x95, 0x01,        //   Report Count (1)
	0x75, 0x03,        //   Report Size (3)
	0x91, 0x03,        //   Output (Const,Var,Abs,No Wrap,Linear,Preferred State,No Null Position,Non-volatile)
	0x95, 0x06,        //   Report Count (6)
	0x75, 0x08,        //   Report Size (8)
	0x15, 0x00,        //   Logical Minimum (0)
	0x25, 0x65,        //   Logical Maximum (101)
	0x05, 0x07,        //   Usage Page (Kbrd/Keypad)
	0x19, 0x00,        //   Usage Minimum (0x00)
	0x29, 0x65,        //   Usage Maximum (0x65)
	0x81, 0x00,        //   Input (Data,Array,Abs,No Wrap,Linear,Preferred State,No Null Position)
	0xC0,              // End Collection

	// 63 bytes
};

static int mkpath(char *p) {
	char *path = strdup(p);
	char  *save_path = path;
	char *sep1;
	char *sep2=0;
	do {
		int idx = (sep2-path)<0 ? 0 : sep2-path;
		sep1 = strchr(path + idx , '/');	
		sep2 = strchr(sep1+1, '/');
		if (sep2) {
			path[sep2-path]=0;
		}
		if(mkdir(path, 0777) && errno != EEXIST)
			return -1;
		if (sep2) {
			path[sep2-path]='/';
		}
	} while (sep2);

	free(save_path);
	return 0;

}
static int mkfile (char *filename,char *value) {
	int fd = open (filename,O_RDWR);
	if (fd<0)
		return -1;
	int n = write (fd,value,strlen(value));
	close(fd);
	return n;
}
static int mkfile1 (char *filename,char *value,int len) {
	int fd = open (filename,O_RDWR);
	if (fd<0)
		return -1;
	int n = write (fd,value,len);
	close(fd);
	return n;
}
static int usbhid_setup() {
	FILE *pipe;
	char line[128];
	int linenr;

	pipe = popen("modprobe usb_f_mass_storage;modprobe configfs;modprobe libcomposite;", "r");
	if (pipe == NULL) {  /* check for errors */
	//	perror(argv[0]); /* report error message */
		return -1;        /* return with exit code indicating error */
	}
	/* Read script output from the pipe line by line */
	linenr = 1;
	while (fgets(line, 128, pipe) != NULL) {
		printf("Script output line %d: %s", linenr, line);
		+linenr;
	}		
	pclose(pipe); 


	
	mkpath ("/sys/kernel/config/usb_gadget/g1");
	mkfile ("/sys/kernel/config/usb_gadget/g1/bMaxPacketSize0","64");
	mkfile ("/sys/kernel/config/usb_gadget/g1/bcdUSB","0x200");
	mkfile ("/sys/kernel/config/usb_gadget/g1/idVendor","0x13bb");
	mkfile ("/sys/kernel/config/usb_gadget/g1/idProduct","0x7801");

	mkpath ("/sys/kernel/config/usb_gadget/g1/configs/c1.1/strings/0x409");	
	mkfile ("/sys/kernel/config/usb_gadget/g1/strings/c1.1/MaxPower","120");	
	mkfile ("/sys/kernel/config/usb_gadget/g1/configs/c1.1/strings/0x409/configuration","Test Device");


	
	mkpath ("/sys/kernel/config/usb_gadget/g1/strings/0x409");
	mkfile ("/sys/kernel/config/usb_gadget/g1/strings/0x409/manufacturer","Test Device INC ...");
	mkfile ("/sys/kernel/config/usb_gadget/g1/strings/0x409/product","BISx");
	mkfile ("/sys/kernel/config/usb_gadget/g1/strings/0x409/serialnumber","0");



	
	// mass storage
	mkpath ("/sys/kernel/config/usb_gadget/g1/functions/mass_storage.ms0/lun.0");
	mkfile ("/sys/kernel/config/usb_gadget/g1/functions/mass_storage.ms0/lun.0/file","/home/root/fat.fs");
	mkfile ("/sys/kernel/config/usb_gadget/g1/functions/mass_storage.ms0/lun.0/removable","1");
	symlink("/sys/kernel/config/usb_gadget/g1/functions/mass_storage.ms0", "/sys/kernel/config/usb_gadget/g1/configs/c1.1/mass_storage.ms0");// functions/mass_storage.ms0->configs/c1.1

	// hid
	mkpath ("/sys/kernel/config/usb_gadget/g1/functions/hid.0");
	mkfile ("/sys/kernel/config/usb_gadget/g1/functions/hid.0/protocol","1");
	mkfile ("/sys/kernel/config/usb_gadget/g1/functions/hid.0/subclass","1");
	mkfile ("/sys/kernel/config/usb_gadget/g1/functions/hid.0/report_length","8");
	mkfile1 ("/sys/kernel/config/usb_gadget/g1/functions/hid.0/report_desc",keyb_report_desc,sizeof (keyb_report_desc));

	symlink("/sys/kernel/config/usb_gadget/g1/functions/hid.0", "/sys/kernel/config/usb_gadget/g1/configs/c1.1/hid.0");// functions/hid.0->configs/c1.1



	mkfile ("/sys/kernel/config/usb_gadget/g1/UDC","49000000.usb-otg");

}

int usbhid_diable() {
	mkfile ("/sys/kernel/config/usb_gadget/g1/UDC","");

}

int usbhid_enable() {
	mkfile ("/sys/kernel/config/usb_gadget/g1/UDC","49000000.usb-otg");

}
int usbhid_open() {
	int fd;
	usbhid_setup();
	usleep(500000);
	if ((fd = open(DEVICE_NAME, O_RDWR, 0666)) == -1) {
		perror(DEVICE_NAME);
		return -1;
	}
	return fd;

}

int usbhid_read(int fd,char *buffer,int length) {
	int n = read(fd, buffer,length);
	return n;
}

int usbhid_write(int fd,char *buffer,int length) {
	int n = write(fd, buffer,length);
	return n;
}

#define CONFIG_SETUP_USB_DRIVER
#ifdef CONFIG_SETUP_USB_DRIVER
int main(int argc, char *argv[] ) {
	char report[8];
	int fd  = usbhid_open()
	if (fd  <0)
		exit(1);
	// send message from device (usually embbeded linux device) to host (it can be a PC for example)
	for (int i=0;i<10;i++) {
		report[0]=0x12;
		report[1]=0x34;
		report[2]=0x56;
		report[3]=0x78;
		report[4]=0x9a;
		report[5]=0xbc;
		report[6]=0xde;
		report[7]=0xf0;
		usbhid_write (fd, report, 8);
		memset(report, 0x0, sizeof(report));write(fd, report, 8);
		sleep(1);
	}
	
}
#endif

A simple example of how to uses HID gadget subsystem in Embbeed Linux device. The device has to include a USB OTG HW to be a USB device. This example uses HID devices to send communication data between HOST and embedded Linux devices. See this post for further details.

new link to the post https://yairgadelov.me/linux-gadget-device./