Libusb庫的使用
轉自:http://blog.sina.com.cn/s/blog_4a5b632801009upv.html
使用libusb之前你的linux系統必須裝有usb文件系統，這裏還介紹了使用hiddev設備文件來訪問設備，目的在於不僅可以比較出usb的易用性，還提供了一個轉化成libusb驅動的案例。
任何驅動第一步首先是尋找到要操作的設備，我們先來看看HID驅動是怎樣尋找到設備的。我們假設尋找設備的函數Device_Find(注：代碼只是爲了方便解說，不保證代碼的健全)
int Device_Find()
{
char dir_str[100];
char hiddev[100];
DIR dir;
memset (dir_str, 0 , sizeof(dir_str));
memset (hiddev, 0 , sizeof(hiddev));
dir=opendir("/dev/usb/hid");
if(dir){
sprintf(dir_str,"/dev/usb/hid/");
closedir(dir);
}else{
sprintf(dir_str,"/dev/usb/");
}
for(i = 0; i < DEVICE_MINOR; i++) {
sprintf(hiddev, "%shiddev%d", dir_str,i);
fd = open(hiddev, O_RDWR);
if(fd > 0) {
ioctl(fd, HIDIOCGDEVINFO, &info);
if(info.vendor== VENDOR_ID && info.product== PRODUCT_ID) {
device_num++;
}
close(fd);
}
}
return device_num;
}
我們再來看libusb是如何來尋找和初始化設備
int Device_Find()
{
struct usb_bus *busses;
int device_num = 0;
device_num = 0;
usb_init();
usb_find_busses();
usb_find_devices();
busses = usb_get_busses();
struct usb_bus *bus;
for (bus = busses; bus; bus = bus->next) {
struct usb_device *dev;
for (dev = bus->devices; dev; dev = dev->next) {
if(dev->descriptor.idVendor==VENDOR_ID&& dev->descriptor.idProduct == PRODUCT_ID) {
device_num++;
}
}
}
return device_num;
}
注：在新版本的libusb中，usb_get_busses就可以不用了，這個函數是返回系統上的usb總線鏈表句柄
這裏我們直接用usb_busses變量，這個變量在usb.h中被定義爲外部變量
所以可以直接寫成這樣：
struct usb_bus *bus;
for (bus = usb_busses; bus; bus = bus->next) {
struct usb_device *dev;
for (dev = bus->devices; dev; dev = dev->next) {
}
}
假設我們定義的打開設備的函數名是device_open,
int Device_Open()
{
int handle;
handle = open(“hiddev0”, O_RDONLY);
}
int Device_Open()
{
struct usb_device* udev;
usb_dev_handle* device_handle;
device_handle = usb_open(udev);
}
假設我們的設備使用控制傳輸方式，至於批處理傳輸和中斷傳輸限於篇幅這裏不介紹
我們這裏定義三個函數，Device_Write, Device_Read, Device_Report
Device_Report 功能發送接收函數
Device_Write 功能寫數據
Device_Read 功能讀數據
Device_Write和Device_Read調用Device_Report發送寫的信息和讀的信息，開發者根據發送的命令協議來設計，我們這裏只簡單實現發送數據的函數。
假設我們要給設備發送72字節的數據，頭8個字節是報告頭，是我們定義的和設備相關的規則，後64位是數據。
HID驅動的實現(這裏只是用代碼來有助理解，代碼是僞代碼)
int Device_Report(int fd, unsigned char *buffer72)
{
int ret;
int index;
unsigned char send_data[72];
unsigned char recv_data[72];
struct hiddev_usage_ref uref;
struct hiddev_report_info rinfo;
ret = ioctl(fd, HIDIOCINITREPORT, 0);
if( ret !=0) {
return NOT_OPENED_DEVICE;
}
for(index = 0; index < 72; index++) {
uref.report_type = HID_REPORT_TYPE_FEATURE;
uref.report_id = HID_REPORT_ID_FIRST;
uref.usage_index = index;
uref.field_index = 0;
uref.value = send_data[index];
ioctl(fd, HIDIOCGUCODE, &uref);
ret=ioctl(fd, HIDIOCSUSAGE, &uref);
if(ret != 0 ){
return UNKNOWN_ERROR;
}
}
rinfo.report_type = HID_REPORT_TYPE_FEATURE;
rinfo.report_id = HID_REPORT_ID_FIRST;
rinfo.num_fields = 1;
ret=ioctl(fd, HIDIOCSREPORT, &rinfo);
if(ret != 0) {
return WRITE_REPORT;
}
ret = ioctl(fd, HIDIOCINITREPORT, 0);
for(index = 0; index < 72; index++) {
uref.report_type = HID_REPORT_TYPE_FEATURE;
uref.report_id = HID_REPORT_ID_FIRST;
uref.usage_index = index;
uref.field_index = 0;
ioctl(fd, HIDIOCGUCODE, &uref);
ret = ioctl(fd, HIDIOCGUSAGE, &uref);
if(ret != 0 ) {
return UNKNOWN_ERROR;
}
recv_data[index] = uref.value;
}
memcpy(buffer72, recv_data, 72);
return SUCCESS;
}
libusb驅動的實現
int Device_Report(int fd, unsigned char *buffer72)
{
usb_dev_handle* Device_handle;
unsigned char send_data[72];
unsigned char recv_data[72];
int send_len;
int recv_len;
memset(send_data, 0 , sizeof(send_data));
memset(recv_data, 0 , sizeof(recv_data));
Device_handle = (usb_dev_handle*)(g_list[fd].device_handle);
if (Device_handle == NULL) {
return NOT_OPENED_DEVICE;
}
usb_claim_interface(Device_handle, 0);
send_len = usb_control_msg(Device_handle,
USB_ENDPOINT_OUT + USB_TYPE_CLASS + USB_RECIP_INTERFACE,
HID_REPORT_SET,
0x300,
0,
send_data, 72, USB_TIMEOUT);
if (send_len < 0) {
return WRITE_REPORT;
}
if (send_len != 72) {
return send_len;
}
recv_len = usb_control_msg(Device_handle,
USB_ENDPOINT_IN + USB_TYPE_CLASS + USB_RECIP_INTERFACE,
HID_REPORT_GET,
0x300,
0,
recv_data, 72, USB_TIMEOUT);
if (recv_len < 0) {
printf("failed to retrieve report from USB device!/n");
return READ_REPORT;
}
if (recv_len != 72) {
return recv_len;
}
usb_release_interface(RY2_handle, 0);
memcpy(buffer72, recv_data, 72);
return SUCCESS;
}
假設我們定義的關閉設備的函數名是Device_Close()
int Device_Close()
{
int handle;
handle = open(“hiddev0”, O_RDONLY);
close( handle );
}
int Device_Close()
{
struct usb_device* udev;
usb_dev_handle* device_handle;
device_handle = usb_open(udev);
usb_close(device_handle);
}
前面我們看了些主要的libusb函數的使用，這裏我們把前面的內容歸納下：
一般的驅動應該都包含如下接口：
Device_Find();
Device_Open();
Device_Write();
Device_Read();
Device_Close();
具體代碼如下：
#include <usb.h>typedef struct{ struct usb_device* udev; usb_dev_handle* device_handle; } device_descript;#define USB_TIMEOUT 10000#define VENDOR_ID 0xffff #define PRODUCT_ID 0xffff#define DEVICE_MINOR 16int g_num;device_descript g_list[ DEVICE_MINOR ];int Device_Find(){ struct usb_bus *bus; struct usb_device *dev; g_num = 0; usb_find_busses(); usb_find_devices(); for (bus = usb_busses; bus; bus = bus->next) { for (dev = bus->devices; dev; dev = dev->next) {if(dev->descriptor.idVendor==VENDOR_ID&& dev->descriptor.idProduct == PRODUCT_ID) { if (g_num < DEVICE_MINOR) { g_list[g_num].udev = dev; g_num ++; } } } } return g_num;}int Device_Open(){ if(g_list[g_num].udev != NULL) {
g_list[g_num].device_handle = usb_open(g_list[g_num].udev);}}int DeviceWite(int handle){ }int DeviceOpen(int handle){ }void Device_close(int handle){ }