libusb1.0学习

来源：互联网发布：syslog端口编辑：程序博客网时间：2024/05/15 00:03

作者：AAA20090987

转自：http://blog.csdn.net/small_qch/article/details/6625111

接学习一，学习二主要是看例程

ok，现在最简单的想法看看有多少信息包含在你的设备里，程序代码如下

[cpp] view plaincopyprint?

#include <iostream>
#include <libusb.h>
using namespace std;
void printdev(libusb_device *dev); //prototype of the function
int main() {
libusb_device **devs; //pointer to pointer of device, used to retrieve a list of devices
libusb_context *ctx = NULL; //a libusb session
int r; //for return values
ssize_t cnt; //holding number of devices in list
r = libusb_init(&ctx); //initialize a library session
if(r < 0) {
cout<<"Init Error "<<r<<endl; //there was an error
return 1;
}
libusb_set_debug(ctx, 3); //set verbosity level to 3, as suggested in the documentation
cnt = libusb_get_device_list(ctx, &devs); //get the list of devices
if(cnt < 0) {
cout<<"Get Device Error"<<endl; //there was an error
}
cout<<cnt<<" Devices in list."<<endl; //print total number of usb device
ssize_t i; //for iterating through the list
for(i = 0; i < cnt; i++) {
printdev(devs[i]); //print specs of this device
}
libusb_free_device_list(devs, 1); //free the list, unref the devices in it
libusb_exit(ctx); //close the session
return 0;
}
void printdev(libusb_device *dev) {
libusb_device_descriptor desc;
int r = libusb_get_device_descriptor(dev, &desc);
if (r < 0) {
cout<<"failed to get device descriptor"<<endl;
return;
}
cout<<"Number of possible configurations: "<<(int)desc.bNumConfigurations<<" ";
cout<<"Device Class: "<<(int)desc.bDeviceClass<<" ";
cout<<"VendorID: "<<desc.idVendor<<" ";
cout<<"ProductID: "<<desc.idProduct<<endl;
libusb_config_descriptor *config;
libusb_get_config_descriptor(dev, 0, &config);
cout<<"Interfaces: "<<(int)config->bNumInterfaces<<" ||| ";
const libusb_interface *inter;
const libusb_interface_descriptor *interdesc;
const libusb_endpoint_descriptor *epdesc;
for(int i=0; i<(int)config->bNumInterfaces; i++) {
inter = &config->interface[i];
cout<<"Number of alternate settings: "<<inter->num_altsetting<<" | ";
for(int j=0; j<inter->num_altsetting; j++) {
interdesc = &inter->altsetting[j];
cout<<"Interface Number: "<<(int)interdesc->bInterfaceNumber<<" | ";
cout<<"Number of endpoints: "<<(int)interdesc->bNumEndpoints<<" | ";
for(int k=0; k<(int)interdesc->bNumEndpoints; k++) {
epdesc = &interdesc->endpoint[k];
cout<<"Descriptor Type: "<<(int)epdesc->bDescriptorType<<" | ";
cout<<"EP Address: "<<(int)epdesc->bEndpointAddress<<" | ";
}
}
}
cout<<endl<<endl<<endl;
libusb_free_config_descriptor(config);
}

写完之后，编译看看会出现什么。首先运行程序并检查设备，然后连上我自己的设备在执行程序。会发现有新的内容出现，可以根据vendor id和product id发现这正是我自己连上打开的设备。
注意：发现设备（调用libusb_get_device_list()）会返回新的内存分配的设备队列。当你完成这个队列的使用后必须释放他。
Libusb同样需要知道当一切完成时清除队列的内容；设备的本身。
为处理这些问题，libusb提供了两个单独的条目：
一个释放队列本身的函数
一个针对设备内部的参考计数系统
新的设备由libusb_get_device_list()函数展示，都拥有一个参考计数1。你可以使用libubs_ref_device()和libusb_unref_device()增加或减少参考计数。当一个设备的参考计数为0时，该设备就被销毁
通过以上的信息，打开设备的基本流程可以视为如下步骤：
1. 使用libusb_get_device_list()发现设备；
2. 选择你想操作的设备，调用libusb_open();
3. 在设备队列中unref所有的设备；
4. 释放已经发现的设备队列；
这个次序是十分重要的，在尝试打开设备之前，你不能够unreference设备，因此unreference操作有可能导致设备的销毁。
为了方便起见，libusb_free_device_list()函数包含一个参数，在释放队列本身前，该参数能够选择性地在队列中unreference所有设备。这包含了以上的步骤3和步骤4。
如果还有需要，可以去libusb1’s API（http://libusb.sourceforge.net/api-1.0/index.html）文档参考你需要的函数。
好了，现在你可以找到你需要的设备了。现在是打开设备，请求并且执行一个简单的I/O。如果你知道vendor ID和prouct ID，使用libusb_open_device_with_vid_pid。
另外需要注意的，如果内核（你的OS）已经连接到这个设备，你将无法请求到它。在这种情况下，你需要调用libusb_detach_kernel_drive来从内核中检测设备。如果你想知道内核是否可用的，使用libusb_kernel_drive_active,如果返回值为1，对于你的设备内核可以加载驱动。
批量传输
为了在你的设备上使用批量传输，你应该获得为你的USB设备获得一个设备句柄，并且你应该知道使用哪个端点（从之前设备说明获得）。
关于语法上的信息参考这里（http://libusb.sourceforge.net/api-1.0/group__syncio.html#gab8ae853ab492c22d707241dc26c8a805）
这里有个简单的例子包含所有我提到的相关部分：

[cpp] view plaincopyprint?

#include <iostream>
#include <libusb.h>
using namespace std;
int main() {
libusb_device **devs; //pointer to pointer of device, used to retrieve a list of devices
libusb_device_handle *dev_handle; //a device handle
libusb_context *ctx = NULL; //a libusb session
int r; //for return values
ssize_t cnt; //holding number of devices in list
r = libusb_init(&ctx); //initialize the library for the session we just declared
if(r < 0) {
cout<<"Init Error "<<r<<endl; //there was an error
return 1;
}
libusb_set_debug(ctx, 3); //set verbosity level to 3, as suggested in the documentation
cnt = libusb_get_device_list(ctx, &devs); //get the list of devices
if(cnt < 0) {
cout<<"Get Device Error"<<endl; //there was an error
return 1;
}
cout<<cnt<<" Devices in list."<<endl;
dev_handle = libusb_open_device_with_vid_pid(ctx, 5118, 7424); //these are vendorID and productID I found for my usb device
if(dev_handle == NULL)
cout<<"Cannot open device"<<endl;
else
cout<<"Device Opened"<<endl;
libusb_free_device_list(devs, 1); //free the list, unref the devices in it
unsigned char *data = new unsigned char[4]; //data to write
data[0]='a';data[1]='b';data[2]='c';data[3]='d'; //some dummy values
int actual; //used to find out how many bytes were written
if(libusb_kernel_driver_active(dev_handle, 0) == 1) { //find out if kernel driver is attached
cout<<"Kernel Driver Active"<<endl;
if(libusb_detach_kernel_driver(dev_handle, 0) == 0) //detach it
cout<<"Kernel Driver Detached!"<<endl;
}
r = libusb_claim_interface(dev_handle, 0); //claim interface 0 (the first) of device (mine had jsut 1)
if(r < 0) {
cout<<"Cannot Claim Interface"<<endl;
return 1;
}
cout<<"Claimed Interface"<<endl;
cout<<"Data->"<<data<<"<-"<<endl; //just to see the data we want to write : abcd
cout<<"Writing Data..."<<endl;
r = libusb_bulk_transfer(dev_handle, (2 | LIBUSB_ENDPOINT_OUT), data, 4, &actual, 0); //my device's out endpoint was 2, found with trial- the device had 2 endpoints: 2 and 129
if(r == 0 && actual == 4) //we wrote the 4 bytes successfully
cout<<"Writing Successful!"<<endl;
else
cout<<"Write Error"<<endl;
r = libusb_release_interface(dev_handle, 0); //release the claimed interface
if(r!=0) {
cout<<"Cannot Release Interface"<<endl;
return 1;
}
cout<<"Released Interface"<<endl;
libusb_close(dev_handle); //close the device we opened
libusb_exit(ctx); //needs to be called to end the
delete[] data; //delete the allocated memory for data
return 0;
}

结尾：这个教程对于这个话题来说是十分简单的介绍，需要时间需联系同步传输，然后移动是异步的，这还有很多需要学习。
希望这些对你的初学有帮助。

原文连接：http://blog.cnnbboy.com/?p=313

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