玩转USB系列:Linux下使用C语言和libusb开发USB HID
实验环境
- ubuntu 16.04 LTS 64-bit
- gcc,vim
- STM32做下位机
开发步骤
安装libusb
sudo apt-get install libusb-1.0-0
注意:我在网上找到了多个安装教程写的安装命令和我的不一样:
- sudo apt-get install libusb-dev
- sudo apt-get install libusb-1.0-0-dev
这些命令安装的libusb我没有探索过,但有一点我知道,也是特容易踩坑的地方:
不同的libusb引用的头文件和函数还有编译时加的库名有细微的区别!!坑死我了
而好多教程都是上来就列代码,这就导致我们在看文章的时候觉得挺好,但是在自己机器上就是找不到函数或者头文件或者编译不过去等等…
本文章下面都以sudo apt-get install libusb-1.0-0为例子
试试好用否
我们来先试一试列出usb设备:
#include <unistd.h>
#include <stdio.h>
#include <libusb-1.0/libusb.h>
static void print_devs(libusb_device **devs)
{
libusb_device *dev;
int i = 0;
while ((dev = devs[i++]) != NULL) {
struct libusb_device_descriptor desc;
int r = libusb_get_device_descriptor(dev, &desc);
if (r < 0) {
fprintf(stderr, "failed to get device descriptor");
return;
}
printf("%04x:%04x (bus %d, device %d)\n",
desc.idVendor, desc.idProduct,
libusb_get_bus_number(dev), libusb_get_device_address(dev));
}
}
int main()
{
int r;
ssize_t cnt;
libusb_device **devs; //devices
r=libusb_init(NULL); //init 初始化libusb
if(r<0) {
printf("failed to init libusb\n");
return 1;
}
cnt = libusb_get_device_list(NULL,&devs); //获取设备列表
if (cnt < 0) {
printf("failed to get device list\n");
return 1;
}
print_devs(devs);
return 0;
}
保存,然后编译:注意!!编译的时候加上库名,就像这样
gcc hid_test_show.c -o hid -lusb-1.0
编译后执行:
看起来是不是和lsusb命令很像?
这一步正确了,就证明libusb已经安装可以使用了,往下!
我们来与HID设备通讯!
我的STM32信息:
interface 0
END POINT 0x01: OUT
END POINT 0x82: IN
包大小:64 byte
完成功能:PC机向STM32写入2个字节(查询命令)
STM32返回5个字节:[0]:数据长度(这里应该为4)[0]-[4]:一个double的电压值的内存形式
上代码:
#include <unistd.h>
#include <stdio.h>
#include <libusb-1.0/libusb.h>
static void print_devs(libusb_device **devs)
{
libusb_device *dev;
int i = 0;
while ((dev = devs[i++]) != NULL) {
struct libusb_device_descriptor desc;
int r = libusb_get_device_descriptor(dev, &desc);
if (r < 0) {
fprintf(stderr, "failed to get device descriptor");
return;
}
printf("%04x:%04x (bus %d, device %d)\n",
desc.idVendor, desc.idProduct,
libusb_get_bus_number(dev), libusb_get_device_address(dev));
}
}
int main()
{
int r;
ssize_t cnt;
libusb_device_handle *dev_handle; //a device handle
libusb_device **devs; //devices
//libusb_context **ctx=NULL;
r=libusb_init(NULL); //init 初始化libusb
if(r<0) {
printf("failed to init libusb\n");
return 1;
}
cnt = libusb_get_device_list(NULL,&devs); //获取设备列表
if (cnt < 0) {
printf("failed to get device list\n");
return 1;
}
//print_devs(devs);
dev_handle = libusb_open_device_with_vid_pid(NULL, 0x0483, 0xa010);
if(dev_handle == NULL){
printf("Cannot open device\n");
return 1;
}else
printf("Device Opened\n");
libusb_free_device_list(devs, 1); //free the list, unref the devices in it
if(libusb_kernel_driver_active(dev_handle, 0) == 1) { //find out if kernel driver is attached
printf("Kernel Driver Active\n");
if(libusb_detach_kernel_driver(dev_handle, 0) == 0) //detach it
printf("Kernel Driver Detached!\n");
}
r = libusb_claim_interface(dev_handle, 0); //claim interface 0 (the first) of device (mine had jsut 1)
if(r < 0) {
printf("Cannot Claim Interface\n");
return 1;
}
printf("Claimed Interface\n");
sleep(1);
unsigned char data[2];
union f_to_char{
char chr[4];
float ft0;
}temp_union;
unsigned char tmp_char[64];
data[0]=0x02;data[1]=0x64;
int actual; //used to find out how many bytes were written
while(1){
r = libusb_interrupt_transfer(dev_handle, (0x01 | LIBUSB_ENDPOINT_OUT), data, 2, &actual, 0); //my device's out endpoint was 1, found with trial- the device had 2 endpoints: 2 and 129
if(r == 0 && actual == 2) //we wrote the 2 bytes successfully
printf("Writing Successful\n");
else
printf("Write Error\n");
r = libusb_interrupt_transfer(dev_handle, (0x82 | LIBUSB_ENDPOINT_IN),tmp_char,64,&actual, 1000);//pay attion
if(r == 0 && actual == 64) //we read the 64 bytes successfully
printf("Read Successful\n");
else
printf("Read Error\n");
//printf("%i,%i\n",r,actual);
temp_union.chr[0]=tmp_char[1];
temp_union.chr[1]=tmp_char[2];
temp_union.chr[2]=tmp_char[3];
temp_union.chr[3]=tmp_char[4];
printf("The volt is %f mV\n",temp_union.ft0);
usleep(1000*500);
printf("%s","\033[1H\033[2J");//clear display
}
r = libusb_release_interface(dev_handle, 0); //release the claimed interface
if(r!=0) {
printf("Cannot Release Interface\n");
return 1;
}
printf("Released Interface\n");
libusb_close(dev_handle); //close the device we opened
libusb_exit(NULL); //needs to be called to end the
return 0;
}
探索、学习与注意:
1.&ctx是个什么鬼
(代码中调用libusb接口函数需要先建立上下文环境,其中结构体struct libusb_context代表一段libusb的会话,官方文档中有对这个结构的说明。
libusb_init()表示开启会话,libusb_exit()表示结束会话。通俗的理解就是struct libusb_context* ctx中的ctx代表一把钥匙,libusb_init(&ctx)表示开启,libusb_exit(null)表示锁上。)
这段解释来自网上,但是,我对其存疑!
因为,有另一篇帖子代码上所有的ctx位置全部给的NULL
我当前代码中全部ctx位置全部给的NULL,目前没发现问题。
2.print_devs(devs)->print_devs(&devs);
执行就显示这个(这个就是偶然写错了发现的~)
3.操作端口这类程序加上sudo !
dev_handle = libusb_open_device_with_vid_pid(ctx, 0x0483, 0xa010);
if(dev_handle == NULL){
printf("Cannot open device\n");
return 1;
}else
printf("Device Opened\n");
找不到设备的时候先检查sudo加没加,不一定是设备不正常
不加sudo会Cannot open device,加上才打的开
4.libusb_interrupt_transfer这个函数是write和read一体的!
我当初找了半天读写函数在哪里,害!
5.找不到函数报错的时候别急查网上,把头文件打开搜索一下更管用!
之前已经说过了,libusb的函数有一些细微区别,还是自己看所安装libusb的文档或者头文件吧~
6.终端清屏指令
printf("%s","\033[1H\033[2J");//clear display