libusb 批传输的使用方法
概述
libusb是开发与USB外围设备通讯应用程序的好帮手，其API精益且功能强大，完备内容可以查看接口文档和库提供的examples示例程序。
自己使用较多的是USB批量传输类型，在此记录下有关批量传输通讯需要的一些步骤。代码适用于存在批量传输端点的USB设备。
数据结构
- 查找设备的标识
struct bulkusbid
{
unsigned short vid;
unsigned short pid;
};
- 一些必须参数
struct bulkusbdev
{
libusb_device_handle* handle;
uint8_t endpoint_in;
uint8_t endpoint_out;
uint8_t bus;
uint8_t addr;
int nb_ifaces;
};
初始化和退出
int bulkusb_init()
{
return libusb_init(NULL);
}
void bulkusb_exit()
{
libusb_exit(NULL);
}
查找设备
同一产品多个设备它们的pid、vid都是一样的，这里获取这个id下的所有设备以备选择。
int bulkusb_get_list(struct bulkusbdev dev_list[], int dev_max_cnt, struct bulkusbid id_list[], unsigned int id_cnt)
{
int dev_cnt = 0;
struct libusb_device_descriptor desc;
libusb_device** devs;
ssize_t cnt;
int r, i;
unsigned int j;
cnt = libusb_get_device_list(NULL, &devs);
if (cnt < 0)
return (int)cnt;
for (i = 0; devs[i]; ++i)
{
if (dev_cnt >= dev_max_cnt)
{
break;
}
r = libusb_get_device_descriptor(devs[i], &desc);
if (r < 0)
{
fprintf(stderr, "failed to get device descriptor");
return r;
}
for (j = 0; j < id_cnt; j++)
{
if (id_list[j].vid == desc.idVendor &&
id_list[j].pid == desc.idProduct)
{
dev_list[dev_cnt].bus = libusb_get_bus_number(devs[i]);
dev_list[dev_cnt].addr = libusb_get_device_address(devs[i]);
dev_cnt++;
}
}
}
libusb_free_device_list(devs, 1);
return dev_cnt;
}
打开设备
这部分代码主要有以下作用：
- 获取批量读写所需的必须参数
句柄、输入端点、输出端点； - 清除端点的暂停标志并重新；
- 声明接口，这些接口关闭时要释放；
- 重新初始化设备；
这里获取端点需要注意的几点是：
- 只查找第一个设备配置描述符；
- 只查找厂商自定义类型接口或者CDC类型接口；
- 只使用找到的第一个输入输出端点；
- 如果已知输入输出端点，也可以直接写定它们的值，不使用查找的方法；
int bulkusb_open(struct bulkusbdev* bdev)
{
libusb_device** devs;
ssize_t cnt;
int r, i;
cnt = libusb_get_device_list(NULL, &devs);
if (cnt < 0)
{
printf("\n\nlibusb error: %s\n", libusb_strerror((enum libusb_error)cnt));
return (int)cnt;
}
libusb_device* dev = NULL;
libusb_device_handle* handle = NULL;
for (i = 0; devs[i]; ++i)
{
dev = devs[i];
if (bdev->bus == libusb_get_bus_number(devs[i])
&& bdev->addr == libusb_get_device_address(devs[i]))
{
//获得句柄
if (1)
{
r = libusb_open(dev, &handle);
if (LIBUSB_SUCCESS != r)
{
libusb_free_device_list(devs, 1);
printf("\n\nlibusb error: %s\n", libusb_strerror((enum libusb_error)r));
return r;
}
bdev->handle = handle;//赋值
}
//获得通讯端点并声明内核接口
if (1)
{
int i, j, k;
struct libusb_config_descriptor* conf_desc;
const struct libusb_endpoint_descriptor* endpoint;
uint8_t endpoint_in = 0, endpoint_out = 0; // default IN and OUT endpoints
int iface, nb_ifaces;
uint8_t interfaceClass;
libusb_get_config_descriptor(dev, 0, &conf_desc);//uint8_t config_index = 0;
nb_ifaces = conf_desc->bNumInterfaces;
bdev->nb_ifaces = nb_ifaces;//赋值
for (i = 0; i < nb_ifaces; i++) {
for (j = 0; j < conf_desc->interface[i].num_altsetting; j++) {
//只获取接口类别为：厂商自定义类（0xFF）和CDC数据类（0xA）
interfaceClass = conf_desc->interface[i].altsetting[j].bInterfaceClass;
if (interfaceClass != 0xFF && interfaceClass != 0x0A){
continue;
}
for (k = 0; k < conf_desc->interface[i].altsetting[j].bNumEndpoints; k++) {
struct libusb_ss_endpoint_companion_descriptor* ep_comp = NULL;
endpoint = &conf_desc->interface[i].altsetting[j].endpoint[k];
// Use the first bulk IN/OUT endpoints as default for testing
if ((endpoint->bmAttributes & LIBUSB_TRANSFER_TYPE_MASK) & (LIBUSB_TRANSFER_TYPE_BULK)) {//只获取批量传输端点
if (endpoint->bEndpointAddress & LIBUSB_ENDPOINT_IN) {
if (!endpoint_in)
{
endpoint_in = endpoint->bEndpointAddress;
bdev->endpoint_in = endpoint_in;//赋值
libusb_clear_halt(handle, bdev->endpoint_in);//清除暂停标志
}
}
else {
if (!endpoint_out)
{
endpoint_out = endpoint->bEndpointAddress;
bdev->endpoint_out = endpoint_out;//赋值
libusb_clear_halt(handle, bdev->endpoint_out);
}
}
}
}
}
}
libusb_free_config_descriptor(conf_desc);
libusb_set_auto_detach_kernel_driver(handle, 1);
for (iface = 0; iface < nb_ifaces; iface++)
{
r = libusb_claim_interface(handle, iface);
if (r != LIBUSB_SUCCESS) {
printf(" Failed.\n");
}
}
}
}
}
libusb_free_device_list(devs, 1);
if (bdev->endpoint_in == 0 || bdev->endpoint_out == 0)
{
printf("* Failed:endpoint_in or endpoint_out is NULL!\n");
return -99;
}
//重新初始化
libusb_reset_device(bdev->handle);
return 0;
}
关闭设备
int bulkusb_close(struct bulkusbdev* bdev)
{
if (bdev->handle)
{
int iface;
for (iface = 0; iface < bdev->nb_ifaces; iface++) {
printf("Releasing interface %d...\n", iface);
libusb_release_interface(bdev->handle, iface);
}
libusb_close(bdev->handle);
}
return 0;
}
批量写
int bulkusb_write(struct bulkusbdev* dev, void* buffer, int len, int ms)
{
int size, errcode;
libusb_device_handle* handle = dev->handle;
uint8_t endpoint_out = dev->endpoint_out;
errcode = libusb_bulk_transfer(handle, endpoint_out, buffer, len, &size, ms);
if (errcode<0)
{
printf("write: %s\n", libusb_strerror((enum libusb_error)errcode));
return -1;
}
return size;
}
批量读
int bulkusb_read(struct bulkusbdev* dev, void* buffer, size_t len, int ms)
{
int size, errcode;
libusb_device_handle* handle = dev->handle;
uint8_t endpoint_in = dev->endpoint_in;
errcode = libusb_bulk_transfer(handle, endpoint_in, buffer, len, &size, ms);
if (errcode < 0)
{
printf("read: %s\n", libusb_strerror((enum libusb_error)errcode));
return -1;
}
return size;
}
步骤执行顺序
char buf[8] = { 0 };
struct bulkusbdev* dev = NULL;
struct bulkusbdev devs[2] = { 0 };
struct bulkusbid ids[1] = {
{
.vid = 0x1234,
.pid = 0x1122
}
};
bulkusb_init();
bulkusb_get_list(devs, 2, ids, 1);
dev = &devs[0];
bulkusb_open(dev);
bulkusb_write(dev, buf, 8, 1000);
bulkusb_read(dev, buf, 8, 1000);
bulkusb_close(dev);
bulkusb_exit();
