Debian libusb usb_bulk_read（）无法正常工作

Question

我正在尝试通过USB与基于GTM-5210F12的指纹扫描仪进行通信。操作系统是Debian9。为此，基于libusb编写了简单的代码。好像，WRITE操作没问题（因为usb_bulk_write返回正确的写入字节大小），但是当我尝试读取响应时-它始终为0，并且读取缓冲区为空。怎么了？

此扫描仪具有适用于Windows和Android的SDK，但不适用于Linux。某些搜索向我提供了一些信息，即Scanner Android SDK使用了基于很少修改的libusb版本的标准Android SDK功能。

#define VENDOR  0x2009
#define PRODUCT 0x7638
....
usb_init();
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)
                && (dev->descriptor.idProduct == PRODUCT)) {
            // calc params
            int endpointW =
                    dev->config->interface[0].altsetting[0].endpoint[1].bEndpointAddress;
            int endpointWPacketSize =
                    dev->config->interface[0].altsetting[0].endpoint[1].wMaxPacketSize;
            int endpointR =
                    dev->config->interface[0].altsetting[0].endpoint[0].bEndpointAddress;
            int endpointRPacketSize =
                    dev->config->interface[0].altsetting[0].endpoint[0].wMaxPacketSize;
            int interfaceId =
                    dev->config->interface[0].altsetting[0].bInterfaceNumber; // 0
            int configurationValue = dev->config->bConfigurationValue;

            // print params
            printf("Endpoint OUT number: %x", endpointW);
            printf("Endpoint OUT packet size: %i", endpointWPacketSize);
            printf("Endpoint IN number: %x", endpointR);
            printf("Endpoint IN packet size: %i", endpointRPacketSize);

            // try to open device
            usb_dev_handle* handler = usb_open(dev);
            if (handler != nullptr) {
                usb_detach_kernel_driver_np(handler, interfaceId);
                usb_set_configuration(handler, configurationValue);
            }

            // try to obtain interface
            usb_claim_interface(handler, interfaceId);

            // try to write data
            uint8_t wBuffer[endpointWPacketSize];
            memset(wBuffer, 0, sizeof(wBuffer));

            // start bytes
            wBuffer[0] = 0x55;
            wBuffer[1] = 0xaa;
            // device addr
            wBuffer[2] = 0x01;
            wBuffer[3] = 0x00;
            // param
            wBuffer[4] = 0x00;
            wBuffer[5] = 0x00;
            wBuffer[6] = 0x00;
            wBuffer[7] = 0x00;
            // command
            wBuffer[8] = 0x01;
            wBuffer[9] = 0x00;
            // checksum
            wBuffer[10] = 0x01;
            wBuffer[11] = 0x01;

            res = usb_bulk_write(handler, endpointW, (char*) wBuffer,
                    endpointWPacketSize, 200);
            printf("usb_bulk_write() %i", res);

            // try to read data
            uint8_t rBuffer[endpointRPacketSize];
            memset(rBuffer, 0, sizeof(rBuffer));
            res = usb_bulk_read(handler, endpointR, (char*) rBuffer,
                    endpointRPacketSize, 200);
            printf("usb_bulk_read() %i", res);

            // release interface
            usb_release_interface(handler, interfaceId);

            // close usb
            usb_close(handler);
        }
    }
}
...

控制台：

Endpoint OUT number: 2
Endpoint OUT packet size: 64
Endpoint IN number: 81
Endpoint IN packet size: 64
usb_bulk_write() success, 64 bytes written
usb_bulk_read() success, 0 bytes read
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00