带有本地库的安卓系统--接口是CDC的USB设备--不能在本地库中使用fd

Question 1

我试图让一个安卓平板电脑与一个USB设备（STM32 Nucleo）进行通信。我开发了一个草图，可在 github :

the mobile application is developped with Xamarin and VS Studio. It acts as usb host

the STM32 Nucleo application is developped with STMCube and uses it's USB stack to act as a CDC device.

I developped a small master/slave protocol to echange "register" id/value. The device is the slave.

我设法使用Android.hardware.usb API使其工作。但我必须使用本地C共享对象库进行通信，因为它在其他平台上使用，这就是 我现在有麻烦了 . 我使用swig嵌入了这个库，并使用VS Studio构建它。我尝试了两种方法来使库与设备进行通信。

From the Android side get permission and fd and pass it to the library that does standard read/write opérations.

From the Android do the same as above, but also pass with fd the endpoints numbers that uses the linux usbdevice_fs API to call bulk transfers; more o less like presented at that question .

这两个方法都失败了，并返回一个关于不存在的fd的错误。我检查了fd和enpoints的值，它们和安卓系统是一样的。我启动了安卓的usb设备监视器，我找不到创建的fd。我无法使用任何安卓的shell，比如termux来列出进程/proc树。但我仍然可以在安卓系统中使用它们。

我从社区里查到，把fd传给本地库是正确的方法。我不知道现在该怎么做，是否有更多的权限可以请求？

Below is how I retrieve the fd :

               _devHandle.usbdev = _devHandle.usbManager.DeviceList[name];
            // Ask for permission to access the created device
            if (!_devHandle.usbManager.HasPermission(_devHandle.usbdev))
                PendingIntent pi = PendingIntent.GetBroadcast((ContextWrapper)_context, 0, new Intent(ACTION_USB_PERMISSION), 0);
                _devHandle.usbManager.RequestPermission(_devHandle.usbdev, pi);
                /* We check the permission was given
                if (!_devHandle.usbManager.HasPermission(_devHandle.usbdev))
                    // Loose !
                    Log.Debug("pandavcom", "FAILED : did not have persmission to open device" + _devHandle.usbdev.DeviceName);
                    return;
            // Now open the port, with  the USB Manager : we get the fd/enpoints and pass it to library, no more
            _devHandle.connection = _devHandle.usbManager.OpenDevice(_devHandle.usbdev);
            if (_devHandle.connection != null)
                if (OpenInterface(_devHandle.usbdev, _devHandle.connection, ref _devHandle.usbIface, ref _devHandle.ep_in, ref _devHandle.ep_out) == 0)
                    _devHandle.fd = _devHandle.connection.FileDescriptor;
                    Log.Debug("pandavcom", "opened device endpoint" + _devHandle.usbdev.DeviceName + "with descriptor: " + _devHandle.fd);
                    Log.Debug("pandavcom", "FAILED : open device endpoint" + _devHandle.usbdev.DeviceName);

Question 2


          
           所以我把它弄好了，感谢libusb邮件列表中的那些人。
事实上，疯狂电阻libusb只能向设备发送数据。
现在有了正式的libusb，就有了一种方法，这还是最近的。
          
          
           So the process is :
          
          
           
            用安卓系统获取设备权限和文件描述符
           
          
          
           
            将文件描述符传递给你的本地代码，并执行这一步以
initliaze libusb on the fd :
           
            libusb_context *ctx;
 enum libusb_error rc;
 rc = libusb_set_option(&ctx, LIBUSB_OPTION_WEAK_AUTHORITY, NULL);
 if (rc != LIBUSB_SUCCESS) {
     __android_log_print(ANDROID_LOG_ERROR, TAG,"libusb_init failed: %d\n", ret);
     return -1;
 ret = libusb_init(&ctx);
 if (ret < 0) {
     __android_log_print(ANDROID_LOG_INFO, TAG,
                         "libusb_init failed: %d\n", ret);
     return 1;
 libusb_device_handle *devh = NULL;
 ret = libusb_wrap_sys_device(NULL, (intptr_t)FD, &devh);
 if (ret < 0) {
     __android_log_print(ANDROID_LOG_INFO, TAG,
                         "libusb_wrap_sys_device failed: %d\n", ret);
     return 2;
 else if (devh == NULL) {
     __android_log_print(ANDROID_LOG_INFO, TAG,
                         "libusb_wrap_sys_device returned invalid handle\n");
     return 3;
(FD = FileDescriptor from Android.USBManager)