Unable to claim USB interface with C + libusb on Mac OS X

问题:

I've got a compound USB + CDC device I built using a PIC32 microcontroller, and I'm trying to connect to the device and send some data to the CDC data interface endpoint from my Mac.

I know the circuit works 100%, as the device registers as both a HID joystick, and I'm able to connect to the device using Zoc terminal, on /dev/tty.usbmodemfa132. I can send commands with Zoc, and see my MCU responding to these commands by blinking some LEDs on the circuit.

I'm running this on Mac OS X Mavericks, but had the same problem with a similar example I gave up on, a few weeks ago on Mountain Lion.

My code looks like follows:

// Includes ----------------------------------------------------------------------------------------------------------- #include  #include  #include  #include  #include   // Defines ------------------------------------------------------------------------------------------------------------ #define VID 0x04d8 #define PID 0x005e #define CDC_DATA_INTERFACE_ID 2  // Function Declarations ---------------------------------------------------------------------------------------------- void print_device(libusb_device *device); void send(libusb_context *usb_context, uint16_t vid, uint16_t pid);  // Function Definitions -----------------------------------------------------------------------------------------------  /**  * main  */ int main(int argc, char **argv) {     libusb_device **usb_devices = NULL;     libusb_context *usb_context = NULL;     ssize_t device_count = 0;     bool debug_enabled = false;     int c;      // Collect command line attributes     while ( (c = getopt(argc, argv, "d")) != -1) {         switch (c) {             case 'd':                 debug_enabled = true;                 break;         }     }      // Initialize USB context     int result = libusb_init(&usb_context);     if(result 

I'm getting the following error output:

libusb: 0.828223 error [darwin_open] USBDeviceOpen: another process has device opened for exclusive access libusb: 0.828241 info [darwin_open] device open for access Device successfully opened Kernel driver doesn't appear to be active libusb: 0.828641 error [darwin_claim_interface] USBInterfaceOpen: another process has device opened for exclusive access Unable to claim interface! libusb: 0.828766 info [event_thread_main] thread exiting 

Is there a way I can release the USB device from the other process, freeing it up so I can claim it?

Is there an alternative way I can connect to /dev/tty.usbmodemfa132 to send and receive data to the CDC interface on the USB device?

An alternative to libusb perhaps?

回答1:

That's right. While libusb seems to be all-powerful in Linux, you cannot use it to connect to a USB CDC interface on Mac OS X because that interface is already claimed by the AppleUSBCDCACM driver.

What you should do is use the standard way that people connect to serial ports. This will be easier because you don't have to worry about endpoints and bulk transfers and such. Here is some example cross-platform C code I wrote for one of our CDC-based products that connects to a COM port to read and write some data (source). It uses the standard functions open, read, and write.

// Uses POSIX functions to send and receive data from a Maestro. // NOTE: You must change the 'const char * device' line below.  #include  #include  #include   #ifdef _WIN32 #define O_NOCTTY 0 #else #include  #endif  // Gets the position of a Maestro channel. // See the "Serial Servo Commands" section of the user's guide. int maestroGetPosition(int fd, unsigned char channel) {   unsigned char command[] = {0x90, channel};   if(write(fd, command, sizeof(command)) == -1)   {     perror("error writing");     return -1;   }    unsigned char response[2];   if(read(fd,response,2) != 2)   {     perror("error reading");     return -1;   }    return response[0] + 256*response[1]; }  // Sets the target of a Maestro channel. // See the "Serial Servo Commands" section of the user's guide. // The units of 'target' are quarter-microseconds. int maestroSetTarget(int fd, unsigned char channel, unsigned short target) {   unsigned char command[] = {0x84, channel, target & 0x7F, target >> 7 & 0x7F};   if (write(fd, command, sizeof(command)) == -1)   {     perror("error writing");     return -1;   }   return 0; }  int main() {   // Open the Maestro's virtual COM port.   const char * device = "\\\\.\\USBSER000";  // Windows, "\\\\.\\COM6" also works   //const char * device = "/dev/ttyACM0";  // Linux   //const char * device = "/dev/cu.usbmodem00034567"; // Mac OS X   int fd = open(device, O_RDWR | O_NOCTTY);   if (fd == -1)   {     perror(device);     return 1;   }  #ifndef _WIN32   struct termios options;   tcgetattr(fd, &options);   options.c_lflag &= ~(ECHO | ECHONL | ICANON | ISIG | IEXTEN);   options.c_oflag &= ~(ONLCR | OCRNL);   tcsetattr(fd, TCSANOW, &options); #endif    int position = maestroGetPosition(fd, 0);   printf("Current position is %d.\n", position);     int target = (position 

回答2:

If you want to use some USB device that is also recognised by the Apple FTDI serial driver, you can first unload the driver:

sudo kextunload -b com.apple.driver.AppleUSBFTDI 

After that you can use it through libusb normally.

For other devices that are recognised as serial devices, you probably need to unload some other driver.

文章来源: Unable to claim USB interface with C + libusb on Mac OS X