How to get device descriptor and configuration descriptor of usb device in Mac?

Question

I have minimum exposure to xcode and I/Okit framework. I have seen device descriptor and configuration descriptor of a usb device in USB prober.

I have written an xcode program using I/O kit framework which gives the usb device name as output, when we give product id and vendor id of that device as input.

/*Take the vendor and product id from console*/

printf("\nEnter the vendor id : ");
scanf("%lx",&usbVendor);

printf("\nEnter the product id :");
scanf("%lx",&usbProduct);


/* Set up a matching dictionary for the class */
matchingDict = IOServiceMatching(kIOUSBDeviceClassName);
if (matchingDict == NULL)
{
    return -1; // fail
}
// Create a CFNumber for the idVendor and set the value in the dictionary
numberRef = CFNumberCreate(kCFAllocatorDefault, kCFNumberSInt32Type, &usbVendor);
CFDictionarySetValue(matchingDict, 
                     CFSTR(kUSBVendorID), 
                     numberRef);
CFRelease(numberRef);

// Create a CFNumber for the idProduct and set the value in the dictionary
numberRef = CFNumberCreate(kCFAllocatorDefault, kCFNumberSInt32Type, &usbProduct);
CFDictionarySetValue(matchingDict, 
                     CFSTR(kUSBProductID), 
                     numberRef);
CFRelease(numberRef);
numberRef = NULL;

/*Get an iterator.*/
kr = IOServiceGetMatchingServices(kIOMasterPortDefault, matchingDict, &iter);
if (kr != KERN_SUCCESS)
{
    return -1;// fail
}

/* iterate */
while ((device = IOIteratorNext(iter)))
{
    /*Display the device names */

    io_name_t       deviceName;
    kr = IORegistryEntryGetName(device, deviceName);
    if (KERN_SUCCESS != kr) {
        deviceName[0] = '\0';
    }


    printf("\ndeviceName:%s",deviceName);

    /*Free the reference taken before continuing to the next item */
    IOObjectRelease(device);
}

/*Release the iterator */
IOObjectRelease(iter);
return 0;

}

I need to modify this, so that on giving vendor and product id of usb device, i will get the device descriptor and configuration descriptor( as shown in USB prober) as output.

Here i just gave an example, code can change but the output must be the descriptor( atleast the device decriptor).

Thanks in advance...

Answer 1

I think u should download the source code of USBProber rather than figure it out by yourself.

All the information presents in the USBProber u could get sooner or later by analyzing the source code.

Here is link to download the source code of IOUSBFamily, with USBProber inside it. http://opensource.apple.com/tarballs/IOUSBFamily/

Answer 2

To get the configuration descriptors you can use code like this:

IOUSBDeviceInterface650** dev = ...;
IOUSBConfigurationDescriptor* configDesc = nullptr;

// Get the configuration descriptor for the first configuration (configuration 0).
kern_return_t kr = (*dev)->GetConfigurationDescriptorPtr(dev, 0, &configDesc);
if (kr != kIOReturnSuccess)
    return an_error;

// Now use configDesc->...

Unfortunately there doesn't seem to be a function to get the device descriptor. There are functions to get some of it:

kr = (*dev)->GetDeviceClass(dev, &desc.bDeviceClass);
kr = (*dev)->GetDeviceSubClass(dev, &desc.bDeviceSubClass);
kr = (*dev)->GetDeviceProtocol(dev, &desc.bDeviceProtocol);
kr = (*dev)->GetDeviceVendor(dev, &desc.idVendor);
kr = (*dev)->GetDeviceProduct(dev, &desc.idProduct);
kr = (*dev)->GetDeviceReleaseNumber(dev, &desc.bcdDevice);
kr = (*dev)->GetNumberOfConfigurations(dev, &desc.bNumConfigurations);

But I don't see a way to get iManufacturer, iProduct, iSerial, bMaxPacketSize0, or bcdUSB.

There is a way around this - instead of using the built-in functions you can just do a control request to get the device descriptor (and configuration descriptors if you like) manually using a control transfer.

The USB 2.0 spec describes how to do this. Basically you:

1. Do a control transfer with bmRequestType = Device | Standard | In, bRequest = USB_GET_DESCRIPTOR_REQUEST, wValue = (USB_DEVICE_DESCRIPTOR_TYPE << 8), wIndex = 0, wLength = 2. That will fail because the descriptor is longer than 2, but it gets you the descriptor header which includes its length.

2. Repeat that request but with the correct length.

3. For configuration descriptors, do a third request with length wTotalLength.

You can do it with one less request since you know the size of the descriptors in advance, but I like to do it like that because then you can wrap it up in a very general getDescriptor() method.

In theory you can do it as simply as this:

IOUSBDeviceDescriptor devDesc;

IOUSBDevRequest request;
request.bmRequestType = USBmakebmRequestType(kUSBIn, kUSBStandard, kUSBDevice);
request.bRequest = kUSBRqGetDescriptor;
request.wValue = kUSBDeviceDesc << 8;
request.wIndex = 0;
request.wLength = sizeof(devDesc); // 18
request.pData = &devDesc;
request.wLenDone = 0;

kern_return_t kr = (*dev)->DeviceRequest(dev, &request);

But for some reason that is giving me a kIOUSBPipeStalled error. Not sure why.

Edit: I forgot the << 8. Now it works. :-)

Answer 3

The header IOKit/usb/USBSpec.h has a documented list of property keys corresponding to values inside the different descriptors. You can use those with IORegistryEntrySearchCFProperty (or similar functions) to get the descriptor values. This way you don't need a device request from an IOUSBDeviceInterface, which is advantageous because:

• the documentation (comments) say that all device requests require and opened USB device and you may not have permission to do that for all devices (it's possible the documentation is wrong, at least for descriptor requests, but I have no guarantee of that and it seems better to follow it anyway)
• device requests can block for an indeterminate amount of time
• the manufacturer, product, and serial number strings (which are referenced by the device descriptor, but are not technically part of it) are not retrieved in this request

Answer 4

For getting device descriptor and configuration decriptor, we can use functions in IOUSBDeviceInterface class

Link: http://developer.apple.com/library/mac/#documentation/Darwin/Reference/IOKit/IOUSBLib_h/Classes/IOUSBDeviceInterface/index.html#//apple_ref/doc/com/intfm/IOUSBDeviceInterface/

For getting interface descriptor and end point descriptor, we can use functions in IOUSBInterfaceInterface class

Link: http://developer.apple.com/library/mac/#documentation/Darwin/Reference/IOKit/IOUSBLib_h/Classes/IOUSBInterfaceInterface/