Re: Getting String Descriptors in Mac OS X User-land

• Subject: Re: Getting String Descriptors in Mac OS X User-land
• From: Ron Wilson <email@hidden>
• Date: Mon, 19 Jan 2004 22:25:34 -0800

Hi Ashley,

I do this:

(given stringIndex)

IOReturn err;

UInt8 stringDescLenInBytes;

IOUSBDevRequest devRequest;
devRequest.bmRequestType	= 0x80;		// device to host
devRequest.bRequest		= 0x06;		// GET_DESCRIPTOR
devRequest.wValue			= (0x0003 << 8) | stringIndex;
devRequest.wIndex			= 0;
devRequest.wLength		= 0x0001;
devRequest.pData			= &stringDescLenInBytes;

err = (*dev)->DeviceRequest(dev, &devRequest);
if (err == kIOReturnSuccess && stringDescLenInBytes > 0)
{
	UInt8* stringDescriptor = new UInt8[stringDescLenInBytes];
	devRequest.wLength = stringDescLenInBytes;
	devRequest.pData = stringDescriptor;

	err = (*dev)->DeviceRequest(dev, &devRequest);
	if (err == kIOReturnSuccess)
	{
		UInt8* descStr8Ptr = stringDescriptor + 2;
		UniChar* descStrPtr = reinterpret_cast<UniChar*>(descStr8Ptr);
		CFIndex uniStrLen = (stringDescLenInBytes - 2) / 2;

		// Note bytes will be swapped (USB is little endian)
		SwapUniCodeBytes(descStrPtr, uniStrLen);
		
		// now create a CFString from the UTF-16 bytes
		...
	}

	delete [] stringDescriptor;
}

--Ron

Hi,
I am writing a program that lists all of the devices attached to the computer via usb and details about them (similar to USBProber) so that people can choose the device they have designed containing a FTDI232BM USB to Serial chip and program their vendor id, product id and other information into the onboard EEPROM.

So far I have obtained the list of all of the devices on the bus and from them most of the information I need but I also want to get the Manufacturer, Product and Serial Number strings.

So far I have got the string indicies for the 3 strings but I don't know what to do next. I have looked at the docs on the developer website but I have only found how to do it from within the kernal. How do I, from my carbon app written in C, obtain a copy of the strings?

  Thanks for any help,

  Regards,

  Ashley

========================================================
Ashley Butterworth
BLUEsat Project
Website: http://www.bluesat.unsw.edu.au/
Email: email@hidden
Mobile: 0403-979-560
BLUEsat Office: +61 (0)2 9385-4498
BLUEsat Fax: +61 (0)2 9385-5993
========================================================
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