Mac IOKit USB signal detection - macos

Question

matchingDict = IOServiceMatching(kIOUSBDeviceClassName);
numberRef = CFNumberCreate(kCFAllocatorDefault, kCFNumberSInt32Type, &vendorId);
CFDictionarySetValue(matchingDict, CFSTR(kUSBVendorID), numberRef);
CFRelease(numberRef);
numberRef = CFNumberCreate(kCFAllocatorDefault, kCFNumberSInt32Type, &deviceProductId);
CFDictionarySetValue(matchingDict, CFSTR(kUSBProductID), numberRef);
CFRelease(numberRef);
numberRef = NULL;
kr = IOServiceAddMatchingNotification(gNotifyPort,
kIOFirstMatchNotification,
matchingDict,
DeviceAdded,
NULL,
&gAddedIter);
For handle the notification while add the usb device to Mac pc is ok, but can i getting the signal while user press the button on the usb device?
Thanks ALL!

Answer 1

If a user presses a button on a device, this will not create a device notification. Unless this is a device Apple has a driver for (in which case you may receive an input event, e.g. an NSEvent), you will have to get the device interface and talk to that device through its interface. E.g. USB devices have interfaces, each interface has endpoints and the connections to those endpoints are labeled pipelines. There are outgoing and incoming pipelines and you can send data to or read data from those pipelines. Different kind of pipelines exist, bulk, isochronous and interrupt pipelines. Further every device has a control pipe, the only pipeline you can use bidirectionally.
Apple ships a tool named USB Prober with Xcode, have a look at your USB devices with it. E.g. my Apple Cinema Display, also connected via USB, reports the following:
Full Speed device # 3 (0xFD520000): ............................................. Composite device: "Apple Cinema HD Display"
Port Information: 0x0019
Captive
External Device
Connected
Enabled
Device Descriptor
Descriptor Version Number: 0x0110
Device Class: 0 (Composite)
Device Subclass: 0
Device Protocol: 0
Device MaxPacketSize: 8
Device VendorID/ProductID: 0x05AC/0x9223 (Apple Inc.)
Device Version Number: 0x0114
Number of Configurations: 1
Manufacturer String: 1 "Apple Computer, Inc."
Product String: 2 "Apple Cinema HD Display"
Serial Number String: 0 (none)
Configuration Descriptor
Length (and contents): 34
Raw Descriptor (hex) 0000: 09 02 22 00 01 01 00 E0 01 09 04 00 00 01 03 00
Raw Descriptor (hex) 0010: 00 00 09 21 11 01 00 01 22 37 00 07 05 81 03 08
Raw Descriptor (hex) 0020: 00 10
Number of Interfaces: 1
Configuration Value: 1
Attributes: 0xE0 (self-powered, remote wakeup)
MaxPower: 2 ma
Interface #0 - HID
Alternate Setting 0
Number of Endpoints 1
Interface Class: 3 (HID)
Interface Subclass; 0
Interface Protocol: 0
HID Descriptor
Descriptor Version Number: 0x0111
Country Code: 0
Descriptor Count: 1
Descriptor 1
Type: 0x22 (Report Descriptor)
Length (and contents): 55
Raw Descriptor (hex) 0000: 05 80 09 01 A1 01 15 00 26 FF 00 75 08 85 02 96
Raw Descriptor (hex) 0010: 01 01 09 02 B2 02 01 05 82 95 02 85 10 09 10 B1
Raw Descriptor (hex) 0020: 02 25 04 85 D6 09 D6 B1 02 25 07 85 E7 B1 02 26
Raw Descriptor (hex) 0030: FF 00 85 E4 81 02 C0
Parsed Report Descriptor:
Usage Page (Monitor)
Usage 1 (0x1)
Collection (Application)
Logical Minimum......... (0)
Logical Maximum......... (255)
Report Size............. (8)
ReportID................ (2)
Report Count............ (257)
Usage 2 (0x2)
Feature................. (Data, Variable, Absolute, No Wrap, Linear, Preferred State, No Null Position, Nonvolatile, Buffered bytes)
Usage Page (VESA Virtual Controls)
Report Count............ (2)
ReportID................ (16)
Usage 16 (0x10)
Feature................. (Data, Variable, Absolute, No Wrap, Linear, Preferred State, No Null Position, Nonvolatile, Bitfield)
Logical Maximum......... (4)
ReportID................ (214)
Usage 214 (0xd6)
Feature................. (Data, Variable, Absolute, No Wrap, Linear, Preferred State, No Null Position, Nonvolatile, Bitfield)
Logical Maximum......... (7)
ReportID................ (231)
Feature................. (Data, Variable, Absolute, No Wrap, Linear, Preferred State, No Null Position, Nonvolatile, Bitfield)
Logical Maximum......... (255)
ReportID................ (228)
Input................... (Data, Variable, Absolute, No Wrap, Linear, Preferred State, No Null Position, Bitfield)
End Collection
Endpoint 0x81 - Interrupt Input
Address: 0x81 (IN)
Attributes: 0x03 (Interrupt no synchronization data endpoint)
Max Packet Size: 8
Polling Interval: 16 ms
This device has one Interface, Interface #0 and there exist one endpoint on this interface (0x81), which is connected through an interrupt pipeline, that can transfer packets up to 8 bytes in size every 16 ms. If you'd now want to communicate with that pipeline, you'll have to get the USB driver interface of the device and this interface offers functions to communicate with the pipeline in question, synchronously or asynchronously, it's all pretty similar to network code.
If you now ask yourself, what this pipeline is good for at a monitor in the first place, it's how the monitor communicates button presses to the system. Apple's Cinema Displays have 3 buttons, "+" and "-" for brightness and a power button. The functionality of the power button is configurable in the system prefs, e.g. it can send the whole Mac to sleep if I want that. Whenever I hit one of those button, an interrupt event is created and sent via this USB pipe to the system (actually the system has to poll for such an event every 16 ms, but the system does that for you - your code can pretend the event was pushed by the monitor).
Have a look at the IOUSBDeviceInterface197, and please note, that it inherits of IOUSBDeviceInterface187, which inherits of IOUSBDeviceInterface182, which again inherits of IOUSBDeviceInterface. That means if you retrieve a 197 version of the interface, all methods of the interfaces it inherits from are available for this interface as well (they are just not listed again on the page). Apple has to use interface with versions in the name to stay compatible with older code. Apple extended the USB interfaces over the time (e.g. with new OS X releases) and to be sure that old code still runs, they always added a new interfaces, otherwise they'd break existing code.
Here you get a list of all these interfaces. Yes, the documentation is horrible. You have to learn by try and and/or and sample code. Please note there are DeviceInterfaces and InterfaceInterfaces; that's not the same thing. A DeviceInterface is the driver interface to a device itself, every device can have multiple "USB interfaces" (this is a term of the USB standard) and the interface to such an "usb interface" is named an "InterfaceInterface". Simple devices, as the monitor shown above, only have a single interface, though.
You think that this is darn complicated? Well, most developers from other platforms say, that once they figured out how all this stuff works, Mac OS is the easiest of all platforms if you need raw access to USB pipes. However, it gets even worse: Every interface can have multiple configurations and you can set a configuration on the interface which might change the pipelines (e.g. in one configuration a pipe is a bulk pipe and in another one the very same pipe is now an isochronous pipe). You can see all this in the USB Prober application (it shows alternative configuration). And please note, that an USB device can have a completely different set of interfaces, pipelines and configurations for different speeds (e.g. one for USB 1.2, aka low + full speed, and one for USB 2, aka hi-speed).
Apple tries to explain most of the USB basics you should know before you start writing any code on this page. And if you click on "Working With USB Device Interfaces", Apple even has plenty of sample code for you how to get a DeviceInterface, which you can use to get InterfaceInterfaces.
I hope I could get you some pointers and some interesting links for reading. It's not really the answer to your question, but it is a good start. Of course, you could also write a kernel driver (kernel extension) to add support for your device to the system, so that pressing the button generates an event that any software can handle without having to use IOKit at all... but I somehow doubt you want to go there.