maczilla:~ bart$ pmset -g assertions
20-02-14 11:53:09 CET    
Assertion status system-wide:
BackgroundTask                 0
PreventDiskIdle                0
ApplePushServiceTask           0
UserIsActive                   0
PreventUserIdleDisplaySleep    0
InteractivePushServiceTask     0
PreventSystemSleep             0
ExternalMedia                  0
PreventUserIdleSystemSleep     0
NetworkClientActive            0
Kernel Assertions: 0x104=USB,MAGICWAKE
id=500  level=255 0x4=USB mod=29-01-14 17:39 description=EHC1 owner=AppleUSBEHCI
id=501  level=255 0x4=USB mod=20-02-14 10:58 description=EHC2 owner=AppleUSBEHCI
id=502  level=255 0x100=MAGICWAKE mod=14-02-14 07:56 description=en0 owner=en0

maczilla:~ bart$ pmset -g assertions
20-02-14 11:54:15 CET    
Assertion status system-wide:
BackgroundTask                 0
PreventDiskIdle                0
ApplePushServiceTask           0
UserIsActive                   0
PreventUserIdleDisplaySleep    0
InteractivePushServiceTask     0
PreventSystemSleep             0
ExternalMedia                  0
PreventUserIdleSystemSleep     1
NetworkClientActive            0
Listed by owning process:
pid 148(coreaudiod): [0x0000000100001e8b] 00:00:04 NoIdleSleepAssertion named: "com.apple.audio.'AppleHDAEngineOutput:1B,0,1,2:0'.noidlesleep"
Kernel Assertions: 0x104=USB,MAGICWAKE
id=500  level=255 0x4=USB mod=29-01-14 17:39 description=EHC1 owner=AppleUSBEHCI
id=501  level=255 0x4=USB mod=20-02-14 10:58 description=EHC2 owner=AppleUSBEHCI
id=502  level=255 0x100=MAGICWAKE mod=14-02-14 07:56 description=en0 owner=en0

PreventUserIdleSystemSleep     1
NetworkClientActive            0
Listed by owning process:
pid 195(coreaudiod): [0x0000000100001e8b] 00:00:04 NoIdleSleepAssertion named: "com.apple.audio.'AppleHDAEngineOutput:1B,0,1,2:0'.noidlesleep"



jens-macpro:~ jensverwiebe$ ps u -p 195
USER          PID  %CPU %MEM      VSZ    RSS   TT  STAT STARTED      TIME COMMAND
_coreaudiod   195   1,2  0,1  2566812   9528   ??  Ss   11:24am   0:29.80 /usr/sbin/coreaudiod

To participate in power management decisions, you'll need to add your device driver to the power management plane, typically in your overridden IOService::start(provider) method:

PMinit();
provider->joinPMtree(this);
registerPowerDriver(this, powerStates, numPowerStates);
where powerStates and numPowerStates specifies an array of power states you want your device to be able to be in. You'll probably not want more than 2 for a virtual device, and maybe you even only need one. I suspect a superclass of your class is setting states that are inhibiting sleep. Once you've registered for power management, your driver will be expected to handle the power management methods such as IOService::setPowerState().

#import <IOKit/pwr_mgt/IOPMLib.h>

// kIOPMAssertionTypeNoDisplaySleep prevents display sleep,
// kIOPMAssertionTypeNoIdleSleep prevents idle sleep

//reasonForActivity is a descriptive string used by the system whenever it needs 
//  to tell the user why the system is not sleeping. For example, 
//  "Mail Compacting Mailboxes" would be a useful string.

//  NOTE: IOPMAssertionCreateWithName limits the string to 128 characters. 
CFStringRef* reasonForActivity= CFSTR("Describe Activity Type");

IOPMAssertionID assertionID;
IOReturn success = IOPMAssertionCreateWithName(kIOPMAssertionTypeNoDisplaySleep, 
                                    kIOPMAssertionLevelOn, reasonForActivity, &assertionID); 
if (success == kIOReturnSuccess)
{

    //Add the work you need to do without 
    //  the system sleeping here.

    success = IOPMAssertionRelease(assertionID);
    //The system will be able to sleep again. 
}