Real-Time Priority System Levels (Windows Embedded CE 6.0)

1/6/2010

The priority system has 256 Priority Levels numbered 0 (zero) through 255. Priority level 0 is the highest priority level. The original eight priority levels for Windows CE 2.12 and earlier versions are mapped to levels 248 through 255.

Applications and device drivers should use the CeGetThreadPriority and CeSetThreadPriority APIs, instead of the legacy APIs, GetThreadPriority and SetThreadPriority. The legacy APIs are still available with the same interfaces as before, but those APIs have access to only the original eight priority levels.

The priority level system is divided into four ranges. The following table shows these ranges.

Levels	Description
0 through 96	Reserved for real-time above drivers.
97 through 152	Used by the default Windows Embedded CE–based device drivers.
153 through 247	Reserved for real-time below drivers.
248 through 255	Mapped to non-real-time priorities.

The following table shows the default priority levels that are associated with device drivers. You can override these values by changing the source code for the drivers or by setting values in the registry. The registry paths in the table assume that the root Drivers key is HKEY_LOCAL_MACHINE\Drivers\BuiltIn; the registry uses hexadecimal values for the priority levels.

Decimal priority	Hexadecimal priority	Device driver	Override
99	0x63	Power Manager resume thread	HKEY_LOCAL_MACHINE\CurrentControlSet\Control\Power\ResumePriority256
100	0x64	USB Function	None
101, also uses +1 and -1 relative priorities	0x65, also uses +1 and -1 relative priorities	USB OHCD	HKEY_LOCAL_MACHINE\Drivers\BuiltIn\OHCI\Priority256
101, also uses +1, +3, +5 and +7 relative priorities	0x65, also uses +1, +3, +5, and +7 relative priorities	USB UHCD	HKEY_LOCAL_MACHINE\Drivers\BuiltIn\UHCI\Priority256
103	0x67	Serial	HKEY_LOCAL_MACHINE\Drivers\BuiltIn\Serial\Priority256
105, also uses +1 and +2 relative priorities	0x69, also uses +1 and +2 relative priorities	PCMCIA	HKEY_LOCAL_MACHINE\Drivers\PCMCIA\Priority256
109	0x6D	Touch	HKEY_LOCAL_MACHINE\Drivers\BuiltIn\Touch\Priority256
110, also uses +2 and +4 relative priorities	0x6E, also uses +2 and +4 relative priorities	IRSIR	HKEY_LOCAL_MACHINE\Comm\Irsir1\Parms\Priority256
116, also uses +2, +4, +6, +8, +10 and +12 relative priorities	0x74, also uses +2, +4, +6, +8, +10, and +12 relative priorities	NDIS	HKEY_LOCAL_MACHINE\Drivers\BuiltIn\NDIS\Priority256
131	0x83	KITL	Override in the OEM Application Layer
131	0x83	VMINI	HKEY_LOCAL_MACHINE\Comm\VMini\Priority256
132	0x84	CxPort	HKEY_LOCAL_MACHINE\Comm\Cxport\Priority256
145	0x91	PS/2 Keyboard	HKEY_LOCAL_MACHINE\HARDWARE\DEVICEMAP\KEYBD\Priority256
148	0x94	IR Comm	HKEY_LOCAL_MACHINE\Drivers\BuiltIn\IrComm\Priority256
150	0x96	TAPI (Unimodem)	HKEY_LOCAL_MACHINE\Drivers\Unimodem\Priority256
210	0xD2	WaveDev	HKEY_LOCAL_MACHINE\Drivers\BuiltIn\WaveDev\Priority256
248	0xF8	PM (Power Manager)	HKEY_LOCAL_MACHINE\CurrentControlSet\Control\Power\Priority256
249	0xF9	PS/2 Mouse	HKEY_LOCAL_MACHINE\HARDWARE\DEVICEMAP\MOUSE\Priority256
249	0xF9	Power Manager device registration thread	HKEY_LOCAL_MACHINE\CurrentControlSet\Control\Power\PnPPriority256
249	0xF9	Power Manager system management thread	HKEY_LOCAL_MACHINE\CurrentControlSet\Control\Power\SystemPriority256
249	0xF9	Power Manager activity timer thread	HKEY_LOCAL_MACHINE\CurrentControlSet\Control\Power\TimerPriority256
250	0xFA	WaveAPI	HKEY_LOCAL_MACHINE\Drivers\BuiltIn\WAPIMAN\Priority256
251	0xFB	Power Manager battery monitor thread	HKEY_LOCAL_MACHINE\CurrentControlSet\Control\Power\PowerPollPriority256

Remarks

Threads in Normal (as apposed to Privileged) applications can use thread priorities 248 through 255.

Threads in Privileged applications can use any thread priority.

For more information about creating a Privileged environment, see Trusted Environment Creation.

See Also

Concepts

Real-Time Priority System
Real-Time Priority System Response Times