TimerGetPointer
The TimerGetPointer function retrieves a direct memory access pointer to the system's independent High-Resolution Timer (HRT). This clock operates as a continuous, un-slaved hardware ticker loop optimized for localized delta benchmarking, interval polling, and precision execution performance auditing.
Syntax
#include <mididll.h> PPULONG ppulHRTCurrentTime; /* Pointer to a ULONG pointer for clock mapping (Output) */ ULONG ulFlag; /* Reserved flag, must be 0 (Input) */ ULONG rc; /* Return code */ rc = TimerGetPointer(ppulHRTCurrentTime, ulFlag);
Parameters
- ppulHRTCurrentTime (PPULONG) - output
- A pointer to a caller-allocated `PULONG` (pointer to `ULONG`) variable. Upon a successful zero-return, this variable is populated with the direct memory address of the running 32-bit hardware high-resolution counter.
- ulFlag (ULONG) - input
- A reserved subsystem tracking modifier flag. This must be explicitly set to `0`.
Return Value
- rc (ULONG) - returns
- Returns `0` (or `TIMER_SUCCESS`) if the hardware clock mapping address was successfully extracted, or one of the following diagnostic error codes:
- TIMERERR_INVALID_PARAMETER: The context modifier flag ulFlag was not explicitly configured to `0`, or the memory address buffer provided for ppulHRTCurrentTime is null or unmappable.
- TIMERERR_INTERNAL_SYSTEM: An unrecoverable internal processing exception occurred while attempting to map the physical kernel timer pages into the calling application's memory context.
Remarks
- **System Clock Distinction Rules**: It is vital that application developers cleanly separate the functionality of the time tracking pointers available across the multimedia subsystem:
- TimerGetPointer maps a pointer to the global **High-Resolution Timer (HRT)**.
- MIDISetup yields a pointer directly linked to the virtualized **RTMIDI Subsystem Master Clock**.
- **Synchronization Behaviors**: Unlike the specialized RTMIDI clock loop, the hardware-driven high-resolution clock is entirely detached from the multi-client MIDI sequencing layer. It runs as a raw monotonic engine that cannot be scaled, frozen, adjusted, or slaved to external incoming transport synchronization lines (such as MTC, MIDI Clock pulses, or linear SMPTE hardware feeds).
- **Scheduling Restriction Warnings**: Because the HRT runs independently of stream events, developers **must not** use the absolute 32-bit integer value read from the ppulHRTCurrentTime tracking address to compute or assign scheduling timestamps (`ulTime` inside the MESSAGE structure) for the MIDISendMessages pipeline. Utilizing this value for stream playback will induce temporal displacement, packet drops, or critical scheduling failures inside the underlying event queue manager. Use this pointer strictly for internal software profiling, performance telemetry, or non-MIDI-bound loop intervals.