Re: Monotonic clock

Better yet, here is the direct code in Mac header file IOLib.h:

/*!
 * @group Raw Mach Time API
 * In general prefer to use the <time.h> API clock_gettime_nsec_np(3), which
 * deals in the same clocks (and more) in ns units.
 * Conversion of ns to (resp. from) tick units as returned by the mach time APIs
 * is performed by division (resp. multiplication) with the fraction returned by
 * mach_timebase_info().
 */

struct mach_timebase_info {
	uint32_t numer;
	uint32_t denom;
};

typedef struct mach_timebase_info *mach_timebase_info_t;
typedef struct mach_timebase_info  mach_timebase_info_data_t;

/*!
 * @function mach_timebase_info
 * Returns fraction to multiply a value in mach tick units with to convert it
 * to nanoseconds.
 *
 * @param info	Timebase fraction out parameter.
 * @result		KERN_SUCCESS if `info` was filled in.
 */
kern_return_t
mach_timebase_info(mach_timebase_info_t info);



> On Oct 9, 2025, at 08:08, David McClain (as dbm at refined-audiometrics dot com) <[email protected]> wrote:
> 
> I could be mistaken, but from my reading of the Apple docs, it appears that he has the ratio upside down:
> 
> https://github.com/Shinmera/precise-time/blob/main/darwin.lisp
> 
> 
> (define-constant MONOTONIC-TIME-UNITS-PER-SECOND
>     (cffi:with-foreign-objects ((tb :uint32 2))
>       (if (= 0 (cffi:foreign-funcall "mach_timebase_info" :pointer tb :int))
>           (let ((ticks-to-nanos (/ (cffi:mem-aref tb :uint32 1) (cffi:mem-aref tb :uint32 0))))
>             (floor (* 1000000000 ticks-to-nanos)))
>           (error "Failed to get time scale for monotonic time."))))
> 
> On my M1 iMac, mach_timebase_info returns the ratio 125/3. info numerator is at index 0, and denominator is at index 1.
> 
> 
> 
>> On Oct 9, 2025, at 07:39, Yacin Nadji (as yacin at defmacro dot cc) <[email protected]> wrote:
>> 
>>> On Oct 9, 2025, at 5:11 AM, Eugene Zaikonnikov (as ez at norphonic dot com) <[email protected]> wrote:
>>> 
>>> Hello,
>>> 
>>> Just wonder before I do it with FFI, is there already any support for
>>> reading monotonic clock? Or perhaps a library that covers LispWorks too?
>> 
>> isn’t that what get-internal-real-time does or am i mistaken? if i am or you want a library and more precision maybe check out shinmera’s precise time <https://shinmera.github.io/precise-time/> library. 
>> 
>> cheers
>> 
>> yacin
>