ulong ticks(void)

#define	HZ          ...
#define	MS2HZ(t)    ...
#define	TK2SEC(t)   ...
#define	TK2MS(t)    ...
#define	MS2TK(m)    ...

Ticks returns the number of system-dependent clock ticks since system boot.

The system clock frequency is platform-dependent. Several symbolic constants and macro functions are defined by the file mem.h to convert between different time units:

HZ

The number of clock ticks per second.

MS2HZ

Milliseconds per clock tick.

TK2SEC(t)

Convert t clock ticks to seconds and return the result (truncating not rounding).

TK2MS(t)

Convert t clock ticks to milliseconds and return the result.

MS2TK(m)

Convert m milliseconds to clock ticks and return the result (truncating).

The functions are often used to calculate delays for timing functions, for instance:

if(atactlrwait(dp->cp, DHmagic, 0, MS2TK(100))){
	...
}