Time sources

Source	Driver	Command	Role
PIT	kernel/core/core_timer.c	timer	THE tick: 100 Hz, scheduler, soft timers
HPET	drivers/time/driver_hpet.c	hpet	high-res counter
ACPI PM timer	drivers/time/driver_pmtimer.c	pmtimer	legacy fallback
TSC	drivers/time/driver_tsc.c	tsc	cycle counter
CMOS RTC	drivers/time/driver_cmos_rtc.c	rtc	wall clock

The tick stays PIT - one 10 ms heartbeat for the whole machine; the others are read-only precision sources (and rtc sets/reads wall time). The E2E timer suite verifies monotonicity and cross-source consistency.