Samsung S5PC100 User Manual page 219

Power Management S5PC100 USER'S MANUAL (REV1.0)
5.4 RTC ALARM
The Real Time Clock (RTC) has 32-bit counter used to wake up the system after the specified time. If the timer
alarm happens, PMU wakes up the system and sets the RTL_ALARM_WAKEUP field of WAKEUP_STAT register
to 1. After the wake-up, Cortex-A8 refers the WAKEUP_STAT register to find out what caused the wake-up.
5.5 TICK
The Real Time Clock (RTC) has tick counter function to be used for wakeup source from power down mode as
specified in Table 2.4-7. In NORMAL mode, RTC time tick may be used for real time operating system (RTOS)
kernel time tick.
5.6 SYSTEM TIMER
System Timer is newly introduced module in S5PC100 to supplement the disadvantage of the existing PWM timer.
In IDLE mode, the existing PWM timer generates interrupts at fixed interval using auto-reload function, so it wakes
up the chip too often. If the PWM timer generates an interrupt at various interval using one-shot mode, but it
accumulates the timing inaccuracy since it cannot count time during manual setting, and therefore it cannot
generate accurate 1ms timing tick to be used for OS operation.
In DEEP-IDLE, STOP, and DEEP-STOP mode, there is no system clock if Top domain is power-off. Therefore,
RTC is used for generating timing tick instead of PWM timer, but by using this clock, timing count is not controlled
to meet exact 1ms OS time tick since RTC clock does not have high resolution.
On the other hand, System timer has the function of generating interrupts at various interval, and do not require
manual setting, so it does not wakes up the chip too often, and provides accurate 1ms timing ticks. System timer
uses one of an external crystal clock , RTC clock and the generated clock from CLKCON as clock input.
For System Timer to operate in DEEP-IDLE, STOP, and DEEP-STOP mode, power to System Timer is on. The
wakeup event from System Timer will wake up S5PC100 from DEEP-IDLE, STOP, and DEEP-STOP mode.
2.4-20