Intel C2518 FH8065501516710 Data Sheet

Intel

®

 Atom™ Processor C2000 Product Family for Microserver

September 2014

Datasheet, Vol. 2 of 3

Order Number: 330061-002US

523

The RTC module provides a battery backed-up date and time keeping device. Three 

interrupt features available are time of day alarm with once-a-second to once-a-month 

range, periodic rates of 122 ms to 500 ms, and end-of-update cycle notification. 

Seconds, minutes, hours, days, day of week, month, and year are counted. The hour is 

represented in a twelve or twenty-four hour format, and data are represented in BCD 

or binary format. The design is meant to be functionally compatible with the Motorola* 

MS146818B. The time keeping comes from a 32.768-kHz oscillating source, which is 

divided to achieve an update every second. The lower 14 bytes on the lower RAM block 

have specific functions. The first ten are for time and date information. The next four 

(0Ah to 0Dh) are registers, which configure and report RTC functions. A host-initiated 

write takes precedence over a hardware update if a collision.

An update cycle occurs once a second, if the B.SET bit is not asserted and the divide 

chain is properly configured. During this procedure, the stored time and date are 

incremented, overflow checked, a matching alarm condition is checked, and the time 

and date are rewritten to the RAM locations. The update cycle starts at least 488 ms 

after A.UIP is asserted, and the entire cycle does not take more than 1984 ms to 

complete. The time and date RAM locations (00h to 09h) are disconnected from the 

external bus during this time.

The real-time clock interrupt is internally routed within the SoC both to the I/O APIC 

and the 8259. It is mapped to interrupt vector 8. This interrupt does not leave the SoC, 

nor is it shared with any other interrupt. IRQ8# from the Serial IRQ (SERIRQ) stream is 

ignored. However, the High Performance Event Timers (HPET) are also mapped to 

IRQ8#; in this case, the RTC interrupt is blocked.

Once a range is locked, the range is unlocked only by a hard reset, which invokes the 

BIOS and allow it to re-lock the RAM range.