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4.15. Real Time Clock, RTC

The PL031 PrimeCell Real Time Clock Controller (RTC) is an AMBA compliant SoC peripheral that is developed, tested, and licensed by ARM Limited.

A counter in the RTC is incremented every second. The RTC can therefore be used as a basic alarm function or long time-base counter.

The current value of the clock can be read at any time or the RTC can be programmed to generate an interrupt after counting for a programmed number of seconds. The interrupt can be masked by writing to the interrupt match set or clear register.

Table 4.80. RTC implementation
Location Southbridge
Memory base address0x10017000
Interrupt 42
Release versionARM RTC PL031 r1p0
Reference documentationARM PrimeCell Real Time Clock (PL031) Technical Reference Manual


There is also a separate Time-of-Year (TOY) implemented in an external RTC chip (DS1338) on the baseboard. The external RTC can be accessed by the serial bus interface (see Two-wire serial bus interface, SBCon). For details on the programming interface to the Time-of-Year RTC, see the data sheet for the Maxim DS1338 integrated circuit (

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