AN1517: SiWG917 Real-Time Clock (RTC) Management Application Note#

The Real-Time Clock (RTC) subsystem in the SiWG917 enables precise timekeeping and scheduled wake-ups while maintaining ultra-low-power (ULP) operation. Located in the Ultra-Ultra-Low-Power (UULP) domain, the RTC continues running even when the M4 core is in sleep mode, ensuring timekeeping continuity across sleep cycles. The Calendar/Alarm and System Real-Time Counter (SYSRTC) blocks together support human-readable timekeeping and fine-grained tick-based scheduling.

When the application is idle, the Power Manager coordinates clock gating and domain retention. The Calendar can wake the system through alarms or periodic triggers, and the SYSRTC provides precise tick timing and wakeup scheduling for Real-Time Operating System (RTOS) Tickless Idle.

This architecture delivers predictable wake-up behavior with low drift and seamless integration with system power states—critical for energy-efficient IoT designs that require continuous timing and scheduled wake-ups in deep-sleep environments.

Key Points#

• RTC architecture in the UULP domain with continuous operation during sleep.

• Calendar, Alarm, and SYSRTC features for timekeeping, scheduling, and wake event control.

• Guidance on choosing and configuring crystal (XTAL) versus resistor-capacitor (RC) clock sources for accuracy vs. power trade-offs.

• Power Manager coordination: RTC blocks can serve as wake sources and SYSRTC supports RTOS Tickless Idle architectures.

• Includes debugging tips and best-practice references for low-power timing and wake reliability.