System Real-Time Clock (SYSRTC) Low-Power Integration#

The System Real-Time Clock (SYSRTC) is optimized for low-power operation across all SiWx917 power states. It continues running during sleep and deep-sleep modes, providing consistent timekeeping and wake-up capabilities without disrupting system activity.

Because SYSRTC operates from the always-on low-frequency domain, it keeps counting even when the main processor and high-performance peripherals are powered down. This design allows the device to wake predictably based on scheduled compare or alarm events, making SYSRTC ideal for battery-powered and energy-sensitive applications that require accurate timing during extended low-power operation.

Low-Power Design#

The SYSRTC peripheral is built on design principles that balance accuracy, flexibility, and power efficiency, allowing it to meet the requirements of both high-performance and ultra-low-power applications.

Key Principles#

1. Continuous operation: Maintains precise timekeeping and event scheduling across all power states.

2. Clock source flexibility: Supports both high-accuracy 32 kHz XTAL and low-power RC oscillators.

3. Efficient architecture: Uses a shared 32-bit counter to minimize switching and dynamic power consumption.

4. Smart wake-up: Provides accurate wake timing for scheduled or event-driven interrupts.

5. Resource optimization: Dynamically enables only required functions depending on the current power state.

Power State Strategy#

SYSRTC applies these principles through a well-defined power-management strategy. Each power state provides the optimal balance between functionality, accuracy, and energy savings.

• PS4 (High Performance): Full functionality with all groups, channels, and clock options active. Ideal for high-speed applications that require continuous timing operations.

• PS3 (Active/Performance Idle): Slightly reduced activity while preserving high accuracy; all compare/capture events remain operational.

• PS2: Most high-speed peripherals are gated, but SYSRTC continues timekeeping and wake scheduling with 32 kHz clock accuracy.

• PS1: Maintains essential timing and wake-up capability while minimizing leakage and switching power.

• PS0 (Deep Sleep): SYSRTC remains active with the a minimal configuration—using low-power RC or XTAL—to deliver basic timing and system wake events.

Note: SYSRTC resides in the always-on (AON) low-frequency domain and retains full functionality across all power states, including deep sleep.

Clock selection (XTAL vs. RC) defines the trade-off between accuracy and power. For most applications, XTAL is preferred for precision, while RC is suitable for energy-critical designs.

Clock Source Impact on Power Management#

The selected clock source directly affects both accuracy and power consumption.

• 32 kHz XTAL: Offers the highest accuracy but consumes more power.

• 32 kHz RC oscillator: Reduces power consumption but provides lower accuracy.

Power State Compatibility#

SYSRTC ensures consistent functionality across all power states. This compatibility provides developers with predictable behavior for timing, wake events, and peripheral control.

Comprehensive Power State Table#

Power State Features Summary#

Key Benefits: SYSRTC maintains 100% functionality across all power states, making it the ideal timing solution for low-power applications that require continuous operation.

Clock Source Stability Across Power States#

SYSRTC's clock source plays a critical role in determining timing stability and accuracy across power states. Developers can choose between XTAL and RC oscillator sources based on application needs.

32 kHz XTAL (Recommended for Low Power)#

32 kHz RC Oscillator#

Clock Source Selection Guidelines#

Note: The crystal oscillator provides superior accuracy and stability across all power states. Choose it for applications that require precise timing. The RC oscillator offers reduced accuracy but lower power consumption, making it useful for applications where power efficiency is more important than timing precision.

Power Consumption Optimization#

Power optimization depends on balancing clock source selection with application requirements. Developers should consider both accuracy and efficiency when designing low-power systems.

Clock Source Selection Impact#

Note: Use XTAL when timing accuracy is critical, such as in communication protocols or sensor sampling. Use RC when power efficiency is more important than absolute accuracy, such as for basic wake-up timers or simple scheduling.

Clock Domain Dependencies#

SYSRTC relies on the low-frequency clock domain for operation. This design ensures stable timing even when the system transitions between power states. Because SYSRTC operates independently of the main system clock, it remains a reliable timing mechanism regardless of system-level power management decisions.

Note: For a complete overview of power states across all timer peripherals, see the Power State Reference table in the main Timer Guide. For SYSRTC-specific information, see the Power State Reference table in the main SYSRTC guide.