Cycle-Accurate Real-Time Clocks for Low-Power Timestamping
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Solution Overview
Problem
In low-power applications like battery-operated devices, the power-down and restart of processors lead to inaccurate determination of time differences between events due to the processor's clock being powered down, making cycle-accurate timestamping unreliable.
Innovation Solution
A cycle-accurate real-time clock system that includes a selectively-operable CPU clock and a continuously-operating backup clock, with a multiplexer and time computing device to maintain and provide cycle-accurate timestamps even when the CPU clock is disabled, using counters and a gauge computing device to synchronize and adjust clock values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the processor's clock is powered down to reduce power consumption, then energy efficiency is improved, but timestamp accuracy deteriorates
Solution Approach 1:
The real-time clock is segmented into two independent counter systems: a first counter that operates only when the CPU clock is active, and a second counter that continuously operates using a backup clock. This segmentation allows each counter to serve specific purposes - the first for high-precision cycle counting during active periods, and the second for continuous time tracking during power-down periods - thereby maintaining timestamp accuracy while enabling power savings.
Solution Approach 2:
A multiplexer acts as an intermediary between the two counter systems and the output interface. It selectively routes either the first counter's output (when CPU clock is active) or the second counter's output (when CPU clock is powered down) to the timestamp output. This intermediary mechanism ensures seamless transition between power states while maintaining continuous, accurate timestamp generation without requiring the CPU clock to remain continuously powered.
2Loss of energy
If the processor clock is selectively powered down, then power consumption is reduced, but the ability to determine time differences between events deteriorates
Solution Approach 1:
The second counter continuously accumulates time information using the backup clock even when the CPU clock is powered down. This preliminary action ensures that time information is not lost during power-down periods, as the second counter is already tracking elapsed time in advance. When the CPU clock is restarted, the system can immediately provide accurate time difference calculations without needing to reinitialize or lose tracking information.
3Device complexity
If a single counter is used for timestamping, then device complexity is reduced, but reliability deteriorates during power-down states
Solution Approach 1:
The system dynamically adapts its operational mode based on the power state. When the CPU clock is active, the first counter operates and provides high-precision timestamps. When the CPU clock is powered down, the system automatically switches to using the second counter driven by the backup clock. This dynamic behavior ensures the system maintains reliable timestamping functionality across different power states without requiring a single complex continuously-operating high-precision counter.
Data Source
AI summary
Cycle-accurate real-time clocks and methods to operate the same are disclosed. An example real-time clock comprises a first counter to count cycles of a selectively-operable clock, a multiplexer to select from at least an output signal associated with the first counter or a continuously-operating clock, and a second counter to count cycles of an output signal of the multiplexer.