Processor System Stack Pointer Management for Low-Power IoT
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Solution Overview
Problem
Processor systems in low-power devices like IoT devices face challenges in minimizing power consumption during inactive states without compromising performance, as existing power management techniques require full re-initialization of RAM during mode transitions, leading to increased power consumption and potential stack corruption.
Innovation Solution
The processor system employs a secondary RAM region as a stack and uses a RAM-image to transition between operating modes by copying hardware configuration parameters and program context data from non-volatile memory, reducing the need for full re-initialization and minimizing power consumption by powering down RAM without losing volatile data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If full re-initialization of RAM is performed during mode transitions, then system reliability is improved, but power consumption increases and transition time increases
Solution Approach 1:
The patent segments the stack operations into two distinct phases: a first stack phase during RAM retention where the stack operates in the first RAM region, and a second stack phase during RAM re-initialization where the stack operates in the second RAM region. This segmentation allows the system to maintain reliability during transitions while minimizing power consumption by only re-initializing RAM when necessary and using appropriate stack regions for each phase.
2Use of energy by moving object
If RAM is powered off during standby mode, then power consumption is reduced, but transition speed to normal mode decreases
Solution Approach 1:
The patent applies preliminary action by saving the stack pointer value to a register before powering off the RAM during standby mode. This preliminary preservation of critical stack information enables the system to rapidly restore the stack operation upon waking from standby, thereby maintaining fast transition speed while benefiting from reduced power consumption during the inactive period.
3Speed
If RAM is retained during standby mode, then transition speed is improved, but power consumption increases due to leakage current
Solution Approach 1:
The patent implements a dynamic approach by adaptively managing the stack pointer based on the operational phase. During the first phase (RAM retained), the stack pointer operates in the first RAM region for fast access. During the second phase (RAM re-initialized), the stack pointer transitions to the second RAM region. This dynamic adaptation allows the system to optimize between transition speed and power consumption by selecting the appropriate stack region for each operational state.
4Device complexity
If stack pointer is not preserved during mode transition, then system complexity is reduced, but stack corruption occurs
Solution Approach 1:
The patent introduces a register as an intermediary element to preserve the stack pointer value during mode transitions. This intermediary mechanism bridges the gap between the first and second stack phases, ensuring that critical stack information is maintained throughout the transition process. The register acts as a temporary storage medium that prevents stack corruption while adding minimal complexity to the system.
Data Source
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AI summary
A processor system and method is described. The processor system includes a central processing unit (CPU) comprising a register for storing a stack pointer value, a non-volatile memory coupled to the CPU and having a first non-volatile memory region configured to store instructions executable by the CPU and a second non-volatile memory region configured to store a RAM-image comprising program context data. The processor system includes a random-access memory (RAM) coupled to the CPU and having a first RAM region and a second RAM region. The processor system is configured to have a first operating mode where the RAM data values are not retained and a second operating mode where the RAM is powered on. In operation, the processor system changes from the first operating mode to the second operating mode by applying power to the RAM, setting the stack pointer value to an address in the second RAM region, copying the program context data from the second non-volatile memory region to the first RAM region, and setting the stack pointer value to an address within a segment of the first RAM region.