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Single-chip microcomputer as the core embedded system low-power design - Database & Sql Blog Articles
In embedded systems, power consumption has become a critical concern, especially in portable devices that rely on battery power. Reducing power usage not only extends battery life but also lowers operational costs. For microcontroller-based (MCU) systems, minimizing power consumption involves both hardware and software design considerations. While this article focuses on hardware and application-level software strategies, it's important to note that real-time operating systems (RTOS) also play a role in power management.
1. **Hardware Design for Low Power**
1.1 **Choose a Simple CPU Core**
When selecting an MCU, avoid over-specifying the CPU core. An 8-bit microcontroller may be sufficient for many applications, eliminating the need for a more complex 16-bit or 32-bit device. Simpler cores consume less power and are more cost-effective. While higher-performance MCUs offer advanced features, they often come with increased power consumption due to higher transistor counts and leakage currents. Even in low-power modes, these cores can still draw significant current if not properly managed.
1.2 **Use a Low-Voltage Power Supply**
Reducing the supply voltage is one of the most effective ways to lower power consumption. Modern MCUs now operate at voltages as low as 1.8V, down from the traditional 5V. This reduction is made possible by advances in semiconductor technology, such as smaller process nodes (e.g., 0.13μm). However, lower voltages also increase leakage current, which can offset some of the benefits. Despite this, low-voltage MCUs are becoming increasingly popular due to their energy efficiency.
1.3 **Utilize Low-Power Modes**
MCUs typically have multiple low-power modes, such as "wait" and "stop." In wait mode, the CPU is halted, but the system clock continues, allowing peripherals to remain active. This mode consumes about 50–70% of the active power. In stop mode, the clock is disabled, and the MCU is woken up by an external interrupt. This can reduce current consumption to the microampere range, and in deep stop mode, it can drop below 20nA. However, entering deep stop mode requires careful handling of data retention, as RAM contents are lost.
1.4 **Optimize Clock Configuration**
The choice of clock source significantly impacts power consumption. Using a lower frequency clock reduces switching activity, thus lowering power use. Internal oscillators are convenient but less accurate than external crystals. Phase-locked loops (PLLs) allow flexible clock control but add to power consumption. For the lowest power, using an external crystal without a PLL is often the best option.
2. **Software Optimization for Power Efficiency**
2.1 **Use Interrupts Instead of Polling**
Interrupt-driven designs allow the CPU to sleep until an event occurs, reducing unnecessary wake-ups. Polling, on the other hand, forces the CPU to constantly check I/O registers, increasing power use. Implementing interrupts helps save energy, especially in applications where events are infrequent.
2.2 **Replace Subroutines with Macros**
Calling subroutines involves pushing and popping register values onto the stack, which increases RAM access and power consumption. Using macros instead can eliminate this overhead, although it may increase code size. With modern MCUs having larger Flash memory, this trade-off is often worth it.
2.3 **Minimize CPU Workload**
Reduce CPU operations by precomputing results, using lookup tables, and avoiding unnecessary calculations. Use efficient data types and avoid floating-point operations when possible. These steps help reduce the time the CPU spends active, thereby saving power.
2.4 **Power Down Unused Peripherals**
Unused I/O pins and peripheral modules should be turned off to minimize leakage current. For example, RS232 drivers can be controlled via an I/O pin and powered down when not in use. Uninitialized I/O pins can lead to unexpected current draw, so proper configuration is essential.
3. **Conclusion**
A successful low-power design requires a balance between hardware and software optimization. From selecting the right MCU to implementing efficient software practices, every decision impacts overall power consumption. As battery-powered devices become more common, understanding and applying these techniques will be crucial for future embedded system designers.