The Portenta C33 Low Power Library is a library designed to optimize power consumption for projects using the Portenta C33 boards, which are powered by the Renesas RA6M5 microcontroller. The library achieves this by providing access to various low power modes. These modes are essential for applications where power efficiency is crucial, such as in remote sensing, IoT devices, or battery-powered applications.
- WakeFromGPIO - This example demonstrates how you can use the GPIO pins to wake your board from sleep.
- WakeFromRTC - This example demonstrates how you can use the RTC to wake the board from sleep.
- Function: Reduces the microcontroller's power usage to about half of its normal consumption.
- Effect: Upon waking up from this mode, the execution of your program resumes exactly where it stopped. This is particularly useful for applications that require a quick resume with minimal power savings.
- Wake-Up Triggers: The board can be configured to wake up either from an RTC alarm or an external interrupt pin.
- Function: Significantly reduces power usage to approximately 100uA (when all peripherals are off), making it ideal for long-term, battery-dependent operations.
- Effect: Unlike Sleep Mode, waking up from Deep Sleep Mode restarts the board, triggering the void setup() function. This behavior is suitable for scenarios where a full reset is acceptable or desired upon waking up.
- Wake-Up Triggers: The board can be configured to wake up either from an RTC alarm or an external interrupt pin.
Here's an overview of the reduction in power usage that you can expect from this library.
| Mode | Peripherals | Current |
|---|---|---|
| Normal Operation | Off | 41.37mA |
| Sleep | On | 18.26mA |
| Sleep | Off | 7.02mA |
| Deep Sleep | On | 11.57mA |
| Deep Sleep | Off | 58.99uA |
For more information about these measurements check out this document
The wakeup source can be one of the deep-sleep enabled wakeup pins, and an RTC Alarm. You can select multiple pins and the RTC alarm to wake up the board.
This feature can be used when you want to wake up the board from external stimuli, such as sensors or user input. Some sensors have an interrupt pin that you can connect to one of the wakeup pins (eg: most motion sensors), while some output voltage on a pin, (eg: Passive Infrared Sensors or user buttons).
To select a wakeup pin just call lowPower.setWakeupPin(<pin_number>, <direction>). The direction can be either RISING if you want to wake up when voltage is applied to a pin, or FALLING if you want to wake when no voltage is applied anymore.
Here is a list of the usable interrupts:
| Arduino Pin | MCU PIN | IRQ |
|---|---|---|
| A0 | P006 | IRQ11 |
| A1 | P005 | IRQ10 |
| A2 | P004 | IRQ9 |
| A3 | P002 | IRQ8 |
| A4 | P001 | IRQ7 |
| A5 | P015 | IRQ13 |
| D4 | P401 | IRQ5 |
| D7 | P402 | IRQ4 |
Important
Not all IRQs are created equal, the number of the IRQ represents it's priority. (IRQ0 being the highest priority and IRQ15 the lowest). Be careful when selecting your IRQ pin to make sure the board behaves as expected.
This feature is particularly useful when you want to set the board to wake up at specific times. You can use this in conjunction with the RTC library.
To make your board wake up on an RTC alarm you simply need to call lowPower.setWakeupRTC() and it will enable that functionality. Check out this example for more details about setting up the RTC.
Use lowPower.sleep() for Sleep Mode and lowPower.deepSleep() for Deep Sleep Mode. Upon calling these methods the board will sleep until one of the wakeup events mentioned earlier arises.
For more information about this library check the API Reference