Power Management

TinyCLR exposes several power modes for trading off responsiveness against energy consumption — useful for battery-powered devices, deep-sleep IoT nodes, and anything that needs to nap until something interesting happens.

NuGet packages: GHIElectronics.TinyCLR.Native for the Power API, plus GHIElectronics.TinyCLR.Devices.Gpio and GHIElectronics.TinyCLR.Pins when wiring wake-up interrupts.

Idle

When the runtime has nothing to do — all threads sleeping or blocked on events — the system automatically enters idle. You don't call anything; this is the default state between active work.

Slow clock speed

The CPU can run at half speed, cutting power use by about 40%. Switching requires a soft reset, and the change can optionally persist across resets.

using GHIElectronics.TinyCLR.Native;

var persistClock = false;

if (Power.GetSystemClock() == SystemClock.High) {
    Power.SetSystemClock(SystemClock.Low, persistClock);
    Power.Reset();
}

Switch back to full speed (only works if persistClock was false when you switched down):

if (Power.GetSystemClock() == SystemClock.Low) {
    Power.SetSystemClock(SystemClock.High, persist: false);
    Power.Reset();
}

When not persisted, Power.Reset() keeps the current clock speed, but a hardware reset (reset pin) or a power cycle reverts to the default.

Sleep

Sleep disables most of the system to drop power consumption substantially. A GPIO edge or the RTC can wake the device and resume execution where it left off.

note

You must register an interrupt handler on the wake-up pin before calling Power.Sleep() — otherwise the system has no idea what edge to wake on.

using GHIElectronics.TinyCLR.Devices.Gpio;
using GHIElectronics.TinyCLR.Native;
using GHIElectronics.TinyCLR.Pins;
using System.Diagnostics;

var ldrButton = GpioController.GetDefault().OpenPin(SC20100.GpioPin.PE3);
ldrButton.SetDriveMode(GpioPinDriveMode.InputPullUp);
ldrButton.ValueChanged += LdrButton_ValueChanged;

Debug.WriteLine("Going to sleep...");
Power.Sleep();
Debug.WriteLine("Woken up");

// Handler can be empty — its existence is what arms the interrupt for wake-up.
void LdrButton_ValueChanged(GpioPin sender, GpioPinValueChangedEventArgs e) { }

Sleep for a specific time using the RTC:

Power.Sleep(DateTime.Now.AddSeconds(90));    // Wake in 90 seconds.

Shutdown

The deepest power state. The system is completely off, internal pull-ups are disabled, and the only ways to wake it are:

• A reset
• A power cycle
• The RTC alarm firing
• A configured edge on the WKUP pin

warning

Waking from Shutdown always resets the system. Your application starts over from scratch — it doesn't resume where it left off. Anything you need across the sleep has to live in battery-backed memory or external storage.

note

Internal pull-ups are off in Shutdown, so add an external pull-up or pull-down to the WKUP pin to give it a stable default state — otherwise spurious wake-ups are possible.

Shutdown until WKUP changes:

Power.Shutdown(true, DateTime.MaxValue);

By default the system wakes on a rising edge of WKUP. Switch to falling edge:

Power.WakeupEdge = WakeupEdge.Falling;

Shutdown for a fixed time (WKUP pin ignored):

Power.Shutdown(false, DateTime.Now.AddSeconds(90));

Shutdown for a fixed time or until WKUP changes (whichever comes first):

Power.Shutdown(true, DateTime.Now.AddSeconds(90));

Disabling on-board Ethernet PHY

Modules with an on-board Ethernet PHY draw power even when networking isn't in use. Pulling a specific GPIO pin low disables the PHY:

Module	Disable pin
SCM20260E/D	PG3
SCM20100E	PD8

Software reset

Reset the application from code without a hardware reset:

using GHIElectronics.TinyCLR.Native;

Power.Reset();              // Reset application.
Power.Reset(false);         // Reset into GHI Bootloader mode.

The bootloader-mode reset is useful for triggering firmware updates from inside the application — for example, from an in-app "Check for updates" menu.

Identifying the previous reset cause

After boot, GetResetSource returns what triggered the last reset — useful for distinguishing a watchdog reset, a brown-out, a user reset button press, or a clean power-up.

var resetSource = Power.GetResetSource();

API reference

Namespace	Description
GHIElectronics.TinyCLR.Native	Power mode and low-power sleep classes