RUI3-LowPower-Example

Example how to achieve lowest power consumption with a custom firmware created with RUI3

One problem often seen when writing custom code with RUI3 is that the loop() is used together with api.system.sleep.all(xxxxx). This is IMHO not the best solution to achieve lowest power consumption and brings some timing problems, as when a LoRa or LoRaWAN packet is sent, the TX finished event will wake up the system and it will not go back to sleep.

This example code is NOT using the loop at all. Instead it is complete event driven. The WisDuo/WisBlock module is sleeping unless an event occurs. An event can be a timer callback or an external interrupt, or if using LoRaWAN Class C, it can be a packet received from the LoRaWAN server.

This code does setup a timer that wakes up the device in the desired send interval, send a packet and then the system goes back to sleep automatically.
It can be extended to use external interrupts, see my other examples codes.

This examples includes two custom AT commands:

• ATC+SENDINT to set the send interval time or heart beat time. If the device is not in motion it will send a payload with this interval. The time is set in seconds, e.g. AT+SENDINT=600 sets the send interval to 600 seconds or 10 minutes.
• ATC+STATUS to get some status information from the device.

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Code sections

⚠️ INFORMATION

The code snippets below are simplified. Check the provided source code for the full code.

LoRa/LoRaWAN callbacks

There are different system callbacks that are invoked on LoRa/LoRaWAN events.

For LoRaWAN there are 3 callbacks for join, send and receive events.

LoRaWAN join event is called when a join request was successful or failed. If it fails, it is called after all retries are used up, not on each single retry. The callback has the parameter int32_t status. The status is based on low level LoRaMAC stack results, at the moment the only usuable check is whether the status is 0 ==> join success or <>0 ==> join failed. It is possible to restart the join request from this callback if the attempt failed before.

void joinCallback(int32_t status)
{
	if (status != 0)
	{
		MYLOG("JOIN-CB", "LoRaWan OTAA - join fail! \r\n");
	}
	else
	{
		MYLOG("JOIN-CB", "LoRaWan OTAA - joined! \r\n");
	}
}

LoRaWAN TX finished callback is an important callback. It tells you whether the transmission of a LoRaWAN packet is finished. It is important, because a TX finished event is waking up the device, and when using the loop() function, a sleep call should be issued AFTER the TX finished event. The callback has the parameter int32_t status. The status is based on low level LoRaMAC stack results, at the moment the only usuable check is whether the status is 0 ==> send success or <>0 ==> send failed.

void sendCallback(int32_t status)
{
	MYLOG("TX-CB", "TX status %d", status);
}

LoRaWAN RX callback is called when a data packet was received from the LoRaWAN server. The callback has as parameter a pointer to a structure with information about the received data and pointers to the payload and its length.

void receiveCallback(SERVICE_LORA_RECEIVE_T *data)
{
	MYLOG("RX-CB", "RX, port %d, DR %d, RSSI %d, SNR %d", data->Port, data->RxDatarate, data->Rssi, data->Snr);
}

LoRa P2P TX finished callback is an important callback. It tells you whether the transmission of a LoRa packet is finished. It is important, because a TX finished event is waking up the device, and when using the loop() function, a sleep call should be issued AFTER the TX finished event. The callback has the no parameters, as LoRa P2P does not have any protocol that would allow to know if the sent packet was received by another node..

void send_cb(void)
{
	MYLOG("TX-P2P-CB", "P2P TX finished");
}

LoRa P2P RX callback is called when a data packet was received from another LoRa node. The callback has as parameter a structure with information about the received data, the payload and its length.

void recv_cb(rui_lora_p2p_recv_t data)
{
	MYLOG("RX-P2P-CB", "P2P RX, RSSI %d, SNR %d", data.Rssi, data.Snr);
}

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setup() and loop()

setup() is used as known from Arduino sketches to setup the system. It is called once after reboot or power up.
There are two important parts in the setup() code.

First it checks whether the system is working in LoRaWAN mode or as a LoRa P2P mode. Depending on this, the different callbacks are setup.

	// Setup for LoRaWAN
	if (api.lorawan.nwm.get() == 1)
	{
		// Setup the callbacks for joined and send finished
		api.lorawan.registerRecvCallback(receiveCallback);
		api.lorawan.registerSendCallback(sendCallback);
		api.lorawan.registerJoinCallback(joinCallback);
	}
	else // Setup for LoRa P2P
	{
		api.lorawan.registerPRecvCallback(recv_cb);
		api.lorawan.registerPSendCallback(send_cb);
	}

Second a periodic timer is initialized to wake up the system in intervals to send a packet to the LoRaWAN server or other LoRa P2P nodes. The interval time is set with the variable custom_parameters.send_interval.

	// Create a timer.
	api.system.timer.create(RAK_TIMER_0, sensor_handler, RAK_TIMER_PERIODIC);
	if (custom_parameters.send_interval != 0)
	{
		// Start a timer.
		api.system.timer.start(RAK_TIMER_0, custom_parameters.send_interval, NULL);
	}

The loop() function does nothing beside of killing itself, which prevents that it is called frequently from the underlaying RUI3 scheduler.

void loop()
{
	api.system.scheduler.task.destroy();
}

send_handler & send_packet

This functions are where the action is happening.

send_handler is called by the timer. First, if in LoRaWAN mode, it checks whether the node has already joined the network. Then, in this example, it is just creating a dummy payload. But this can be extended for example to read data from sensors and add these values to the payload.
After the payload is ready, it calls send_packet to get the packet sent out.

void sensor_handler(void *)
{
	if (api.lorawan.nwm.get() == 1)
	{ 
		// Check if the node has joined the network
		if (!api.lorawan.njs.get())
		{
			MYLOG("UPLINK", "Not joined, skip sending");
			return;
		}
	}

	// Create payload (Cayenne LPP format for voltage)
	g_solution_data[0] = 0x01;
	g_solution_data[1] = 0x74;
	g_solution_data[2] = 0x01;
	g_solution_data[3] = 0x8c;

	// Send the packet
	send_packet();
}

send_packet is checking whether the node is in LoRaWAN or LoRa P2P mode and sends the created payload depending on the selected mode.

void send_packet(void)
{
	// Check if it is LoRaWAN
	if (api.lorawan.nwm.get() == 1)
	{
		// Send the packet
		if (api.lorawan.send(4, g_solution_data, set_fPort, g_confirmed_mode, g_confirmed_retry))
		{
			MYLOG("UPLINK", "Packet enqueued, size 4");
		}
		else
		{
			MYLOG("UPLINK", "Send failed");
		}
	}
	// It is P2P
	else
	{
		MYLOG("UPLINK", "Send packet with size 4 over P2P");
		if (api.lorawan.psend(4, g_solution_data))
		{
			MYLOG("UPLINK", "Packet enqueued");
		}
		else
		{
			MYLOG("UPLINK", "Send failed");
		}
	}
}

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Get RUI3 devices

Get a RAKwireless RUI3 WisDuo stamp module, breakout board or evaluation board from our store

Get a RAKwireless RUI3 WisBlock Core module from our store

⚠️ INFORMATION

Only the following modules are supported by RUI3:

WisDuo

• RAK3172 stamp module
• RAK3272S breakout board
• RAK3172 evaluation board
• RAK3172-SiP chip
• RAK3272-SiP breakout board
• RAK4630 stamp module
• RAK11720 stamp module
• RAK11721 breakout board

WisBlock Core

• RAK4631-R
• RAK3372
• RAK11722

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LoRa® is a registered trademark or service mark of Semtech Corporation or its affiliates.

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LoRaWAN® is a licensed mark.