Complexity: medium
What do you need:
- two CC1310 LaunchPads
- Code Composer Studio
- TI RTOS
- Sensor Controller Studio
This blog digs into the sub-module that manages communication with sensors. A dedicated part of the IC that takes care that Radio and CPU can sleep until something meaningful happens in sensor land.
adapted from: ti
You'll learn how to run the system low power and let the Sensor Controller module wake up the rest of the CC1310 only when needed.
In part 2, we look at the TI-RTOS integration between the Engine, ARM core and radio or the CC1310 controller. |
Sensor Controller Engine: WSN Node example (cont.)
In the previous post, I looked at the Sensor Controller Engine (SCE) in isolation. I used the Studio and configured the SCE to sample a single ADC input.
And then the Studio talked to the SCE directly. We ran the setup code, sampled the input and showed the measurements on a graph.
This is useful in a way, because we now know that that part works. But this isn't firmware yet. We haven't integrated the sampling in an application.
That full integration is done for us in the remainder of the WSN Node example that we started to review in Part 1.
Here's a summary of what this program does, quoted from the readme file.
I've changed a few parts (in blue italic font) because our board doesn't have a light sensor.
Example SummaryThe WSN Node example illustrates how to create a Wireless Sensor Network Node device which sends packets to a concentrator. This example is meant to be used together with the WSN Concentrator example to form a one- to-many network where the nodes send messages to the concentrator.
This examples showcases the use of several Tasks, Semaphores and Events to get sensor updates and send packets with acknowledgement from the concentrator. For the radio layer, this example uses the EasyLink API which provides an easy-to-use API for the most frequently used radio operations.
Peripherals Exercised
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This is the short application structure (CM3 means ARM Cortex M3 core):
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We will ignore the Radio Task and its configurations. This blog covers that.
For this example, you just have to understand that we can tell the radio to wake up and transmit a chunk of data to a WSN concentrator.
Our focus is on the NodeTask. This TI-RTOS task does 3 main things.
- initialise the SCE and start it.
- Sleep until woken up by SCE
- Ask Radio Core to send out the SCE data.
The logic is in the nodeTaskFunction() function in NodeTask.c.
Initialise and start SCE
The core logic of the SCE has been configured in Part 1.
The startup part of our Node task (it's called Node task because we are the Node in the WSN scenario) activates that.
/* Start the SCE ADC task with 1s sample period and reacting to change in ADC value. */
SceAdc_init(0x00010000, NODE_ADCTASK_REPORTINTERVAL_FAST, NODE_ADCTASK_CHANGE_MASK);
SceAdc_registerAdcCallback(adcCallback);
SceAdc_start();
The callback function's only task is to tell us the sampled value and wake up the Cortex core when the SCE deems that neccessary:
void adcCallback(uint16_t adcValue)
{
/* Save latest value */
latestAdcValue = adcValue;
/* Post event */
Event_post(nodeEventHandle, NODE_EVENT_NEW_ADC_VALUE);
}
Sleep until woken up
In the loop of our RTOS task, we put the core to sleep. When the SCE wants to wake us up, it'll call the callback adcCallback() above.
while(1) {
/* Wait for event */
uint32_t events = Event_pend(nodeEventHandle, 0, NODE_EVENT_ALL, BIOS_WAIT_FOREVER);
Send Data over the Radio
When that callback is executed by the SCE, our ARM core wakes up the radio and communicates with the Concentrator.
/* If new ADC value, send this data */
if (events & NODE_EVENT_NEW_ADC_VALUE) {
/* Send ADC value to concentrator */
NodeRadioTask_sendAdcData(latestAdcValue);
}
}
Then we go back to the start of the while() loop and go back to sleep. This cycle runs as long as the device is turned on.
You will not be able to appreciate the low power use when you're running this via a debugger.
An attached debugger (software-attached, not just physically attached) prevents the core to go into low power mode.
Testing the WSN
Program your second LaunchPad with the WSN Concentrator example, and off you go.
If you have an LCD Boosterpack (430BOOST-SHARP96) you can mount that on the Concentrator and view the results.
Else open a terminal program to the Concentrator's serial port and check its output (115200 kbps, 8 data bits, 1 stop bit, no parity or flow control).
You don't absolutely need the Concentrator running. The Node sends data and waits for an acknowledgement from the Concentrator.
But it will happily timeout and continue its duties when you don't have a receiving counterpart to send that ACK.
Top Comments
Hi Jan,
Excellent series!!
Another great post Jan.
I really appreciate the time you are taking to make your updates clear and concise for others to follow.
DAB
Thank you!