IoT Design with Cypress PSoC® 6 MCUs and Wi-Fi/Bluetooth using Arm® Mbed™

You can “mbed import https://github.com/iotexpert/mouser-mbed-09.git“ to make a copy of the project in your workspace.

The final architecture of the thermostat looks like this.

 

Summary

I don’t know about you guys, but it annoys me every time I see that the clock isn’t set.  In this lesson we will start the IoT-ifying of this system by attaching it to WiFi and getting the network time.

Inside of the PSoC is a RealTime clock that is driven by the crystal oscillator on the board.  However, “What time is it?”  turns out to be a pretty simple question to answer if you are attached to the network.  You find out using an NTP server.  This lesson will attach to WiFi, and then every 5 minutes go get the UTC time from an NTP server.

To implement this I will

1. Import lesson05
2. Add the NTP Server Library
3. Create & Code ntpThread.h
4. Create & Code ntpThread.cpp
5. Update main.cpp
6. Build, Program and Test

Import lesson05

First import the Lesson 05 to create a new project.

https://github.com/iotexpert/mouser-mbed-05.git

Add the NTP Server Library

For this lesson I will use a library that knows how to talk to an NTP server using a TCP socket.  To get this library click on the libraries tab and press “+”

Now provide the path to the library.

https://github.com/ARMmbed/ntp-client

Use the master branch:

Create & Code ntpThread.h

As always I am going to run the NTP Client in a thread.  This thread will be called “ntpThread”:

There is nothing to this but the function definition:

#ifndef NTP_THREAD_H
#define NTP_THREAD_H
void ntpThread();

#endif

Create & Code ntpThread.cpp

Next create the actual thread code:

This code will need to include the ntp-client library.  Then I do something semi-evil by making an external reference to the WiFiInterface which will be declared in main.cpp.

Finally I will poll the NTP server every 5 minutes.  Notice that if the thing fails it tries again in 10 seconds.  When I get the time I write it into the RTC using the standard-C set_time function.  This function was connected by Cypress to the RTC hardware in the PSoC 6.

#include "mbed.h"
#include "ntp-client/NTPClient.h"

extern WiFiInterface *wifi;


void ntpThread()
{
    NTPClient ntpclient(wifi);
 
    uint32_t sleepTime = 1000 * 60 * 5 ; // 5 minutes
    while(1)
    {

        if(wifi->get_connection_status() == NSAPI_STATUS_GLOBAL_UP)
        {
            time_t timestamp = ntpclient.get_timestamp();
            if (timestamp < 0) {
                sleepTime = 1000 * 10 ; // 10 seconds
            } 
            else 
            {
                set_time(timestamp);
                sleepTime = 1000 * 60 * 5 ; // 5 minutes

            }
        }
        ThisThread::sleep_for(sleepTime); // Goto the NTP server every 5 minutes
    }
}

Update main.cpp

Now I need to update main.cpp.  This time is a little bit different since I need to setup a connection to the WiFi network.  I start by getting a pointer to the WiFi in the system and then connecting before I start all of the threads.

Notice that I hard-coded the SSID and Password.  I also try again until I have a WiFi connection.

The rest of main.cpp is normal.

#include "mbed.h"
#include "blinkThread.h"
#include "displayThread.h"
#include "temperatureThread.h"
#include "capsenseThread.h"
#include "ntpThread.h"

Thread blinkThreadHandle;
Thread displayThreadHandle;
Thread temperatureThreadHandle;
Thread capsenseThreadHandle;
Thread ntpThreadHandle;

WiFiInterface *wifi;

int main()
{

    printf("Started System\n");

    int ret;
    wifi = WiFiInterface::get_default_instance();

    do {
            ret = wifi->connect("CYFI_IOT_EXT", "cypresswicedwifi101", NSAPI_SECURITY_WPA_WPA2);
            if (ret != 0) {
            ThisThread::sleep_for(2000); // If for some reason it doesnt work wait 2s and try again
            }
    } while(ret !=0);


    ntpThreadHandle.start(ntpThread);
    blinkThreadHandle.start(blinkThread);
    displayThreadHandle.start(displayThread);
    temperatureThreadHandle.start(temperatureThread);
    capsenseThreadHandle.start(capsenseThread);
    
}

Build, Program and Test

Now when I program this version, after 10 seconds or so, my time is updated… how cool is that?