How to schedule events and tasks at particular time intervals

[Adeel]

Hi Dev Team,

I am running a program that takes in sensor data at 10 min intervals and publishes it to my server through MQTT at 1hr intervals.

I have different threads running for different events (Taking data from sensor and sending data outside). I am using the kernel timers to execute these events repeatedly.

Now, I want to schedule these events in such a way that I start my program at any time and then it reads the sensor value at 00:00 (12 am), 00:10 (12:10)... with 10 mins interval and then publishes my sensor value to server through MQTT every 1 hour (01:00, 02:00....) at exact times. 

Currently, I just start the program and then the process initiates at that time and continues. But I need the data to be read at specific times i.e: start of the hour time (like exactly at 12:00,12:10, 12:20, 12:30, 12:40, 12:50, 01:00) and then publish the data exactly at 01:00,02:00,03:00... and then continue this process.

Could you let me know how to schedule events such that they happen sequentially at the time I need.

Regards,

Adeel. 

[Adeel]

Just an addition that I forgot, my hardware is a: Thingy91 v1.4.0 . 

[Carl Richard]

Hi, Adeel!

You can sample the current time using the Date-Time library of NCS. If you do this on startup, after connecting to LTE, you can start a timer based on the time you get or alternatively submit a delayed work item. 

Best regards,
Carl Richard

[Adeel]

Hi Carl,

I am using the date_time library to get the real time using the NTP server. 

Can you let me know how can I use this time to synchronize my next intervals.

For example, my sample starts at 17:02:09 and I want my next interval of sending data over MQTT to occur at 18:00:00. 

For some reason, even if my application sample starts at 17:25:34 , still I want it to send the first data at 18:00:00 . 

Once I send the data for the first time, then I understand that the kernel timers can schedule it as per our timer allotment.

How can I schedule events like this because the kernel timers are defined for fixed intervals ? 

Ex: k_timer_start(&my_connect_timer, K_SECONDS(60), K_SECONDS(3600)); // To send data every hour but the start of the sample and my intervals don't match now. My sample starts at 17:25:34 and I need to synchronize it to send the first data at 18:00:00. Could you help me explain how tis could be done ? 

Regards,

Adeel.

[Carl Richard]

Hi, Adeel!

I suggest that you do the following procedure:
1. Start up, connect and get current time
2. Submit a delayed work item as described in the documentation. You can calculate the delay by converting to human readable time (see the attached code) and calculating how much time is left to, for example, the next whole hour. 
3. You can then avoid doing this again by starting a timer with the work item that makes the device transmit at the desired interval afterwards. Note that it may drift over time, so you should calibrate after a certain amount of uploads.

Delay calculation code below:

//Get timestamp
int64_t curr_time;
date_time_now(&curr_time);

int64_t curr_time_s = curr_time/1000;   			//Convert to seconds
struct tm * readable_time = gmtime(&(curr_time_s)); //Get human readable time with time.h
LOG_INF("Curr min: %d", readable_time->tm_min);
LOG_INF("Curr sec: %d", readable_time->tm_sec);

int delay = 3600-(readable_time->tm_min)*60 - readable_time->tm_sec;

This requires the time.h library. I hope it makes sense!

Best regards,
Carl Richard

[Adeel]

Hi Carl,

Yes, I understood the logic of calculating the delay and this is what I needed.

Thanks a lot, got it working at my end through the delayed work queue :).

Regards,

Adeel.