At the beginning of the list of functionalities that will get disrupted is the PWM which is also dependent on the hardware timer. However, forcing a hard reset to the hardware timer used by the millis() function will mess up a lot of the internal Arduino core functionalities. And you can explicitly cast the subtraction result to protect your code against this issue. I’ve read online that somebody is trying to reset the hardware timer for millis() in order to prevent the millis() overflow (rollover) issue.Īs we’ve stated in the previous section, even when it happens, the millis() overflow (rollover) will not disrupt the timing or logical behavior of your system. There is no need to do a reset for the Arduino millis() function’s counter. If ( ( unsigned long ) ( T2 - T1 ) >= TimeInterval ) Which recreates the overflow scenario and prints the result that we were afraid it’d be messed up. And you can test this overflow situation on your own without waiting for 50 days by using the code example below. Therefore, there is no need to worry about this issue at all because even when it happens, it won’t disrupt the logical or timing behavior of your system. However, as we’re using unsigned numbers for both variables and the result is also an unsigned number, the subtraction will give the absolute difference between (T2 & T1). In this case, T2 is no longer larger than T1, and doing the subtraction ( T2 – T1) is expected to result in a huge negative number. However, at the overflow time, the T1 will have something like (4,294,967, 280) and T2 has passed the (4,294,967, 295) limit and rolled back to zero and now has a value of 84. And your application will keep running smoothly and toggle the LED every TimeInterval as you’ve programmed it to. Here is the full code listing for this example.Īlways T2 (the current time stamp) will be larger than T1 (the previous timestamp). This example project is acting more like a simple scheduler’s dispatcher in my opinion. You can build on top of this example and create a simple small scheduler. There is no strong reasoning behind choosing those actions for the 3 tasks specifically, I just wanted to demonstrate how to attempt multitasking on Arduino using the millis function. Task 3: executes every 200ms, and it sends the button state to the PC over the serial port.Task 2: executes every 25ms, reads an input button (pin4), debounces it, and turns ON an LED output (pin5) while the button is pressed.Task 1: executes every 70ms, and it toggles the built-in LED (pin13). We’ll have 3 tasks in this example project, each of which has its own periodicity and a certain logic to execute (task handler function. We’ll use the Arduino millis() function to achieve multitasking and execute different tasks at different periodicities. This is a little bit more complex project than the previous example. As shown on my oscilloscope scene, it’s a clean 100ms time interval for the LED pin toggle event. Here is the result of testing this project on my Arduino UNO board. You can check this simulation project on TinkerCAD using this link. You can run it as is, or make a copy and add your own code and start running the simulation to see how it’s going to behave. Here is the simulation result for this project on the TinkerCAD simulator. In this way, we’ve achieved the same functionality of a delay without even using a delay that blocks the CPU for no reason and also we’re using an efficient way that’s easily scalable for larger systems as we’ll see in the next project example.
0 Comments
Leave a Reply. |