Arduino uno - calculating and outputting a time for each loop to execute?

Projects Programming
1

Hi Community,

I am attaching a code which prints values of angles in degrees and rads which come from a magnetic sensor.
I was wondering how to find and serial print the time taken for a loop to execute?
This would be subtracted from the previous time taken but I am unsure on how to use the millis () function or another method to achieve this?

kind regards

unoproject

#include <SPI.h>

//Set Slave Select Pin
//MOSI, MISO, CLK are handled automatically
int CSN = 10;
int SO = 12;
int SI = 11;
int CLK = 13 ;
unsigned int angle;
int dis = 0;


void setup() {
  
  Serial.begin(115200);

  //Set Pin Modes
  pinMode(CSN, OUTPUT);
  pinMode(SI, OUTPUT);
  pinMode(SO, INPUT);
  pinMode(CLK, OUTPUT);
  //Set Slave Select High to Start i.e disable chip
  digitalWrite(CSN, HIGH);
  //Initialize SPI 
  SPI.begin();
}

void loop() {

  SPI.beginTransaction(SPISettings(10000000, MSBFIRST, SPI_MODE1));
  
  //Send the Command Frame
  digitalWrite(CSN, LOW);
  delayMicroseconds(1);
  SPI.transfer16(0xFFFF);
  digitalWrite(CSN,HIGH);

  //Read data frame
  digitalWrite(CSN, LOW);
  delayMicroseconds(1);
  angle = SPI.transfer16(0xC000);
  digitalWrite(CSN, HIGH);
  SPI.endTransaction;

  angle = (angle & (0x3FFF));
  
  int pos = ( (unsigned long) angle)*360UL/16384UL;
  int dis = (pos * (3.1415/180));
 

  
Serial.print ("Angle in degrees =\t");
Serial.print (pos);
Serial.print("\t Angle in Rads =\t");
Serial.print (dis);



  delay(1000);
  
}
2 
unsigned long start_time=millis(); //record start time
...
unsigned long delta_t = millis() - start_time; //the difference
3

I was wondering how to find and serial print the time taken for a loop to execute?

Record the value returned by "micros()" at the start of "loop()".
Record the value returned by "micros ()" at the end of "loop()" ( but before the delay).
Do some simple arithmetic on the two values, and print the result.

4

jremington:

unsigned long start_time=millis(); //record start time

...
unsigned long delta_t = millis() - start_time; //the difference

Hi jremington,

is this part of the void setup or included within the loop?

5

I was wondering how to find and serial print the time taken for a loop to execute?

You don't find it. You measure it.

It's rather pointless to talk about determining how long a process takes, in the hopes on optimizing the time, when you spend several orders of magnitude longer than that with your head stuck in the sand.

6

UnoProject:
Hi jremington,

is this part of the void setup or included within the loop?

it depends if you want to measure the time setup takes to execute, or how long setup takes to execute.

7

TolpuddleSartre:
it depends if you want to measure the time setup takes to execute, or how long setup takes to execute.

It's the time for the setup to execute before the delay until the next loop occurs.
To calculate angular velocity for example I require the calulation W=angle/t however the times that previously I coded was using the millis() function and was an accumulation of time since the start of the entire setup.

8

however the times that previously I coded was using the millis() function

Using millis() to time something that takes microseconds to execute is like using a calendar to make sure you get to work/school/home on time.

9

PaulS:
Using millis() to time something that takes microseconds to execute is like using a calendar to make sure you get to work/school/home on time.

So I changed the code from jremington to micros() instead of millis() and it outputs 4 microseconds per solution thats printed on the serial monitor. Does this sound reasonable to you guys?

10

Does this sound reasonable to you guys?

No.
You've probably done something wrong

11

TolpuddleSartre:
No.
You've probably done something wrong

Where abouts in the code?

#include <SPI.h>

//Set Slave Select Pin
//MOSI, MISO, CLK are handled automatically
int CSN = 10;
int SO = 12;
int SI = 11;
int CLK = 13 ;
unsigned int angle;
int dis = 0;


void setup() {
  
  Serial.begin(115200);

  //Set Pin Modes
  pinMode(CSN, OUTPUT);
  pinMode(SI, OUTPUT);
  pinMode(SO, INPUT);
  pinMode(CLK, OUTPUT);
  //Set Slave Select High to Start i.e disable chip
  digitalWrite(CSN, HIGH);
  //Initialize SPI 
  SPI.begin();
}

void loop() {

  SPI.beginTransaction(SPISettings(10000000, MSBFIRST, SPI_MODE1));
  
  //Send the Command Frame
  digitalWrite(CSN, LOW);
  delayMicroseconds(1);
  SPI.transfer16(0xFFFF);
  digitalWrite(CSN,HIGH);

  //Read data frame
  digitalWrite(CSN, LOW);
  delayMicroseconds(1);
  angle = SPI.transfer16(0xC000);
  digitalWrite(CSN, HIGH);
  SPI.endTransaction;

  angle = (angle & (0x3FFF));
  
  int pos = ( (unsigned long) angle)*360UL/16384UL;
  int dis = (pos * (3.1415/180));
 unsigned long start_time=micros(); //record start time
unsigned long delta_t = micros() - start_time; //the difference

  
Serial.print ("Angle in degrees =\t");
Serial.print (pos);
Serial.print("\t Angle in Rads =\t");
Serial.print (dis);
Serial.print("\t Time =\t");
Serial.println (delta_t);


  delay(500);
  
} /[code]
12

Whereabouts?

 unsigned long start_time=micros(); //record start time
unsigned long delta_t = micros() - start_time; //the difference

Right there.

See my reply 2

13

TolpuddleSartre:
Whereabouts?

 unsigned long start_time=micros(); //record start time

unsigned long delta_t = micros() - start_time; //the difference


Right there.

See my reply 2

So how do I go about changing this to match your first reply which was to record values of micros at start and end of loop?

14

Record the start time before the first part of the code you want to time, and record the end time after the last part of the code you want to time.

You don't time a race by firing the gun, starting the stopwatch and then immediately stopping the stopwatch.