Have you ever measured the frequency of your main loop?

[badrequest]

I was just curious about how fast my main loop is looping. I thought I could maybe add digitalWrite(4, !digitalRead(4)); to my loop and measure the oscillation on pin 4. I get about 2.9 KHz, dropping briefly to about 1.8 KHz every five seconds (every five seconds it has something extra to do. This is on an LGT8F328P with the clock speed set to 1 Mhz to save power. I haven't finished my sketch yet; it will be a fair bit slower when finished. There's no real point to this post; I just wondered how fast it was looping and was pleased that my effort to measure it seemed to work.

[LarryD]

void loop()
{
SerialPrnt(micros());

}

You can do some math . . .

---

UNO
If you have scope something like this can be used:

Share tips you have come across

If you have access to a Logic Analyzer or a Storage Oscilloscope, you can use them to time events when troubleshooting your code. A write to pin D13 on the Arduino using the PINB command, toggles that pin’s state. Toggle: if the pin was ON it goes OFF, if it was OFF it goes ON. examples: PINB = 0x20 // Toggle D13 ATMEGA 328 PINB = 0x80 // Toggle D13 ATMEGA 1284 or the ATMEGA 2560 Having two of these commands in a row gives a pulse of ~62.5ns (nano seconds) for 16Mhz clocks. Creating a pul…

[badrequest]

Thanks. I get a much, much different answer with micros(). Here's a table with some of the values I took from the serial monitor. Did I do the calculations wrong? People are gonna laugh at my slow loop. If it really is ~10 Hz, I should be able to see LEDBUILT_IN flashing if I toggle it as well. Edit: the LED just seems to be on constantly except for the interuptions every 5 seconds. It does however look flickery if viewed from my peripheral vision. If I can sense it flickering, it must at least be closer to 10 Hz than 2.9 KHz. The extra serial prints must have slowed it down a bit but I don't know how much. Edit: it's now 43.8 Hz according to my multimeter. It shoots back up to 1.8/1.0 KHz when I remove the serial print and 2.8/1.7 KHz when I remove the LED blink. By the same virtue, toggling pin 4 must also be slowing it down a bit but I've nothing to measure otherwise.

microS	difference in us	difference in s	Hz
8613184	9408	0.09408	10.6292517006803
8622592	9344	0.09344	10.7020547945205
8631936	9344	0.09344	10.7020547945205
8641280	9408	0.09408	10.6292517006803
8650688	9344	0.09344	10.7020547945205
8660032
90000640	10432	0.10432	9.58588957055215
90011072	10432	0.10432	9.58588957055215
90021504	10368	0.10368	9.64506172839506
90031872	10432	0.10432	9.58588957055215
90042304	10432	0.10432	9.58588957055215
90052736	10432	0.10432	9.58588957055215
90063168

Unfortunately, I don't own an oscilloscope or logic analyzer.

[LarryD]

Keep in mind Serial needs time to print the values.

Speed things up by increasing the baud rate to 115200.

---

The 1.13us in my image is the time from the closing brace to the starting brace in loop()

---

We are talking about µs

[westfw]

Using a scope, I get about 150kHz for:

void setup() {
  pinMode(2, OUTPUT);
}

void loop() {
  static uint8_t out = 0;
  out = !out;
  digitalWrite(2, out);
}

(on an Uno at 16MHz. About 350kHz on a Nano Every (also at 16MHz)(!))

That's pretty consistent with the known "slowness" of digitalWrite() - your initial example has the digitalRead() in there as well, which will slow things down even more.

Note that digitalWrite() speed is somewhat dependent on exactly which pin you are using...

See also Arduino toggle speed

[Grumpy_Mike]

@badrequest

I get a much, much different answer with micros().

Micros only increment in steps of 4, not steps of 1.

[flashko]

I was curious and since I also have LGT8F328P I decided to try. The tests are at an operating frequency of 32 MHz.

#define FAST

void setup ()
{
  pinMode ( D4, OUTPUT );
}

void loop ()
{
  #ifdef FAST
  fastioWrite ( D4, HIGH );
  fastioWrite ( D4, LOW );
  #else
  digitalWrite ( D4, HIGH );
  digitalWrite ( D4, LOW );
  #endif
}

Without FAST:
Sketch uses 874 bytes (2%) of program storage space. Maximum is 29696 bytes.
Global variables use 9 bytes of dynamic memory.
352 kHz

With FAST:
Sketch uses 646 bytes (2%) of program storage space. Maximum is 29696 bytes.
Global variables use 9 bytes of dynamic memory.
6.4 MHz

[PerryBebbington]

@badrequest
I use this and similar to check loop speeds, to check how long a function takes to execute, to check that it does execute and all sorts of other things. The basic idea you are using can be extended to to check for lots of things. It can be a useful alternative to Serial.print for testing.

[tom321]

I am using LED in the middle and on the end of the loop.

void setup() {
  
  pinMode(LED_BUILTIN, OUTPUT);

}

void loop() {
   VRMS = (Voltage3 / 2.0) * 0.707; //root 2 is 0.707
  AmpsRMS = (VRMS * 1000) / mVperAmp;

  voltage = readVoltage();
  voltageString = String(voltage, 2);
  stringLength = voltageString.length();
  displayVoltage(stringLength);

  voltage2 = readVoltage2();
  voltageString2 = String(voltage2, 2);
  displayVoltage(stringLength);
  
//+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
digitalWrite(LED_BUILTIN, HIGH); 
//+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

  voltage3 = UzValue();
  voltageString3 = String(voltage3, 2);
  displayVoltage(stringLength3);

  // amp, phase
  voltage4 = readVoltage4();
  voltage5 = readVoltage5();

  ampString = String(voltage4, 0);
  shiftString = String(voltage5, 0);
  stringLength4 = voltageString4.length();
  displayVoltage(stringLength4);y:
  
//+++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 digitalWrite(LED_BUILTIN, LOW);  
 //++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
}