Arduino floating point test

 

How to choose the Arduino MCU for fast and double precision data processing

Giovanni Carrera, 19/02/2025

In my case I had to convert in real time the coordinates of a GNSS RTK receiver from degrees and minutes to degrees with at least 7-8 decimal places to have a resolution lower than a centimeter. So it was necessary to use double precision calculations. To do this I initially used an Arduino Due board with a program developed with Arduino IDE. Then I used other 32-bit MCUs because the 8-bit ones accept double precision but do the calculations in single. I also discarded the development in MicroPython because, at the moment, it uses single precision.

I then wrote the following program and, with minor modifications (serial UART), ran it on several 32-bit MCUs. All of the ones listed here gave identical results, but with very different execution times.

The program is as follows:

/* program doubletest.ino

 test double precision of MCU

 Giovanni Carrera, 14/10/2019*/

 

const String Lats = "4221.0081996";

const String Longs = "01321.4740622";

 

void setup(void) {

  Serial.begin(115200);

     while (!Serial) {

    ; // wait for serial port to connect

  }

  delay(100);

  Serial.println("MCU double precision test");

  // convert Lat&Long in decimal format

  unsigned long  ti= micros();

  String minuts = Lats.substring(2);// latitude minutes

  double minutes = minuts.toFloat();// convert it to float

  double decdeg = minutes/60.0;

  String Latdegs = Lats.substring(0,2);

  double Latd = Latdegs.toFloat() + decdeg;// latitude in decimal format (double)

  minuts = Longs.substring(3);// longitude minutes

  minutes = minuts.toFloat();// convert it to float

  decdeg = minutes/60.0;

  String Longdegs = Longs.substring(0,3);

  double Longd = Longdegs.toFloat() + decdeg;// longitude in decimal format (double)

  unsigned long  tf= micros();

  Serial.print("Latitude (dec)  = ");

  Serial.println(Latd,8);

  Serial.print("Longitude (dec) = ");

  Serial.println(Longd,8);

  Serial.print("elaboration time [us] = ");

  Serial.println(tf-ti);

} // end of setup

 

 

void loop() {

}

The following table summarizes the results of my tests.

board	MCU	CPU clock [MHz]	time [µs]
Teensy 4.0	ARM Cortex-M7	600	5
Arduino Due	Atmel SAM3X8E ARM Cortex-M3	84	141
ESP32 WROOM	Xtensa single-/dual-core 32-bit LX6	240	152
STM32F103C8T6	ARM Cortex-M3	72	157
Arduino Uno R4	ARM Cortex-M4	48	184
Arduino Zero	ATSAMD21G18	48	250
Wemos D1 mini	ESP8266EX, Tensilica L106	80	388

The graphic representation of the figure shows the differences better.