Nano 33 BLE Rev2 processing speed as compared to Nano 33 IoT

[jdcosta]

I recently purchased a Nano 33 BLE Rev2 to replace a Nano 33 IoT for a BLE IMU project. I found that Nano 33 BLE Rev2 peripheral BLE notification for the standard twenty byte packet to the central android app to be more 50% slower than the Nano 33 IoT. I do understand the BLE Rev2 uses the nRF52840 and the IoT uses the SAMD21 Cortex®-M0+ 32bit low power ARM MCU. I would have expected the nRF52840 to have better performance as it implemented the ARM® Cortex-M4 processor and is clocked faster the SAMD21 Cortex®-M0+ 32bit low power ARM MCU.
I ran the following loop test:

unsigned long timerCounter = 0;
unsigned long lastTimerTime = millis();
float cyclesPerSecond = 1;

void setup() {
  // put your setup code here, to run once:
  //Initialize serial and wait for port to open:
  Serial.begin(115200);
}

void loop() {
  // put your main code here, to run repeatedly:
    timerCounter++;
    if (millis() - lastTimerTime > 5000) {
      cyclesPerSecond = timerCounter / 5.0;
      Serial.println("Cycles per Second: " + String(cyclesPerSecond) );
      timerCounter = 0;
      lastTimerTime = millis();
    }
}


The above code gives 82K Loop cycles/sec on the Nano 33 BLE Rev2 and 766K Loop cycles/sec on the Nano 33 IoT.
Is it expected that the Nano 33 BLE Rev2 is slower for the above loop code?  Maybe there is some configuration I didn’t do correctly.  Thanks in advance for responses.

[jdcosta]

I saw mention in another post "Nano 33 BLE is running mbed OS". So I rewrote the test script to use mbed Timer instead of the Arduino millis():

#include "mbed.h"

int timerCounter = 0;
float cyclesPerSecond = 1;

mbed::Timer t;

void setup() {
  // put your setup code here, to run once:
  //Initialize serial and wait for port to open:
  Serial.begin(115200);
  t.start();
}

void loop() {
  // put your main code here, to run repeatedly:
    timerCounter++;
    if (t.read_ms() > 5000) {
      cyclesPerSecond = timerCounter / 5.0;
      Serial.println("Cycles per Second: " + String(cyclesPerSecond) );
      timerCounter = 0;
      t.reset();
    }
}

This improved the Nano BLE rev2 cycles per second from 82K to 83.7K...an improvement, but the Nano IoT is still 766K cycles per second.