Teensy 4.0 Clockspeed (iMX RT1062)

T4Clockspeed.ino

/*
 * Clock speed changes
 * Lifted from:
 * https://forum.pjrc.com/threads/57444-How-to-change-clock-speed-on-Teensy-4-0?p=214257&viewfull=1#post214257
 */

#if defined(__IMXRT1062__)
extern "C" uint32_t set_arm_clock(uint32_t frequency);
#endif

uint32_t count, prior_count;
uint32_t prior_msec;
uint32_t count_per_second;

bool flip = true;
void setup() {
#if defined(__IMXRT1062__)
    set_arm_clock(24000000);
#endif
  Serial.begin(1000000); // edit for highest baud your board can use
  while (!Serial) ;
#if defined(__IMXRT1062__)
    //set_arm_clock(24000000);
    Serial.print("F_CPU_ACTUAL=");
    Serial.println(F_CPU_ACTUAL);
#endif
  count = 10000000; // starting with 8 digits gives consistent chars/line
  prior_count = count;
  count_per_second = 0;
  prior_msec = millis();
  pinMode( LED_BUILTIN, OUTPUT );
  digitalWriteFast( LED_BUILTIN, flip );
}

void loop() {
  while (1) {
    Serial.print(" >count=");
    Serial.print(count);
    Serial.print(", lines/s=");
    Serial.print(count_per_second);
    if ( !(count % 4) ) {
      Serial.print(' ');
      Serial.println(millis() / 1000);
    }
    count = count + 1;
    uint32_t msec = millis();
    if (msec - prior_msec > 1000) {
      flip = !flip;
      digitalWriteFast( LED_BUILTIN, flip );
      if ( !Serial ) {
        delay( 50 );
        flip = !flip;
        digitalWriteFast( LED_BUILTIN, flip );
      }
      prior_msec = prior_msec + 1000;
      count_per_second = count - prior_count;
      prior_count = count;
    }
  }
}