Program slower with 3.2 clock in overdrive than with non-overdrive clock

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amundsen

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Hello,

I am running the program below on an Teensy 3.2 connected to a Pozyx tag shield.

When running the board at 72 MHz, I get dt oscillating between 26 and 27 ms. However when running it at 96 MHz, dt is steady at 28 ms, while at 120 MHz it oscillates between 27 and 28 ms. How come that a faster clock causes a slower response? It is becaue of the Pozyx lib or hardware?
 
I think the main thing controlling the speed, is that I believe this device communicates using I2C (Wire library). And I believe it runs with the default clock of 100000.
So it will be more or less the same regardless of how fast the teensy runs.

The interesting thing is when you run at 96mhz, the F_BUS is set to 48mhz, and for request of 100K, the actual Wire speed is 100KHz

At 72mhz, the F_BUS is 36MHz and the the actual frequency for < 40000 is 113KHz so it runs faster than the requested speed... And so if your programs timings are dictated by reading the device over wire the slower speed is faster.

And note: at 120MHZ -> 60Mhz -> 104KHz so faster than 96 but slower than 72...
 
Thank you, KurtE!

By the way, I forgot to post the code. Here it is:
Code: 
/**
  The pozyx ranging demo (c) Pozyx Labs
  please check out https://www.pozyx.io/Documentation/Tutorials/getting_started/Arduino
  
  This demo requires one (or two) pozyx shields and one Arduino. It demonstrates the 3D orientation and the functionality
  to remotely read register data from a pozyx device. Place one of the pozyx shields on the Arduino and upload this sketch. 
  
  This demo reads the following sensor data: 
  - pressure
  - acceleration
  - magnetic field strength
  - angular velocity
  - the heading, roll and pitch
  - the quaternion rotation describing the 3D orientation of the device. This can be used to transform from the body coordinate system to the world coordinate system.
  - the linear acceleration (the acceleration excluding gravity)
  - the gravitational vector
  
  The data can be viewed in the Processing sketch orientation_3D.pde 

  Tested successfully with Teensy 3.2 with modified interrupts in Pozyx lib
  
*/

#include <Pozyx.h>
#include <Pozyx_definitions.h>
#include <Wire.h>

////////////////////////////////////////////////
////////////////// PARAMETERS //////////////////
////////////////////////////////////////////////

boolean remote = true;               // boolean to indicate if we want to read sensor data from the attached pozyx shield (value 0) or from a remote pozyx device (value 1)
uint16_t remote_id = 0x6e6a;          // the network id of the other pozyx device: fill in the network id of the other device
uint32_t last_millis;                 // used to compute the measurement interval in milliseconds 

////////////////////////////////////////////////

void setup()
{  
  Serial.begin(115200);
  Serial.println("Setup started.");
    
  if(Pozyx.begin(false, MODE_INTERRUPT, POZYX_INT_MASK_IMU) == POZYX_FAILURE){
    Serial.println("ERROR: Unable to connect to POZYX shield");
    Serial.println("Reset required");
    delay(100);
    abort();
  }

  if(!remote)
    remote_id = NULL;
  
  last_millis = millis();
  delay(10);  
  Serial.println("Setup finished.");
}

void loop(){
  sensor_raw_t sensor_raw;
  uint8_t calibration_status = 0;
  int dt;
  int status;
  if(remote){
     status = Pozyx.getRawSensorData(&sensor_raw, remote_id);
     status &= Pozyx.getCalibrationStatus(&calibration_status, remote_id);
    if(status != POZYX_SUCCESS){
      return;
    }
  }else{
    if (Pozyx.waitForFlag(POZYX_INT_STATUS_IMU, 10) == POZYX_SUCCESS){
      Pozyx.getRawSensorData(&sensor_raw);
      Pozyx.getCalibrationStatus(&calibration_status);
    }else{
      uint8_t interrupt_status = 0;
      Pozyx.getInterruptStatus(&interrupt_status);
      return;
    }
  }

  dt = millis() - last_millis;
  last_millis += dt;    
  // print time difference between last measurement in ms, sensor data, and calibration data
  Serial.print("dt: ");
  Serial.print(dt, DEC);
  Serial.print(",");
  printRawSensorData(sensor_raw);
  //Serial.print(",");
  // will be zeros for remote devices as unavailable remotely.
  //printCalibrationStatus(calibration_status);
  Serial.println();
}

void printRawSensorData(sensor_raw_t sensor_raw){
  //Serial.print(sensor_raw.pressure);
  //Serial.print(",");
  //Serial.print(sensor_raw.acceleration[0]);
  //Serial.print(",");
  //Serial.print(sensor_raw.acceleration[1]);
  //Serial.print(",");
  //Serial.print(sensor_raw.acceleration[2]);
  //Serial.print(",");
  //Serial.print(sensor_raw.magnetic[0]);
  //Serial.print(",");
  //Serial.print(sensor_raw.magnetic[1]);
  //Serial.print(",");
  //Serial.print(sensor_raw.magnetic[2]);
  //Serial.print(",");
  //Serial.print(sensor_raw.angular_vel[0]);
  //Serial.print(",");
  //Serial.print(sensor_raw.angular_vel[1]);
  //Serial.print(",");
  //Serial.print(sensor_raw.angular_vel[2]);
  //Serial.print(",");
  //Serial.print(sensor_raw.euler_angles[0]);
  //Serial.print(",");
  //Serial.print(sensor_raw.euler_angles[1]);
  //Serial.print(",");
  //Serial.print(sensor_raw.euler_angles[2]);
  Serial.print(", quat_0: ");
  Serial.print(sensor_raw.quaternion[0]);
  Serial.print(", quat_1: ");
  Serial.print(sensor_raw.quaternion[1]);
  Serial.print(", quat_2: ");
  Serial.print(sensor_raw.quaternion[2]);
  Serial.print(",  quat_3: ");
  Serial.print(sensor_raw.quaternion[3]);
  //Serial.print(",");
  //Serial.print(sensor_raw.linear_acceleration[0]);
  //Serial.print(",");
  //Serial.print(sensor_raw.linear_acceleration[1]);
  //Serial.print(",");
  //Serial.print(sensor_raw.linear_acceleration[2]);
  //Serial.print(",");
  //Serial.print(sensor_raw.gravity_vector[0]);
  //Serial.print(",");
  //Serial.print(sensor_raw.gravity_vector[1]);
  //Serial.print(",");
  //Serial.print(sensor_raw.gravity_vector[2]);
  //Serial.print(", temp_c: ");
  //Serial.print(sensor_raw.temperature);
}

void printCalibrationStatus(uint8_t calibration_status){
  Serial.print(calibration_status & 0x03);
  Serial.print(",");
  Serial.print((calibration_status & 0x0C) >> 2);
  Serial.print(",");
  Serial.print((calibration_status & 0x30) >> 4);
  Serial.print(",");
  Serial.print((calibration_status & 0xC0) >> 6);  
}
 
PaulStoffregen said:
Try adding this after Pozyx.begin()

Code: 
Wire.setClock(400000);
Click to expand...

Thank you for the idea, Paul! This reduced ds to 19/20 ms.

I could go down to 17/18 ms by setting the clock to 160000. I couldn't reach shorter times. My goal is to go below 10ms but I guess this would imply optimizing the Pozyx lib itself?
 
Using the Pozyx board's UWB settings in parallel with I2C rate change (1600000, not 160000 as written in my previous post), I could go down to 6ms.
 
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