Teensy4.1 SD CARD Writing Speed

Datalogger_Teensy4.1_Speed.ino

/*
  SD card datalogger
 
 This example shows how to log data from three analog sensors
 to an SD card using the SD library.
 	
 The circuit:
 * analog sensors on analog ins 0, 1, and 2
 * SD card attached to SPI bus as follows:
 ** MOSI - pin 11, pin 7 on Teensy with audio board
 ** MISO - pin 12
 ** CLK - pin 13, pin 14 on Teensy with audio board
 ** CS - pin 4,  pin 10 on Teensy with audio board
 
 created  24 Nov 2010
 modified 9 Apr 2012
 by Tom Igoe
 
 This example code is in the public domain.
 */

#include <SD.h>
#include <SPI.h>

// On the Ethernet Shield, CS is pin 4. Note that even if it's not
// used as the CS pin, the hardware CS pin (10 on most Arduino boards,
// 53 on the Mega) must be left as an output or the SD library
// functions will not work.

// change this to match your SD shield or module;
// Arduino Ethernet shield: pin 4
// Adafruit SD shields and modules: pin 10
// Sparkfun SD shield: pin 8
// Teensy audio board: pin 10
// Teensy 3.5 & 3.6 & 4.1 on-board: BUILTIN_SDCARD
// Wiz820+SD board: pin 4
// Teensy 2.0: pin 0
// Teensy++ 2.0: pin 20
const int chipSelect =BUILTIN_SDCARD;// 10;
 int i;
 int n;
 int num=1000;
 String dataString,dataString1;
void setup()
{
  //UNCOMMENT THESE TWO LINES FOR TEENSY AUDIO BOARD:
  //SPI.setMOSI(7);  // Audio shield has MOSI on pin 7
  //SPI.setSCK(14);  // Audio shield has SCK on pin 14
 
  // Open serial communications and wait for port to open:
  Serial.begin(9600);
  while (!Serial) {
    ; // wait for serial port to connect.
  }


  Serial.print("Initializing SD card...");

  // see if the card is present and can be initialized:
  if (!SD.begin(chipSelect)) {
    Serial.println("Card failed, or not present");
    while (1) {
      // No SD card, so don't do anything more - stay stuck here
    }
  }
  Serial.println("card initialized.");
  dataString = "";
  for(i=0;i<num;i++){
    dataString += String(i);
      dataString += ",";
  }
  
}

void loop()
{
   // open the file.
  
  File dataFile = SD.open("data_log.txt", FILE_WRITE);
  while(n<1000){
   n++;
  // if the file is available, write to it:
  if (dataFile) {
    dataString1=dataString+String(millis());
    dataFile.println(dataString1);
   
    // print to the serial port too:
    
  } else {
    // if the file isn't open, pop up an error:
    Serial.println("error opening datalog.txt");
  }
  //delay(1); // run at a reasonable not-too-fast speed
  }//n<1000
   dataFile.close();
  Serial.println("-------SD Write Finished");
  exit(0);
}