NonBlockingWrite.ino

/****************************************************************************************************************************
  NonBlockingWrite.ino

  For all RP2040 boads using Arduimo-mbed or arduino-pico core

  RP2040_SD is a library enable the usage of SD on RP2040-based boards

  This Library is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License
  as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

  This Library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more details.

  You should have received a copy of the GNU General Public License along with the Arduino SdFat Library.
  If not, see <http://www.gnu.org/licenses/>.

  Based on and modified from  Arduino SdFat Library (https://github.com/arduino/Arduino)

  (C) Copyright 2009 by William Greiman
  (C) Copyright 2010 SparkFun Electronics
  (C) Copyright 2021 by Khoi Hoang

  Built by Khoi Hoang https://github.com/khoih-prog/RP2040_SD
  Licensed under GPL-3.0 license
 *****************************************************************************************************************************/
/*
  SD card connection

  This example shows how to read and write data to and from an SD card file
  The circuit:
   SD card attached to SPI bus as follows:
   // Arduino-pico core
   ** MISO - pin 16
   ** MOSI - pin 19
   ** CS   - pin 17
   ** SCK  - pin 18

   // Arduino-mbed core
   ** MISO - pin 4
   ** MOSI - pin 3
   ** CS   - pin 5
   ** SCK  - pin 2
*/


#if !defined(ARDUINO_ARCH_RP2040)
  #error For RP2040 only
#endif

#if defined(ARDUINO_ARCH_MBED)

  #define PIN_SD_MOSI       PIN_SPI_MOSI
  #define PIN_SD_MISO       PIN_SPI_MISO
  #define PIN_SD_SCK        PIN_SPI_SCK
  #define PIN_SD_SS         PIN_SPI_SS

#else

  #define PIN_SD_MOSI       PIN_SPI0_MOSI
  #define PIN_SD_MISO       PIN_SPI0_MISO
  #define PIN_SD_SCK        PIN_SPI0_SCK
  #define PIN_SD_SS         PIN_SPI0_SS

#endif

#define _RP2040_SD_LOGLEVEL_       4

#include <SPI.h>
#include <RP2040_SD.h>

// file name to use for writing
const char filename[] = "demo.txt";

// File object to represent file
File txtFile;

// string to buffer output
String buffer;

unsigned long lastMillis = 0;

void setup()
{
  // Open serial communications and wait for port to open:
  Serial.begin(115200);

  while (!Serial);

  delay(1000);

#if defined(ARDUINO_ARCH_MBED)
  Serial.print("Starting SD Card NonBlockingWrite on MBED ");
#else
  Serial.print("Starting SD Card NonBlockingWrite on ");
#endif

  Serial.println(BOARD_NAME);
  Serial.println(RP2040_SD_VERSION);

  Serial.print("Initializing SD card with SS = ");
  Serial.println(PIN_SD_SS);
  Serial.print("SCK = ");
  Serial.println(PIN_SD_SCK);
  Serial.print("MOSI = ");
  Serial.println(PIN_SD_MOSI);
  Serial.print("MISO = ");
  Serial.println(PIN_SD_MISO);

  if (!SD.begin(PIN_SD_SS))
  {
    Serial.println("Initialization failed!");
    return;
  }

  Serial.println("Initialization done.");

  // reserve 1kB for String used as a buffer
  buffer.reserve(1024);

  // set LED pin to output, used to blink when writing
  pinMode(LED_BUILTIN, OUTPUT);

  // init the SD card
  if (!SD.begin())
  {
    Serial.println("Card failed, or not present");

    // don't do anything more:
    while (1);
  }

  // If you want to start from an empty file,
  // uncomment the next line:
  // SD.remove(filename);

  // try to open the file for writing
  txtFile = SD.open(filename, FILE_WRITE);

  if (!txtFile)
  {
    Serial.print("error opening ");
    Serial.println(filename);

    while (1);
  }

  // add some new lines to start
  txtFile.println();
  txtFile.println("Hello World!");
}

void loop()
{
  // check if it's been over 100 ms since the last line added
  unsigned long now = millis();

  if ((now - lastMillis) >= 100)
  {
    // add a new line to the buffer
    buffer += "Hello ";
    buffer += now;
    buffer += "\r\n";

    lastMillis = now;
  }

  // check if the SD card is available to write data without blocking
  // and if the buffered data is enough for the full chunk size
  unsigned int chunkSize = txtFile.availableForWrite();

  if (chunkSize && buffer.length() >= chunkSize)
  {
    // write to file and blink LED
    digitalWrite(LED_BUILTIN, HIGH);
    txtFile.write(buffer.c_str(), chunkSize);
    digitalWrite(LED_BUILTIN, LOW);

    // remove written data from buffer
    buffer.remove(0, chunkSize);
  }
}