RadioSonde/libraries/SD/examples/NonBlockingWrite/NonBlockingWrite.ino
2022-08-24 08:28:06 +02:00

92 lines
2.2 KiB
C++
Executable File

/*
Non-blocking Write
This example demonstrates how to perform non-blocking writes
to a file on a SD card. The file will contain the current millis()
value every 10ms. If the SD card is busy, the data will be buffered
in order to not block the sketch.
NOTE: myFile.availableForWrite() will automatically sync the
file contents as needed. You may lose some unsynced data
still if myFile.sync() or myFile.close() is not called.
The circuit:
- Arduino MKR Zero board
- micro SD card attached
This example code is in the public domain.
*/
#include <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() {
Serial.begin(9600);
while (!Serial);
// 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 10 ms since the last line added
unsigned long now = millis();
if ((now - lastMillis) >= 10) {
// 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);
}
}