| /* | |
| 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. | |
| */ | |
| // 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); | |
| } | |
| } | |