File content as of revision 1:5c9bde92518d:

#include "mbed.h"
#include "SDFileSystem.h"

SDFileSystem sd(PA_7, PA_6, PA_5, PA_4, "sd");  //mosi, miso, sck, cs

Serial pc(PA_2, PA_3);               // This is USB tx, rx
Serial sensor_uart(PA_9, PA_10);        // This is USART2 tx, rx

DigitalOut myled(PC_13);             // This is USER LED
//DigitalOut myled2(PA_7);             // This is USER LED
DigitalIn Button(PB_12);   // This is Blue-Button

#define Pressed 0
#define NotPressed 1

int USBByte='\0';
int GaugeByte='\0';
int n=0;
int readgauge = 0;
Timer t;
char buf[32];
char str[32];
char str2[32];
uint8_t writeflag = 0;
long millis = 0;

void PC_INT()  // USART2 used for Debug
{
    // Note: you need to actually read from the serial to clear the RX interrupt
    pc.putc(pc.getc());
    myled = (myled)?(0):(1);
}

void SENSOR_USART_INT()  // SENSOR_USART
{
    if (sensor_uart.getc() == 'R') {
        myled = (myled)?(0):(1);
        sprintf(str, "%d; %s;", t.read_ms(), sensor_uart.gets(buf, 5));
        writeflag = 1;
        //pc.printf("%s\r\n", str);
    }
}

int main()
{
    myled = 0;

    // SetUp the baud rate
    pc.baud(115200);
    sensor_uart.baud(9600);

    mkdir("/sd/ultrasonic", 0777);

    FILE *fp = fopen("/sd/ultrasonic/test.csv", "w");
    if(fp == NULL) {
        pc.printf("Could not open file for write\n");
    }
    fprintf(fp, "timestamp;value;");
    //fclose(fp);

    pc.printf("\n\r\n\r|||||START MAIN|||||\n\r");
    t.start();
    sensor_uart.attach(&SENSOR_USART_INT);
    pc.attach(&PC_INT);

    while(1) {
        if (Button)
            fclose(fp);
        if (writeflag) {
            memcpy(str2, str, 32);
            fprintf(fp, "%s\n", str2);
            writeflag = 0;
            fprintf(pc, "%s\r\n", str2);
        }
    }
}