Frequency of 1000 hertz and complete this process within 5 seconds.

Questions » Frequency of 1000 hertz and complete this process within 5 seconds.

9 years ago.

Hi all , I have this working code for a 3 axis accelerator. My question is how to make it at a frequency of 1000 hertz and complete this process within 5 seconds.

Thank you for your time and have a great day.

#include "mbed.h"
#include "TextLCD.h"
LocalFileSystem local("local"); 
TextLCD lcd(p24,p26,p27,p28,p29,p30); 
Serial pc(USBTX,USBRX);
Ticker in;
AnalogIn x_in(p17);
AnalogIn y_in(p18);
AnalogIn z_in(p19);


const int maxReadings = 1000;
 
float measurmentArray[maxReadings][3];
volatile int readingNumber = 0;

void update()
{        
if (readingNumber < maxReadings) {
   measurmentArray[readingNumber][0]=x_in;
   measurmentArray[readingNumber][1]=y_in;
   measurmentArray[readingNumber][2]=z_in;
   readingNumber++;}}
  
  main  () {
  int nextReading = 0;
  in.attach_us(&update,1000);//1000 hertz???
 
  while (nextReading<maxReadings ) { //process until no more space
    if (readingNumber > nextReading) { // there is new data
       nextReading = readingNumber-1; // the index of the last value written to the array
       float x,y,z;  // copy values to a local variables 
       x=measurmentArray[nextReading][0];
       y=measurmentArray[nextReading][1];
       z=measurmentArray[nextReading][2];
 
      pc.printf("X-%5.2f Y-%5.2f Z-%5.2f \n",x, y, z);
      nextReading++;
    }
  }    
  // write array in the file txt/csv
 FILE *fp = fopen("/local/Record.csv", "a");
 if (fp) {
   for (int i=0;i<maxReadings;i++) {
      
       fprintf(fp, "%f , %f , %f \r ",measurmentArray[i][0],measurmentArray[i][1],measurmentArray[i][2]);
      
    }
    fclose(fp);
  } else {
    pc.printf("ERROR. Failed to open output file\r\n");
  }
}

1 Answer

9 years ago.

Hi Sze Ming,

A couple things. First I fixed some formatting issues. The bracket placement and indenting made it hard to read. The program logic was a little hard to follow in my opinion, so I tried to clean it up. There is only one counter now that tracks what index we are on.

I think the printf output cannot happen in realtime. I think you would struggle to printf 1000 times a second. I think it is better to capture the data first, then print it at once. If you absolutely need to send data out the serial port when it is captured, I suspect that will be more work in order to optimize the time to do data conversion and send it out the serial port. I suspect printf may be too slow for this and you will have to write your own fast data conversion function. I have not tested the timing, that's just a gut feeling.

So I made a printf loop that runs after data is captured. I am using SWV channel to view the data. I am not setup right now to view data on a regular serial channel. SWV is fast, but even here I find I have to slow down the printf statements to avoid getting garbled output data. There is a 5ms wait in there. Adjust based on what works for you. I am not sure where or why the data is getting garbled. More investigation would be needed.

I added an infinite wait loop at the end of main. I think actually exiting main could cause undesirable behavior.

This is mostly working. My micro does not have a file system, so I can't test that function. The whole thing finishes for me in about 5 seconds, 1 second reading data and 4s printing data.

Good luck.

#include "mbed.h"
//#include "TextLCD.h"

/* Objects */
LocalFileSystem local("local");
Serial pc(USBTX,USBRX);
DigitalOut led(PB_14);
Ticker in;
AnalogIn x_in(p17);
AnalogIn y_in(p18);
AnalogIn z_in(p19);
//TextLCD lcd(p24,p26,p27,p28,p29,p30);



/* Variables */
const int MAX = 1000;
volatile int count = 0;
volatile float measurmentArray[MAX][3];


/*** Update ***
* Record new values in array.
* If statement guards against chance of 1 extra read.
*/
void update() {

    if (count < MAX) {

        measurmentArray[count][0] = x_in.read();
        measurmentArray[count][1] = y_in.read();
        measurmentArray[count][2] = z_in.read();

        count++;
    }
}


/*** Main ***
*/
int main  () {

    /* Temp Variables */
    float x,y,z = 0;

    /* 1000 Hz = 1000us */
    in.attach_us(&update,1000);

    /* Wait Until Full */
    while (count < MAX) {

    }

    /* Print Data */
    for (int i=0; i<MAX; i++) {
        x = measurmentArray[i][0];
        y = measurmentArray[i][1];
        z = measurmentArray[i][2];

    	pc.printf("X-%5.2f Y-%5.2f Z-%5.2f \r\n",x, y, z);

    	/* Delay may be Needed to Prevent Overloading Channel */
    	wait_ms(5);
    }

    pc.printf("--END--\r\n");

    /* Turn Interrupt Off */
    in.detach();

    /* Write array to file txt/csv */
    FILE *fp = fopen("/local/Record.csv", "a");

    if (fp) {
        for (int i=0; i<MAX; i++) {
            fprintf(fp, "%f , %f , %f \r ",measurmentArray[i][0],measurmentArray[i][1],measurmentArray[i][2]);
        }
        fclose(fp);
    }
    else {
        pc.printf("ERROR. Failed to open output file\r\n");
    }

    /* Don't Exit Main */
    while(true) {
    	led =! led;
        wait(1);
    }
}

Graham

Accepted Answer

Sze Ming Chong

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9 years ago.