Serial buffer extension for SAMD21 feather m0 express board

Shivamiitk · November 9, 2022, 10:14am

Hello i am using an atmel based SAMD21 microcontroller Feather M0 express board.
I want to increase the serial buffer size to receive 100 bytes of data from uart of a different microcontroller.

I am trying to follow the following link, will this be the right approach ?

https://www.hobbytronics.co.uk/arduino-serial-buffer-size#:~:text=However%2C%20this%20data%20buffer%20is,vast%20amount%20of%20RAM%20available.

I have a doubt that in this tutorial the core mentioned is of AVR, but i am using a samd21 which is arm based. Please let me know what should be my approach?

Thanks,
Shivam

sterretje · November 9, 2022, 10:51am

Study Robin's Serial Input Basics - updated to get ideas how to solve your problem (without hacking the core). Change const byte numChars = 32 to the desired size.

westfw · November 9, 2022, 8:01pm

I believe the serial buffer size on samd21 boards is already 256 bytes. ArduinoCore-samd/Uart.h at master · arduino/ArduinoCore-samd · GitHub

Shivamiitk · November 10, 2022, 5:38am

@ sterretje Yes, this is a correct way of solving the issue. But i don't want to change my existing program logic as implementing this will require to change the existing logic of the code.

Thanks,
Shivam

westfw · November 10, 2022, 5:44am

Actually, it turns out that Adafruit has increased the buffer size to 350 bytes on their SAMD21 boards...

github.com

adafruit/ArduinoCore-samd/blob/master/cores/arduino/RingBuffer.h#L31


      
          #ifndef _RING_BUFFER_
          #define _RING_BUFFER_
          
          #include <stdint.h>
          
          // Define constants and variables for buffering incoming serial data.  We're
          // using a ring buffer (I think), in which head is the index of the location
          // to which to write the next incoming character and tail is the index of the
          // location from which to read.
          
          #ifndef SERIAL_BUFFER_SIZE
          #define SERIAL_BUFFER_SIZE 350
          #endif
          
          template <int N>
          class RingBufferN
          {
            public:
              uint8_t _aucBuffer[N] ;
              volatile int _iHead ;
              volatile int _iTail ;

Shivamiitk · November 10, 2022, 7:07am

westfw Thanks, i will check. Actually the task is that i am reading a 100 byte string terminated by \n from a SD card via SPI protocol using arduino function readStringUntil('\n') and after reading the string i am doing some data processing on it. So when i am reading upto 56 bytes. The results are as expected but when i am increasing the number of bytes to be read then the results are not correct.
What should i do ?

sterretje · November 10, 2022, 7:33am

Show your code.

Where does the serial buffer fit in this? SPI does not use the buffer that you want to increase.

I have no reason not to believe @westfw, so whatever it is, your logic is flawed.

Shivamiitk · November 10, 2022, 8:16am

@ sterretje Okay, so now this is the problem i have to solve. Actually i was earlier using uart instead of spi. But now i am using SPI.
Here is my code:

 if (Filec) {
    Serial.println("test.txt:");

    // read from the file until there's nothing else in it:
    int i=0;
    int j=0;
    while (Filec.available()) 
    {

      String Dc = Filec.readStringUntil('\n');
      int ind1 = Dc.indexOf(',');
      delay (20);
      int ind2 = Dc.indexOf(',',ind1+1);
      delay (20);
      int ind3 = Dc.indexOf(',',ind2+1);
      delay (20);
      int ind4 = Dc.indexOf(',',ind3+1);
      delay (20);
          A = Dc.substring(0,ind1);
          delay (20);
          B = Dc.substring(ind1+1,ind2);
          delay (20);
          C = Dc.substring(ind2+1,ind3);
          delay (20);
          D = Dc.substring(ind3+1);
          delay (20);
          Serial.print(A);
          Serial.print("  ");
          delay (25);
          Serial.print(B);
          Serial.print("  ");
          delay (25);
          Serial.print(C);
          Serial.print("  ");
          delay (25);
          Serial.print(D);
          Serial.println();
          delay (25);
          if (i<32)
          {
          arr [i][j]   = A.toFloat();
          arr [i][j+1] = B.toFloat();
          arr [i][j+2] = C.toFloat();
          arr [i][j+3] = D.toFloat();
          i=i+1;
          }
          else 
          {
            i=0;
          }
          
          Serial.println("                         ");
          Serial.println("Now printing float values");
          Serial.println("                         ");
          Serial.print(arr[i][j]);
          Serial.print("   ");
          delay(25);
          Serial.print(arr[i][j+1]);
          Serial.print("   ");
          delay(25);
          Serial.print(arr[i][j+2]);
          Serial.print("   ");
          delay(25);
          Serial.println(arr[i][j+3]);
          delay(25);
      } 
    Filec.close();
    }    

    // close the file:

     
    else 
    {
    // if the file didn't open, print an error:
    Serial.println("error opening test.txt");
    }

I have attached the snapshot for the result, i am getting 4 "0.00" which should not be such values.

sterretje · November 10, 2022, 10:20am

Please post full code or at least code that we can compile and test.

Please post a small example if the data on the card or that you want to read (couple of lines). Or attach a small example file.

Shivamiitk · November 10, 2022, 12:29pm

Here is the code below:

#include <SPI.h>
#include <SD.h>
#include <Arduino.h>   // required before wiring_private.h
#include "wiring_private.h" // pinPeripheral() function
#include <U8x8lib.h>
#include <Wire.h>
#include <Adafruit_NeoPixel.h>
#ifdef __AVR__
#include <avr/power.h> // Required for 16 MHz Adafruit Trinket
#endif
#define PIN      8
#define NUMPIXELS 1
#define SERIAL_BUFFER_SIZE 256 
Uart Serial2 (&sercom1, 11, 10, SERCOM_RX_PAD_0, UART_TX_PAD_2);
void SERCOM1_Handler()
{
  Serial2.IrqHandler();
}
File dataFile;
File Filec;
String Data;
String A;
String B;
String C;
String D;
String R;
String Ch;
float arr [32][3]; //3 column
int k=0;
int l=0;
char timestamp[30];
const int chipSelect = 6;
void setup() 
{
  Serial1.begin(9600);
  Serial2.begin(9600);
  Wire.begin();
  // Assign pins 10 & 11 SERCOM functionality
  pinPeripheral(10, PIO_SERCOM);
  pinPeripheral(11, PIO_SERCOM);
  Serial2.print("Initializing SD card...");
  if (!SD.begin(chipSelect)) 
  {
    Serial2.println("Card failed, or not present");
    return;
  }
  Serial2.println("card initialized.");
  delay(2000);
  Filec = SD.open("test.txt");
  if (Filec) {
    // read from the file until there's nothing else in it:
    int i=0;
    int j=0;
    while (Filec.available()) 
    {

      String Dc = Filec.readStringUntil('\n');
      int ind1 = Dc.indexOf(',');
      delay (20);
      int ind2 = Dc.indexOf(',',ind1+1);
      delay (20);
      int ind3 = Dc.indexOf(',',ind2+1);
      delay (20);
      int ind4 = Dc.indexOf(',',ind3+1);
      delay (20);
          A = Dc.substring(0,ind1);
          delay (20);
          B = Dc.substring(ind1+1,ind2);
          delay (20);
          C = Dc.substring(ind2+1,ind3);
          delay (20);
          D = Dc.substring(ind3+1);
          delay (20);
          Serial.print(A);
          Serial.print("  ");
          delay (25);
          Serial.print(B);
          Serial.print("  ");
          delay (25);
          Serial.print(C);
          Serial.print("  ");
          delay (25);
          Serial.print(D);
          Serial.println();
          delay (25);
          if (i<32)
          {
          arr [i][j]   = A.toFloat();
          arr [i][j+1] = B.toFloat();
          arr [i][j+2] = C.toFloat();
          arr [i][j+3] = D.toFloat();
          i=i+1;
          }
          else 
          {
            i=0;
          }
          
          Serial.println("                         ");
          Serial.println("Now printing float values");
          Serial.println("                         ");
          Serial.print(arr[i][j]);
          Serial.print("   ");
          delay(25);
          Serial.print(arr[i][j+1]);
          Serial.print("   ");
          delay(25);
          Serial.print(arr[i][j+2]);
          Serial.print("   ");
          delay(25);
          Serial.println(arr[i][j+3]);
          delay(25);
      } 
    Filec.close();
    }    

    // close the file:  
    else 
    {
    // if the file didn't open, print an error:
    Serial.println("error opening test.txt");
    }
}

void loop() 
{

}

This is the attached file which i am reading from the SD card.
WD002.txt (2.3 KB)

david_2018 · November 10, 2022, 12:53pm

print defaults to two decimal places for floats, if you want to print more decimal places you need to specify how many:

Serial.print(arr[i][j], 7); //print seven decimal places

Also you need to check how float is implemented on the Feather M0, there is a limit to how many significant digits can be stored, might need to use double.

gfvalvo · November 10, 2022, 12:54pm

You're better off biting the bullet now and doing it correctly rather than trying to patch up a hacky solution.

Shivamiitk · November 10, 2022, 1:20pm

@ david_2018 yes, i am now using the following code below but i am not getting the exact decimal places matching. I am attaching a snapshot of image showing comparison of what i am able to read as float and how the numbers are stored in txt file.

#include <SPI.h>
#include <SD.h>
#include <Arduino.h>   // required before wiring_private.h
#include "wiring_private.h" // pinPeripheral() function
#include <U8x8lib.h>
#include <Wire.h>
#include <Adafruit_NeoPixel.h>
#ifdef __AVR__
#include <avr/power.h> // Required for 16 MHz Adafruit Trinket
#endif
#define PIN      8
#define NUMPIXELS 1
#define SERIAL_BUFFER_SIZE 256 
Uart Serial2 (&sercom1, 11, 10, SERCOM_RX_PAD_0, UART_TX_PAD_2);
void SERCOM1_Handler()
{
  Serial2.IrqHandler();
}
File Filec;
String Data;
String A;
String B;
String C;
String D;
float arr [32][4]; //3 column
const int chipSelect = 6;
void setup() 
{
  Serial1.begin(9600);
  Serial2.begin(9600);
  Wire.begin();
  // Assign pins 10 & 11 SERCOM functionality
  pinPeripheral(10, PIO_SERCOM);
  pinPeripheral(11, PIO_SERCOM);
  Serial2.print("Initializing SD card...");
  if (!SD.begin(chipSelect)) 
  {
    Serial2.println("Card failed, or not present");
    return;
  }
  Serial2.println("card initialized.");
  delay(2000);
  Filec = SD.open("test.txt");
  if (Filec) {
    // read from the file until there's nothing else in it:
    int i=0;
    int j=0;
    delay(1000);
    Serial.println("     Printing coefficients          ");
    delay(1000);
    while (Filec.available()) 
    {

      String Dc = Filec.readStringUntil('\n');
      int ind1 = Dc.indexOf(',');
      delay (20);
      int ind2 = Dc.indexOf(',',ind1+1);
      delay (20);
      int ind3 = Dc.indexOf(',',ind2+1);
      delay (20);
      int ind4 = Dc.indexOf(',',ind3+1);
      delay (20);
          A = Dc.substring(0,ind1);
          delay (20);
          B = Dc.substring(ind1+1,ind2);
          delay (20);
          C = Dc.substring(ind2+1,ind3);
          delay (20);
          D = Dc.substring(ind3+1);
          delay (20);
          if (i<32)
          {
          arr [i][j]   = A.toFloat();
          arr [i][j+1] = B.toFloat();
          arr [i][j+2] = C.toFloat();
          arr [i][j+3] = D.toFloat();
          Serial.print(arr[i][j],16);
          Serial.print("   ");
          delay(25);
          Serial.print(arr[i][j+1],16);
          Serial.print("   ");
          delay(25);
          Serial.print(arr[i][j+2],16);
          Serial.print("   ");
          delay(25);
          Serial.println(arr[i][j+3],16);
          delay(25);
          i=i+1;
          }
          else 
          {
            i=0;
          }
      } 
    Filec.close();
    }    

    // close the file:  
    else 
    {
    // if the file didn't open, print an error:
    Serial.println("error opening test.txt");
    }
}

void loop() 
{

}

txt file containg the data to be read and stored as float.

WD002.txt (2.3 KB)

david_2018 · November 10, 2022, 3:11pm

Try using double instead of float.

Shivamiitk · November 11, 2022, 9:10am

@ david_2018 It worked using double thanks. Now my doubt is when i am using double and storing this number into a variable will it use all 15 decimal digits for calculation or less digits it will use? Since for serial.print i am doing serial.print(arr[i][j],16) but for calculation there is no such command but i want to use all decimal digits in the formula so that the results are accurate.
Thanks,
Shivam

sterretje · November 11, 2022, 9:54am

Calculations are done with the type (double in your case). The 16 in the serial prints is only for text representation.

Shivamiitk · November 11, 2022, 9:56am

So you mean all decimal digits will be used in calculations.

sterretje · November 11, 2022, 10:16am

Yes

system · May 10, 2023, 10:16am

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Serial buffer extension for SAMD21 feather m0 express board

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