Program execution time and latency

Projects Programming
1

Hi,

I am using Arduino to receive, process commands and derive another machine. I am using Arduino UNO

See the code below:

#include <SPI.h> 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <SoftwareSerial.h>    // This feature is for second serial port
SoftwareSerial mySerial(2,3); // RX, TX

/*------- SPI Pin assignments ----------
SCK             13
SDO             11
SDI             12
CNV             05 (SS)
FREFH Out       09
RESETn          06
Soft Serial Rx  02
Soft Serial Tx  03
---------------------------------------*/
char *ptr = NULL;
uint16_t receivedData; //  We will read data in this for displaying later
uint16_t sendData; // Unsigned Integer of 16 bit width
uint16_t sendData1;// Included for testing
const byte CLOCKOUT = 9;   
#define slaveSelect 5
#define resetOutput 6 
 
SPISettings settingsA(1000000, MSBFIRST, SPI_MODE2); // Mode 2 means, SCK will remain 1 in inactive, and will sample on negative edge, will work on 8 MHz

/*---------------------------This is the function that will generate the SPI transaction------------------------*/
void SPITransactionSettingsA(uint16_t a) {
  PORTD = PORTD | (B00100000);  // Writting to pin 5 // digitalWrite (slaveSelect, HIGH);
  SPI.beginTransaction(settingsA);
  receivedData = SPI.transfer16(a);
  SPI.endTransaction();
  PORTD = PORTD & ~(B00100000); // Writting to pin 5 // Previously digitalWrite(slaveSelect, LOW);
  //Serial.print("The received data from SPI is:"); // Will print values in Hexadecimal
  //Serial.print(receivedData, HEX); // Will print values in Hexadecimal
  //Serial.print("\n"); // Will print values in Hexadecimal
}


void setup() {
   Serial.begin(115200);
   mySerial.begin(115200); // Previously 154000
   SPI.begin();
   pinMode(slaveSelect,OUTPUT);
   pinMode (CLOCKOUT, OUTPUT);
   TCCR1A = bit (COM1A0);  
   TCCR1B = bit (WGM12) | bit (CS10);   
   OCR1A =  0;      
   pinMode(resetOutput,OUTPUT);
   PORTD = PORTD &~(B1111111); 
   PORTD = PORTD |  (B01000000); // Putting Reset to 1 initially
}

void loop() {
    if(Serial.available()){
        String data = Serial.readString(); 
        unsigned long StartTime = millis();
        if ((data.substring(0,5)) == "RESET"){
           PORTD = PORTD & ~(B01000000);  
           PORTD = PORTD |  (B01000000);
           }
        else {
        String IntermediateData = data.substring(0,4);
        sendData = strtoul(IntermediateData.c_str(),&ptr,16);
        SPITransactionSettingsA(sendData);
    }
        unsigned long CurrentTime = millis();
        unsigned long ElapsedTime = CurrentTime - StartTime;
        mySerial.println(ElapsedTime);//(sendData1); // This line I included just to see whether or where it prints
    }
    
}

Problems: When I send command with an interval of 1010ms, everything works fine. But as I decrease time, even to 1009ms, only first command gets executed.

I tried to measure the timing of execution of program, but it reports that the loop executed in 0 time. So here are two problems:

  1. What time it is taking to execute the function SPITransactionSettingsA.
  2. Why 1010ms, why cant it process faster?

Thanks in advance.

@johnwasser

2

I'd certainly expect the SPI stuff to run a few microseconds, not sure what the 1010 v 1009ms issue is.

The reset pulse you drive is suspiciously short, less than a microsecond, what is it supposed to be talking to?

If you post the circuit too, that will answer a heap of questions in one go...

3

Could your problem be the readString?

4

Line endings perhaps?
How are you determining “only the first command gets executed”?

When something is received, something should execute. Either the RESET or the SPI transaction. That is a given from the structure of your code.
If neither of those is happening (which is what you are stating) then the conclusion should be that nothing is being received....