Reading data at 10 Khz rate

Yes you are absolutely right though its reads corrects value some times but once its looses its sync it does take lot of value to again com its actual position. So what could i do to make to once it looses its sync on next or in 2-3 iteration its sync again. :frowning: :frowning:

const int pin2 = 2;
const int pin4 = 4;
int clock = 0;
int clock1 = 0;



void setup()
{
  pinMode(pin2, INPUT);
   
  pinMode(pin4, INPUT);
  
  Serial.begin(2400);
}
void loop()
{
     static byte num_bits  = 0;
     static byte value = 0;

     clock = digitalRead(pin2);
     if ((clock == HIGH) && (clock1 == LOW))
        {   

            
            value = (value << 1) | digitalRead (pin4);
            if (++num_bits >= 8)                          // have we done 8 iterations?  If so print it out
                {
                     Serial.print(value, HEX);
                     Serial.println();
                     num_bits = 0;
                    value = 0;
                }
        }

    clock1= clock;
}

Just for curiosity can ISR(edge triggered) be used at that frequency

newbee_2:
Yes you are absolutely right though its reads corrects value some times but once its looses its sync it does take lot of value to again com its actual position. So what could i do to make to once it looses its sync on next or in 2-3 iteration its sync again. :frowning: :frowning:

Reading through Rob's code, if it loses its way, it will/should pick up the next preamble characters so long as the 4-bit boundary is maintained. So if you've got out of sync by 1, 2 or 3 bits one way to potentially make it pick up the trail sooner is to construct a state machine looking for the pattern of bits of the preamble rather than the sequence of nibbles (which wouldn't be found if you are no longer sampling nibbles at the correct bit boundary). Also, presuming there's a bit on every high clock pulse I'm wondering if the marked line below, will mean the first ever bit in the stream is always lost which would throw it out of sync from the start?

byte getNibble() {

    byte val = 0;
    
    for (byte bit_count = 0; bit_count < 4; bit_count++) {
        while (digitalRead(CLOCK_PIN) == HIGH);  // <<< THIS LINE
        while (digitalRead(CLOCK_PIN) == LOW);
        val <<= 1;
        val |= digitalRead(DATA_PIN); 
    }
    return (val &= 0x0F);
}

You do say it works, so I presume I'm wrong on that point.

Geoff

It might get a bit tight Geoff, after getting a nibble you have ~100uS to get back to the getNibble() function. If you don't make it you are out of sync again. I'll have a think about the timing but it may be better to put that code inline, at least that will save a function call.

You do say it works, so I presume I'm wrong on that point.

I'm not sure newbee_2 is using my code.

One thing I/we didn't think of is that presumably the PC still needs to see the preamble as it doesn't know all this is happening. So after we get in sync we need to send those 6 bytes.


Rob

can ISR(edge triggered) be used at that frequency

Yes, and that may be a good way to go. But if we're worried about having enough time interrupts will make it worse.


Rob

Ok this code is most efficient so far once it goes out of Sync in 2-3 iteration it comes back but they are saying make it like sliding window and you keep on sliding 1 bit at a time until you found the match("CAAC1F") and when found send it reaming bits(128-24=104) and again start the process. Can it be done?
Thanks and Regards
Niladri

this code is most efficient so far

Which code are we talking about now?

2-3 iteration

What is an "iteration" in this context?

Can it be done?

I think that's what my example did but I haven't revisited it because I don't know if you have tried it or not.


Rob

The code on post 32.
Some time that code also looses its Sync but once it looses it comes back after 2-3 wrong value
No in that code you have checked only 32 byte and after you skip a pules but data stream is continuous so pulse skip might not possible

const int CLOCK_PIN     =     2;
const int DATA_PIN      =     4;
const int PACKET_BITS   =     128;
const int PREAMBLE_LEN  =    6;
const int DATA_LEN      =    ((PACKET_BITS / 4) - PREAMBLE_LEN);

enum {
    PRE_0,    PRE_1,    PRE_2,    PRE_3,    PRE_4,    PRE_5,    DATA
} states;    

byte     preamble [] = {0x0C,0x0A,0x0A,0x0C,0x01,0x0F};
char     hexAsciiVals[] = "0123456789ABCDEF";
byte     state = PRE_0;
byte     nibble;
int        nibble_count = 0;

void setup() {
  pinMode(CLOCK_PIN, INPUT);
  pinMode(DATA_PIN, INPUT);
  Serial.begin(9600);
}

void loop() {

    nibble = getNibble();
    nibble_count++;
    
    switch (state) {    
        case PRE_0:
            if (nibble_count > 32) { // I made this change for my own understanding
                // we've read 32 bytes and still not found a match 
                // for the preamble so skip a clock pulse
                while (digitalRead(CLOCK_PIN) == HIGH);
                while (digitalRead(CLOCK_PIN) == LOW);
                nibble_count = 0;
            } else {
                state = (nibble == preamble[0]) ? PRE_0 : PRE_1;
            }
            break;
        
        case PRE_1:
            state = (nibble == preamble[1]) ? PRE_0 : PRE_2;    
            break;
            
        case PRE_2:
            state = (nibble == preamble[2]) ? PRE_0 : PRE_3;
            break;

        case PRE_3:
            state = (nibble == preamble[3]) ? PRE_0 : PRE_4;
            break;

        case PRE_4:
            state = (nibble == preamble[4]) ? PRE_0 : PRE_5;
            break;
        
        case PRE_5:
            state = (nibble == preamble[5]) ? PRE_0 : DATA;
            break;
            
        case DATA:
            Serial.write (hexAsciiVals[nibble]);
            if (nibble_count == DATA_LEN) {
                // all done, start again
                state = PRE_0;
                nibble_count = 0;
            }
            break;
    }
}

byte getNibble() {

    byte val = 0;
    
    for (byte bit_count = 0; bit_count < 4; bit_count++) {
        while (digitalRead(CLOCK_PIN) == HIGH);
        
          while (digitalRead(CLOCK_PIN) == LOW);
        
          val <<= 1;
          val |= digitalRead(DATA_PIN);
        
          
    }
    return (val &= 0x0F);
}

So if it goes out of sync it recovers with the loss of no more than 3 frames of data. Is that acceptable to you or do you need to refine that further?

Hi guys I am back with another problem.
If i want to read the data exactly on each rising edge using interrupt how to approach that way???
All other things mentioned earlier still remains same ( reading "CAAC1F" and match found read the next remaining 32 bytes of data).
I have never written an ISR and pretty clueless how to set the proper register(currently i am going through the datasheet but without any background knowledge i am struggling a lot)
Any help???
Thanks in advance
Niladri

Hi Niladri

Can you share the code as you have it presently?

Geoff

Sorry this is the present code

const int CLOCK_PIN     =    2;
const int DATA_PIN      =    4;
const int PACKET_BITS   =    128;
const int PREAMBLE_LEN  =    6;
const int DATA_LEN      =    26;

enum {
    PRE_0,    PRE_1,    PRE_2,    PRE_3,    PRE_4,    PRE_5,    DATA
} states;    

byte     preamble [] = {0x0C,0x0A,0x0A,0x0C,0x01,0x0F};
char     hexAsciiVals[] = "0123456789ABCDEF";
byte     state = PRE_0;
byte     nibble;
int        nibble_count = 0;

void setup() {
  pinMode(CLOCK_PIN, INPUT);
  pinMode(DATA_PIN, INPUT);
  Serial.begin(115200);
}

void loop() {

    nibble = getNibble();
    nibble_count++;
    
//    Serial.print(digitalRead(CLOCK_PIN));
    
    switch (state) {    
        case PRE_0:
            if (nibble_count > 32) {
                // we've read 32 bytes and still not found a match 
                // for the preamble so skip a clock pulse
                while (digitalRead(CLOCK_PIN) == LOW);
                while (digitalRead(CLOCK_PIN) == HIGH);
                nibble_count = 0;
            } 
            else 
            {
                if(nibble == preamble[0]) 
                      state = PRE_1;
                else
                      state = PRE_0;
            }
            break;
            
        case PRE_1:
            if(nibble == preamble[1]) 
                 state = PRE_2;
            else
                 state = PRE_0;    
            break;
            
        case PRE_2:
            if(nibble == preamble[2]) 
                state = PRE_3;
            else
                state = PRE_0;
            break;
            
        case PRE_3:
            if(nibble == preamble[3]) 
               state = PRE_4;
            else
               state = PRE_0;
            break;
            
        case PRE_4:
            if(nibble == preamble[4]) 
              state = PRE_5;
            else
              state = PRE_0;
            break;
            
        case PRE_5:
            if(nibble == preamble[5])
             state = DATA;
            else
             state = PRE_0;
            break;
            
        case DATA:
            Serial.print (hexAsciiVals[nibble]);
            if (nibble_count == DATA_LEN) {
                // all done, start again
                state = PRE_0;
                nibble_count = 0;
                Serial.println();
            }
            break;
    }
}

byte getNibble() {

    byte val = 0;
    
    for (byte bit_count = 0; bit_count < 4; bit_count++) {
        while (digitalRead(CLOCK_PIN) == HIGH);
        
          while (digitalRead(CLOCK_PIN) == LOW);
          val <<= 1;
          val |= digitalRead(DATA_PIN);
        }
    return (val &= 0x0F);
}

Finally it's working thanks everyone for their help and support without your help it would not been possible and i am posting the working code if in case anyone wants to refer it for their future use....
Thanks...

const int CLOCK_PIN     =     2;
const int DATA_PIN      =     4;
const int PACKET_BITS   =     256;
const int PREAMBLE_LEN  =     6;
const int DATA_LEN      =     ((PACKET_BITS / 4) - PREAMBLE_LEN);

enum {
    PRE_0,    PRE_1,    PRE_2,    PRE_3,    PRE_4,    PRE_5,    DATA
} states;    

byte     preamble [] = {0x0C,0x0A,0x0A,0x0C,0x01,0x0F};
char     hexAsciiVals[] = "0123456789ABCDEF";
byte     state = PRE_0;
byte     nibble;
int      nibble_count = 0;
byte     firstval;

void setup() {
  pinMode(CLOCK_PIN, INPUT);
  pinMode(DATA_PIN, INPUT);
  Serial.begin(9600);
}

void loop() {

    nibble = getNibble();
    //nibble_count++;
    
    
    switch (state) {    
        case PRE_0:
//            if (nibble_count > PREAMBLE_LEN + DATA_LEN) {
//                // we've read 32 bytes and still not found a match 
//                // for the preamble so skip a clock pulse
//                while (digitalRead(CLOCK_PIN) == LOW);
//                while (digitalRead(CLOCK_PIN) == HIGH);
//                nibble_count = 0;
//            } else 
//            {
//                firstval = 12;
//                Serial.write(hexAsciiVals[firstval]);
                
                state = (nibble == preamble[0]) ? PRE_1 : PRE_0;
              //  Serial.write(hexAsciiVals[nibble]);
//            }
            break;
        
        case PRE_1:
            
           // Serial.write (hexAsciiVals[firstval]);
           // Serial.print(hexAsciiVals[12]);
            Serial.print(hexAsciiVals[nibble]);
            state = (nibble == preamble[1]) ? PRE_2 : PRE_0;    
            //Serial.write (hexAsciiVals[nibble]);
            break;
            
        case PRE_2:
            Serial.print(hexAsciiVals[nibble]);
            state = (nibble == preamble[2]) ? PRE_3 : PRE_0;
            //Serial.write (hexAsciiVals[nibble]);
            break;

        case PRE_3:
            Serial.print(hexAsciiVals[nibble]);
            state = (nibble == preamble[3]) ? PRE_4 : PRE_0;
            //Serial.write (hexAsciiVals[nibble]);
            break;

        case PRE_4:
            Serial.print(hexAsciiVals[nibble]);
            state = (nibble == preamble[4]) ? PRE_5 : PRE_0;
            //Serial.write (hexAsciiVals[nibble]);
            break;
        
        case PRE_5:
            Serial.print(hexAsciiVals[nibble]);
            state = (nibble == preamble[5]) ? DATA : PRE_0;
            //Serial.write (hexAsciiVals[nibble]);
            //   nibble_count = 0;
            break;
            
        case DATA:
           
            Serial.print(hexAsciiVals[nibble]);
            if (nibble_count == DATA_LEN) {
                // all done, start again
                state = PRE_0;
                nibble_count = 0;
                Serial.println(' ');
                Serial.print(hexAsciiVals[12]);
                
            }
            
            nibble_count++;
            //Serial.println();
            break;
    }
    
  //  delay(10);
}

byte getNibble() {

    byte val = 0;
    
    for (byte bit_count = 0; bit_count < 4; bit_count++) {
        while (digitalRead(CLOCK_PIN) == HIGH);
        while (digitalRead(CLOCK_PIN) == LOW);
        val <<= 1;
        val |= digitalRead(DATA_PIN); 
    }
    return (val &= 0x0F);
}

Just for curiosity i tried to read byte by byte rather than nibble by nibble but it does not read the data at all. Can anybody indicate where i am doing wrong.

const int CLOCK_PIN     =     2;
const int DATA_PIN      =     4;
const int PACKET_BITS   =     1024;
const int PREAMBLE_LEN  =     3;
const int DATA_LEN      =     ((PACKET_BITS / 8) - PREAMBLE_LEN);

enum {
    PRE_0,    PRE_1,    PRE_2,    PRE_3,    PRE_4,    PRE_5,    DATA
} states;    

byte     preamble [] = {0xCA,0xAC,0x1F};
char     hexAsciiVals[] = "0123456789ABCDEF0123456789ABCDEF";
byte     state = PRE_0;
byte     nibble;
int      nibble_count = 0;
byte     firstval;
//const char  header = "CAAC1F";

void setup() {
  pinMode(CLOCK_PIN, INPUT);
  pinMode(DATA_PIN, INPUT);
  Serial.begin(57600);
}

void loop() {

    nibble = getNibble();
    //nibble_count++;
    
    
    switch (state) {    
        case PRE_0:
//            if (nibble_count > PREAMBLE_LEN + DATA_LEN) {
//                // we've read 32 bytes and still not found a match 
//                // for the preamble so skip a clock pulse
//                while (digitalRead(CLOCK_PIN) == LOW);
//                while (digitalRead(CLOCK_PIN) == HIGH);
//                nibble_count = 0;
//            } else 
//            {
//                firstval = 12;
//                Serial.write(hexAsciiVals[firstval]);
                
                state = (nibble == preamble[0]) ? PRE_1 : PRE_0;
              //  Serial.write(hexAsciiVals[nibble]);
//            }
            break;
        
        case PRE_1:
            
           // Serial.write (hexAsciiVals[firstval]);
           // Serial.print(hexAsciiVals[12]);
           // Serial.print(hexAsciiVals[nibble]);
            state = (nibble == preamble[1]) ? PRE_2 : PRE_0;    
            //Serial.write (hexAsciiVals[nibble]);
            break;
            
        case PRE_2:
          //  Serial.print(hexAsciiVals[nibble]);
            state = (nibble == preamble[2]) ? DATA : PRE_0;
            //Serial.write (hexAsciiVals[nibble]);
            break;

//        case PRE_3:
//          //  Serial.print(hexAsciiVals[nibble]);
//            state = (nibble == preamble[3]) ? PRE_4 : PRE_0;
//        //    Serial.write (hexAsciiVals[nibble]);
//            break;
//
//        case PRE_4:
//           // Serial.print(hexAsciiVals[nibble]);
//            state = (nibble == preamble[4]) ? PRE_5 : PRE_0;
//           // Serial.write (hexAsciiVals[nibble]);
//            break;
//        
//        case PRE_5:
//           // Serial.print(hexAsciiVals[nibble]);
//    //        Serial.print(202, HEX);
//  //          Serial.print(172, HEX);
//        //    Serial.println();
//            state = (nibble == preamble[5]) ? DATA : PRE_0;
//            Serial.print("$");
//            //   nibble_count = 0;
//            break;
            
        case DATA:
           //   Serial.print("CAAC1F");
            Serial.print(nibble, HEX);
            if (nibble_count == DATA_LEN) {
                // all done, start again
                state = PRE_0;
                nibble_count = 0;
             //   Serial.print("\n");
           //     Serial.print(hexAsciiVals[12]);
                
            }
            
            nibble_count++;
            //Serial.println();
            break;
    }
    
  //  delay(10);
}

byte getNibble() {

    byte val = 0;
    
    for (byte bit_count = 0; bit_count < 8; bit_count++) {
        while (digitalRead(CLOCK_PIN) == HIGH);
        while (digitalRead(CLOCK_PIN) == LOW);
        val <<= 1;
        val |= digitalRead(DATA_PIN); 
    }
    return (val &= 0xFF);
}

Hi,

This thread takes me back :slight_smile:

Rob's state machine was based on testing the 4 bit nibbles, so you'd have to rewrite that too, not just the getNibble() function. I'd be concerned though that while the previous logic could be out of sync with the stream by up to 3 bits, this could get lost by up to 7. This would lead to potentially more than double the data loss on those occasions while the sketch found the correct preamble again.

Why would you want to do it byte by byte? Didn't you have this working as at your previous post?

Geoff

No it is working fine and there no necessity for me make it 8 bit but for just better understanding that if the state machine works for 4 bit then if we do slight modification on the state machine it should work for 8 bit. So i modified the state machine as well as getNibble() function but it does not read any data so i came to forum for possible solution(I am work alone so i have no other alternative). :slight_smile:

Okay,

So for the sake of the exercise then :slight_smile:

Can I ask why have you commented out the block at the start of case PRE_0: ? Without it surely if you start out of sync there's no way it can recover, so it could read the entire stream without ever discovering a valid preamble therefore will never find you any data.

Geoff

That's true but i need to shift bit by bit until i find a match so skipping a clock might not be best method as the data might be the particular preamble first bit(the preamble can be anywhere i don't where it starts so shift bit by bit 1st until match found).

Skipping a clock is just ignoring the next one bit so the next frame is read from 1 bit to the right in alignment down the stream. It's only done when there's been a full frame length read without finding a preamble (which means it's out of sync and always would be).

Where is your code for returning to alignment if you're not doing that?