Serial data mixed variables to array

Mes81

Hi.

I´m reading serial data. Package is 81 bytes long. I´m saving it to and array and it works as such.

Problem is that the stream consists data of 16-bit integers and 8-bit chars mixed. So the data gets mixed in the array.

Data stream:

byte 0 = (int) first 8-bits information 1 -> goes to array[0]

byte 1 = second 8-bits information 1 -> goes to array[0]

byte 2 = (char) 8-bits information 2 -> goes to array[1]

byte 3 = (int) first 8-bits information 3 -> half goes to array [1] and rest array[2]

byte 4 = second 8-bits information 3 -> half goes to array [2] and rest array[3]

byte 5 = (char) 8-bits information 4 -> goes to array [3]

---

So when I read array[1] it would have combined values of two information.

I can´t do nothing about the send protocol.

So what is the best way to get the information so it don´t get mixed?

kfrajer

Bit shifting!

Example

Array[0]=8 bits

Last 4 bits

Char chr0last = array[0] & 0x0f;

First 4 bits

Char chr0first = (array[0] &  0xf0)  >>4;

So now array[0]= (chr0first <<4) + chr0last;

This illustrates the concept of extracting group of bits. I used hex as it is customary. Last line I show how to merge group of bits to get new values (in this case I am restoring the. Orginal valuel)

I hope this helps,

Kf

Mes81

Thanks kfrajer. Bit shifting works! Did a simpler version to make sense of it.

int val = 46538; //46538=1011010111001010
int a; //first 8 bits=10110101=181 
int b; //last 8 bits=11001010=202

a = val >> 8; //= 000000010110101
println("Should get 181 ->"+a);


// & (bitwise AND)      
//Val=  1011010111001010
//0xff= 0000000011111111
//    = 0000000011001010
b = val & 0xff;                   
println("Should get 202 ->"+b);  

GoToLoop

// forum.Processing.org/two/discussion/16973/serial-data-mixed-variables-to-array
// GoToLoop (2016-Jun-03)

static final byte[] DATAGRAM = { 1, 2, 2, 1, 1, 1, 2 };
static final int SUM;

byte[] received = { 50, -120, 70, 43, -1, 95, -31, 100, -64, 1 };
final short[] converted = new short[DATAGRAM.length];

static {
  int sum = 0;
  for (final byte b : DATAGRAM) {
  assert b == 1 | b == 2 :
    b + " is invalid # of bytes!";

    sum += b;
  }
  SUM = sum;
}

void setup() {
  println(received.length, converted.length, SUM, ENTER);

assert SUM == received.length :
  SUM + " isn't " + received.length;

  byteToShortArr(received, converted, DATAGRAM);

  int idx = 0;
  for (final short sh : converted)  println(idx++, sh);

  exit();
}

static final short[] byteToShortArr(byte[] src, short[] tgt, byte... dgr) {
  if (src == null || dgr == null)  return tgt;
  if (tgt == null || tgt.length < dgr.length)  tgt = new short[dgr.length];

  int srcIdx = 0, tgtIdx = 0;

  for (final byte d : dgr) {
    final short s = src[srcIdx++];
    tgt[tgtIdx++] = (short) (d == 1? s & 0xFF : s<<010 | src[srcIdx++]);
  }

  return tgt;
}

Mes81

Thanks GoToLoop but your code is bit out of my talent range yet. But I will get back to it later.