Access to timer TCNT3 on YUN board

Using Arduino Programming Questions
1

Hello,

I try to read timer TCNT3 value (16bits) using direct acces to timer registers (TCNT3L & TCNT3H with 8bits access (First read to TCNT3L 0x0094 and after to TCNT3H 0x0095) on YUN board (timer inside ATMEGA32U4).

But even if this timer is 16bits wide I read always 0x00 for TCNT3H ???

My sketch does only this task, I have disabled interrupt during reading to both registers but I never see high Bytes changung!!!

Others associated topic:
I believe that TCNT3L and TCNT3H addresses are define inside files *.h but when I want use them, sketch compiles but the value change at each compilation ???
So Ibelieve the "Constant" are not define but I don't get an error at compilation! If I use other register address undefined (i.e UBRR1H) in this case I get an error!

Thanks for your help.

2

Your sketch seems to got lost during posting.
You can directly access TCNT3, the compiler will do the correct code to read the registers.

3

hi, Here this is my sketch:

// put your setup code here, to run once:

volatile uint8_t *ptrTIMER = 0x0094;// Value used to address Timer TCNT3 

void setup() {
  Serial.begin(9600);
  while (!Serial) {
    ; // wait for serial port to connect. Needed for native USB port only
  }

  Serial.print("ptrTIMER point to address 0x");
  Serial.println((uint32_t) ptrTIMER, HEX);

  uint8_t *pointeurOctet1 = (uint8_t*) ptrTIMER; // pointeurOctet adress one Byte, read access byte per byte

  // First value read 
  Serial.print("Byte0 (TCNT3L) address 0x");
  Serial.print((uint8_t) pointeurOctet1, HEX);
  Serial.print(" est 0x");
  Serial.println(*pointeurOctet1, HEX);
  
  // Second Byte read
  Serial.print("Byte1 (TCNT3H) address 0x");
  Serial.print((uint8_t) (pointeurOctet1 + 1), HEX);
  Serial.print(" est 0x");
  Serial.println(*(pointeurOctet1 + 1), HEX);
  
  Serial.println();

  int i;
  uint8_t ValTimerH;
  uint8_t ValTimerL;
  
  for (i=0;i<4;i++) {

  noInterrupts();
  ValTimerL = *pointeurOctet1;
  ValTimerH = *(pointeurOctet1+1);
  interrupts();
  
  Serial.print("Byte0 at address 0x");
  Serial.print((uint8_t) pointeurOctet1, HEX);
  Serial.print(" est 0x");
  Serial.print(ValTimerL, HEX); 
  Serial.print(" Byte1 at address 0x");
  Serial.print((uint8_t) pointeurOctet1+1, HEX);
  Serial.print(" est 0x");
  Serial.print(ValTimerH, HEX); 
  Serial.println(" ");
    
  }

  Serial.println(" ");

  volatile uint8_t *ptrTCNT3L = TCNT3L;
  volatile uint8_t *ptrTCNT3H = TCNT3H;

  Serial.println("Values of the pre-declared timer register address : ");
  Serial.print("TCNT3L @0x");
  Serial.print((uint32_t) TCNT3L, HEX);
  Serial.print(" TCNT3H @0x");
  Serial.println((uint32_t) TCNT3H, HEX);
  Serial.print("TCNT3L @0x");
  Serial.print((uint32_t) TCNT3L, HEX);
  Serial.print(" TCNT3H @0x");
  Serial.println((uint32_t) TCNT3H, HEX);

  Serial.println();

  Serial.print("Value pointed by ptrTCNT3L  @0x");
  Serial.print((uint16_t) ptrTCNT3L, HEX);
  Serial.print(" 0x");
  Serial.println((uint8_t) *ptrTCNT3L, HEX); 
  
  Serial.print("Value pointed by ptrTCNT3H  @0x");
  Serial.print((uint16_t) ptrTCNT3H, HEX);
  Serial.print(" 0x");
  Serial.println((uint8_t) *ptrTCNT3H, HEX);

  Serial.println();

}

void loop() {
  // put your main code here, to run repeatedly:

}
4

Don't do such stuff. The development environment comes with all defines you need, let the compiler do the low level stuff, it won't make the mistakes you did.

It's that easy:

uint16_t counter_value = TCNT3;

5

Hi Pylon,

Thanks for your help, all is fine now!

I have learned something today, great day! :slight_smile:

Regards

6

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