Variable rolling to 255

[psain.1]

I have STM32G070RBT6, a timer is set to give interrupt every 1 second, in interrupt i am incrementing a variable timer_var1 then in main file while loop i am dividing this by 10 and assigning this value to another variable TIMER_NOW.

Now when timer_var1 hits value 389(decimal) it rolls over to 255(dec).

there is nothing else in the while loop.

i am not able to figure out how is it possible.

code: 

volatile uint16_t timer_var1=0,TEMP,TIMER_PREV=0,TIMER_NOW=0;

  while (1)
  {

   TIMER_NOW=timer_var1/10;
//    if(TIMER_NOW>TIMER_PREV){
//    COR_Y[TIMER_NOW]=270-TEMP-TIMER_NOW*2;
//    COR_X[TIMER_NOW]=TIMER_NOW*7;
//        TIMER_PREV=TIMER_NOW;}

//   DWIN_DRAW_LINE(0x5000, COR_X,COR_Y, TIMER_NOW);

//   HAL_UARTEx_ReceiveToIdle_IT(&huart1, RX_BUFF_LCD, 16);

  HAL_Delay(300);

  HAL_GPIO_TogglePin(STATUS_GPIO_Port, STATUS_Pin);
    /* USER CODE END WHILE */

    /* USER CODE BEGIN 3 */
  }

In interrupt file:

/* USER CODE BEGIN PV */
extern volatile unsigned int DataPos;
extern volatile unsigned char RX_BUF[256u];
extern volatile uint16_t timer_var1;
/* USER CODE END PV */

void TIM1_BRK_UP_TRG_COM_IRQHandler(void)
{
  /* USER CODE BEGIN TIM1_BRK_UP_TRG_COM_IRQn 0 */
timer_var1++;
  /* USER CODE END TIM1_BRK_UP_TRG_COM_IRQn 0 */
  HAL_TIM_IRQHandler(&htim1);
  /* USER CODE BEGIN TIM1_BRK_UP_TRG_COM_IRQn 1 */

  /* USER CODE END TIM1_BRK_UP_TRG_COM_IRQn 1 */
}

[Sarra.S]

Hello @psain.1, 

In your code, timer_var1 is declared as volatile uint16_t, so it should hold values between 0 and 65535.

The fact that it's rolling back to 255, means that timer_var1 is being treated as an 8-bit variable somewhere in your code, maybe check all files where it is used, implicit conversions... 

[gbm]

My wild guess is stack overflow.

Which data items are declared at external level and which ones in the functions?

Show the declarations of all the data. Append a more complete code use "insert code sample" function of forum editor to make the code easily readable to anyone wishing to help you.

[Andrew Neil]

---

@gbm wrote:

use "insert code sample" function of forum editor to make the code easily readable to anyone wishing to help you.

---

@psain.1  - see the Posting Tips for full instructions on how to do that:

https://community.st.com/t5/community-guidelines/how-to-write-your-question-to-maximize-your-chances-to-find-a/ta-p/575228

[psain.1]

Both the files are attached, only here these variables are attached.. there was a lot of code there before this issue.

I removed it to find the cause of the problem and this is what is left.

[TDK]

Set a hardware watchpoint on the variable and it will break when it gets modified. Probably you have an out of bounds write somewhere, possibly to RAM_BUFF.

[psain.1]

I have narrowed down the issue this is after commenting line by line and testing i found that the these lines following function are cause of the problem.. still cannot figure out why

void DWIN_DRAW_LINE(int ADD, uint16_t cor_x[], uint16_t cor_y[], uint16_t size){
// TX_BUFF_LCD[0]=0x5A;TX_BUFF_LCD[1]=0xA5;TX_BUFF_LCD[3]=0x82;
// TX_BUFF_LCD[4]=(ADD&0xFF00)>>8;TX_BUFF_LCD[5]=ADD&0x00FF;
// TX_BUFF_LCD[6]=0x00;TX_BUFF_LCD[7]=0x02;
uint8_t lenght = 4*size;
// TX_BUFF_LCD[8]=00;TX_BUFF_LCD[9]=size-1;TX_BUFF_LCD[10]=0xF8;TX_BUFF_LCD[11]=0x00;
//
// for (int i = 0; i < (lenght); i += 4) {
// TX_BUFF_LCD[12 + i] = (cor_x[i/4] & 0xFF00) >> 8; // Higher byte
// TX_BUFF_LCD[13 + i] = cor_x[i/4] & 0x00FF; // Lower byte
// TX_BUFF_LCD[14 + i] = (cor_y[i/4] & 0xFF00) >> 8; // Higher byte
// TX_BUFF_LCD[15 + i] = cor_y[i/4] & 0x00FF; // Lower byte
// }
TX_BUFF_LCD[2]=lenght+11;
TX_BUFF_LCD[lenght+12]=0xFF;TX_BUFF_LCD[lenght+13]=0x00;
// HAL_UART_Transmit_IT(&huart1, TX_BUFF_LCD, (lenght+13));
}

the lines which are not commented are the problem

if i remove 

1. TX_BUFF_LCD[2]=lenght+11;  no change

2. TX_BUFF_LCD[lenght+12]=0xFF; timer_var1 rolls to 134

3. TX_BUFF_LCD[lenght+13]=0x00; timer_var1 rolls over to 511

if i change the type of TX_BUFF_LCD[] to uint16_t from uint8_t.. the the problem the issue goes away.. but that will make my entire code useless

Also i have removed unused code from originally uploaded main.c 

[psain.1]

I commented everything including RAM_BUFF usage

[Sarra.S · Accepted solution]

Hello @psain.1, 

Maybe implement a bounds checking mechanism to ensure that you do not write beyond the bounds of the TX_BUFF_LCD array 

 if (lenght + 12 < sizeof(TX_BUFF_LCD)) {
        TX_BUFF_LCD[lenght + 12] = 0xFF;
    }
    if (lenght + 13 < sizeof(TX_BUFF_LCD)) {
        TX_BUFF_LCD[lenght + 13] = 0x00;
    }

    // Ensure that the length does not exceed the buffer size
    if (lenght + 13 < sizeof(TX_BUFF_LCD)) {
        HAL_UART_Transmit_IT(&huart1, TX_BUFF_LCD, lenght + 13);
    }

 Also, you can add a break inside the loop to prevent writing beyond the buffer size if the calculated index exceeds the buffer size.

for (int i = 0; i < lenght; i += 4) {
        if (12 + i + 3 < sizeof(TX_BUFF_LCD)) {
            TX_BUFF_LCD[12 + i] = (cor_x[i / 4] & 0xFF00) >> 8; // Higher byte
            TX_BUFF_LCD[13 + i] = cor_x[i / 4] & 0x00FF;        // Lower byte
            TX_BUFF_LCD[14 + i] = (cor_y[i / 4] & 0xFF00) >> 8; // Higher byte
            TX_BUFF_LCD[15 + i] = cor_y[i / 4] & 0x00FF;        // Lower byte
        } else {
            // Prevent buffer overflow
            break;
        }

 step through the code and maybe we'll get stuck in one of the IFs

[gbm]

Value of timer_var1 above approx. 330 will result in overwriting some of the variables, presumably timer_var is overwritten. Ther is no check for range of 'size' var in DRAW_LINE, and TX_BUFF_LCD has a size of 150 only.

BTW. Do not use all-uppercase names for variables and routines.