Error while sending stop condition for I2c

Posted on June 26, 2013 at 14:51

I might have got something wrong, but:

    while( stop_sent == 0 );

doesn't make sense to me.

You are comparing a variable with a constant in a loop. On match, this loop is endless, otherwise a NOP.

Posted on June 26, 2013 at 15:39

                if( tx_idx == 7 )                     /* send stop condition */

 

                {

 

                    I2C3->CR1 |= I2C_CR1_STOP;        /* generate a stop condition */

 

                    tx_idx++;

 

                    stop_sent = 1;

 

                }    

 

With the above code tx_idx will be 8 at least.

Try something like this:

                if( tx_idx == 7 )                     /* send stop condition */

 

                {

 

                    if(!stop_sent)

 

                    {

 

                      I2C3->CR1 |= I2C_CR1_STOP;        /* generate a stop condition */

 

                      stop_sent = 1;

 

                    }

 

                }    

 

 

Posted on June 26, 2013 at 16:00

Is stop_sent declared as volatile?  Otherwise results are unpredictable.

  Jack Peacock

Posted on July 12, 2013 at 14:14

1. I had again cheked the code and noticed that even after sending stop conditoin code goes to following interrupt else part:

            case I2C_EVENT_MASTER_BYTE_TRANSMITTING:  /* EV8 , TRA, BUSY, MSL, TXE flags  */

            case I2C_EVENT_MASTER_BYTE_TRANSMITTED:   /* EV8_2, TRA, BUSY, MSL, TXE and BTF flags  */

                if( tx_idx == 7 )                     /* send stop condition */

                {

                    I2C3->CR1 |= I2C_CR1_STOP;        /* generate a stop condition */

                    tx_idx++;

                    stop_sent = 1;

                }    

                else

                {

                    I2C3->DR = tx_buffer[tx_idx++] ;               /* Transmit the data  */     

                }    

2. Yes all vars are volatile.

3. Coming back to ISR again indicates that there some ISR flag pending but I had cleared all by reading the registers, but don't what causes that. When code comes to stop condition in ISR then value of event var is = 0x00070080.

4. Can anyone check at my code & see if my initialization stpes & ISR are correct

Posted on July 13, 2013 at 14:28

STM32 doc says:

EV8_2: TxE=1, BTF = 1, Program Stop request. TxE and BTF are cleared by hardware by the Stop condition

I think you should set

I2C_CR1_STOP

 only when you get 

2C_EVENT_MASTER_BYTE_TRANSMITTED 

(BTF=1). 

To me it looks like you handle one request which should be ignored.