How to understand the behavior of NVIC: i2c interrupt stay pending for a long time.

[nataliyadoni]

In my code I use i2c interface.  It works well for some time. But I found that in some revisions I had error in i2c interface.

I2c 100kHz, master.

After transmiting some bytes to slave i2c have stopped and in debug mode NVIC redisters show pending i2c interrupt.(NVICISPR0=0x01000000).

i2c_waitfor return 1.I

Below I show i2c interrupt code and waiting procedure.

I found this thing happends when the least byte of I2C0 interrupt code enter  and the least byte of  BNE.N  instruction in i2c_waitfor()  are the same. There is 512 byte between them.

Is  this my mistake or something wrong in processor pipeline?

What can you advise?

void I2C0_isr(void){

unsigned char Dum;

i2c_timeout=0;

I2C0_S |= I2C_S_IICIF_MASK;

   //ack

        if (i2c_adr_length>0){

          if (i2c_adr_length==2){I2C0_D = i2c_adr_ptr>>8;}else{I2C0_D = i2c_adr_ptr&0xff; } i2c_adr_length--; return;

           }else{

              if (i2c_curbyte==0){//конец адреса

               if ((I2C0_S&I2C_S_RXAK_MASK)!=0){i2c_Stop(); bus_error|=2;return;}

                     if (MasterTransmission == MRSW){i2c_EnterRxMode(); Dum = I2C0_D; i2c_curbyte=1;return;}  

                     if ((MasterTransmission&0x80) != 0){MasterTransmission&=0x7f;   IIC_ReStartTransmission(MasterTransmission);     return;

                    }

             }

  if (MasterTransmission == MWSR){// write

     if (i2c_curbyte==i2c_length){

        i2c_Stop();

    }else{

          if ((I2C0_S&I2C_S_RXAK_MASK)==0){

              I2C0_D = *i2c_buf_ptr++;

              i2c_curbyte++;

      }else{

       bus_error|=4;

        i2c_Stop();

      }

    }

  }else{

       // master read

    if (i2c_curbyte==i2c_length){

           i2c_Stop();

    }

     if (i2c_curbyte==(i2c_length-1)){

           i2c_DisableAck();

       } 

   *(uint8 *)(i2c_buf_ptr+i2c_curbyte-1) = I2C0_D;i2c_curbyte++;

  }

}

}

unsigned int i2c_waitfor(void){

while ((i2c_length > i2c_curbyte)||(((I2C0_S&0xf2)!=0x80))){

    if (i2c_timeout==60000){

    return(1);

   }

    i2c_timeout++;

  }

  return(0);

}

[yasuhikokoumoto]

Hello Nataliya,

although I cannot understand your program well but I think you seems not to clear NVIC interrupt.

NVIC always holds interrupt and in the corresponding ISR you should clear the interrupt by writing to NVICICPR0.

I hope this will help you.

Best regards,

Yasuhiko Koumoto.

[nataliyadoni]

Hello!

Thanks for your answer. But I thought that "when the processor enters the ISR, it automatically removes the pending state from the

interrupt"(Cortex_M4 Generic User Guide ), I see it in debug mode.

In ISR I clear IICIF.

And I repeat this thing happends when the least byteof the I2C0 ISR address  and the least byte of  BNE.N ??i2c_waitfor1 instruction address in i2c_waitfor()  are the same.

IICIF=1, BUSY=1. x( I2C priority is 0 (highest)).

When I add one NOP in i2c_waitfor this error disappears.

Please, look at a attached file.

I hope for your help,

Nataliya Doni.

[yasuhikokoumoto]

Hello Nataliya,

as long as the I2c interrupt remains, the NVIC will get the interrupt again until the interrupt source will be cleared (i.e.  IICIF is cleared).

Therefore, you should clear NVIC interrupt after clearing the IICIF.

Best regards,

Yasuhiko Koumoto.

[nataliyadoni]

Hello, Yasuhiko!

Thanks for reply.

I'll try it after weekend and I'll write about results.

Nataliya Doni.

[nataliyadoni]

Hello!

You are right.

I have made  a code with NVICICPR0=0x10000000 in I2c ISR and it helps me.

Thank you very much.

Best regards,

Nataliya Doni.

[yasuhikokoumoto]

Hello Nataliya,

good news! you are welcome.

Best regards,

Yasuhiko Koumoto.