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[C6727] I2C Issue

hiro10784
Intellectual 260 points

Hello, folks.

I'm encountered this phenomena with I2C accessing without CSL. (with CSL, it seem to be fine)

In CSL, It natularry waiting while running some redundant code, I think.

Accesssing I2Cx_CNT and  I2Cx_MDR is need some wait between them.

This is may not documented. (I  couldnot find it ; )

Best regards

 

  • TI__Guru*** 125430 points

    What processor are you using?  Also, there are a lot of good tips on I2C here.  Can you please share a code snippet where you need to put a delay between these accesses?  What you've described so far does not bring any problems to mind.

    Brad

  • in reply to Brad Griffis
    Intellectual 260 points

    Hi, Brad. I'm using C6727 @ 300MHz

    here is code fragment works well. not wait, not works well.

    void init_i2c( void )
    {
     I2C1_MDR = 0; // IRS=0  make reset state
     I2C1_PSC = 17;
     I2C1_CLKL = 34;
     I2C1_CLKH = 34;

     I2C1_IER = 0;

     I2C1_EMDR = 1;
     
     I2C1_MDR = ( (1<<10) | (1<<9) ); // MST,TRX=1  master, transmit
     I2C1_OAR = 5;  // owner address

     I2C1_PFUNC = 0;   // GPMODE=0   not GPIO
     I2C1_MDR |= (1<<5);  // IRS=1

     while( (I2C1_MDR & (1<<5) )== 0 ){ // until IRS=1 (I2C is enabled) [timeout needed?]
      asm(" nop");
      asm(" nop");
      asm(" nop");
      asm(" nop");
     }

     I2C1_SAR = 0x1a; // AIC23 adrs

    }

    void send_i2c( u8 reg, u8 dat )
    {

     I2C1_CNT = 2;  // 2byte send

     while( (I2C1_STR & (1<<12) ) ){  // wait while bus busy  [timeout needed???]
      asm(" nop");  // for BP  while debug
      asm(" nop");
      asm(" nop");
      asm(" nop");
     }

     t_wait();  // this wait is needed for right working

     I2C1_MDR |= (1<<10);  // MST make master
     I2C1_MDR |= (1<<13);  // STT make start condition
    // I2C1_MDR = 0x2e20;

     while( (I2C1_STR & (1<<4) )==0 ){  // wait until ICXRDY==1 [timeout needed???]
      asm(" nop");  // for BP while debug
      asm(" nop");
      asm(" nop");
      asm(" nop");
     }
     I2C1_DXR = reg & 0xff;
     while( (I2C1_STR & (1<<4) )==0 ){  // wait until ICXRDY==1 [timeout needed???]
      asm(" nop");
      asm(" nop");
      asm(" nop");
      asm(" nop");
     }
     I2C1_DXR = dat & 0xff;
     while( (I2C1_STR & (1<<4) )==0 ){  // wait until ICXRDY==1 [timeout needed???]
      asm(" nop");
      asm(" nop");
      asm(" nop");
      asm(" nop");
     }

     I2C1_MDR |= (1<<11);  // STP make stop condition


    }

  • in reply to hiro10784
    TI__Guru*** 125430 points

    Hiro,

    No, the delays are not necessary.  I believe the pertinent info in your case is under the "back to back transfers" heading in the I2C tips wiki page I referenced previously.  Specifically, at the end of a transfer you should poll for MST==0 before beginning another one.

    I recommend making the following changes to your code to implement this efficiently:

    1. In your init function, do NOT set the MST bit.  Allow this to be completed in the "send" function.
    2. At the start of your send function, poll for MST==0.
    3. You should now be able to remove the unnecessary waits...

    Also, I highly recommend that you add a check for NACKs in your code as mentioned in the wiki page.  If for some reason you ever received a NACK (board issue) then your software would permanently stick in the loop polling for XRDY.  If however you check for NACK it could actually printout a diagnostic, retry, etc.

    Brad