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I2C_transfer - repeated start?

JimG
Intellectual 560 points
Other Parts Discussed in Thread: CC3200

If an I2C_transfer specifies a write followed by a read, will there be two completely separate I2C bus transactions or will a repeated start be used?  

  • 0
    TI__Mastermind 20480 points

    It should be a repeated start, though it shouldn't matter to your I2C peripheral. From an RTOS task perspective it is atomic.

  • 0 in reply to Tom Kopriva
    Intellectual 560 points

    Thanks for your help.

    I think that most peripherals are going to be tolerant of a stop then start in place of a repeated start, but I believe that in some instances the governing spec really does indicate repeated start.  For example, isn't that what PMBus uses for things like ReadByte?

    In our situation (single master bus), it really isn't too important, but if you have a PMBus peripheral on a multi-master bus, it can be necessary in order to assure that another master doesn't interfere with your command.

    It would be nice to know for sure that I2C_transfer will use a repeated start.

  • 0 in reply to JimG
    TI__Mastermind 20480 points

    Jim,

    I believe the TI-RTOS documentation states that the I2C driver does not support a multi-master bus. I've submitted an enhancement request (SDOCM00113569) to add this support.

    I haven't used PMBus specs yet, so I don't know to what extent the I2C driver is compatible with the PMBus specs.

    What device are working with? On TivaC, CC3200, and MSP430 [E]USCI devices, I am certain that for those devices the I2C driver issues an actual repeated start bit.

  • 0 in reply to Tom Kopriva
    Intellectual 560 points

    I'm using a Tiva device - TM4C1231DSPZ.  It sounds like I'll get a repeated start, then.  That sounds great.

    Thank you!