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MSP430FR2355: bit field questions?

Steve Wenner
Genius 3240 points
Part Number: MSP430FR2355


Want to create a char (8 bits) where each bit represents a boolean flag T or F.  How do I do this?  Secondly will it only take up one char in memory?  Finally been reading and seems maybe I should use unsigned char?

  • 0
    Guru 42205 points

    Bitfields are very implementation defined, you really have to try it and see. Unsigned char are the way to go if you want to go this route. I think a better bet is to use a standard unsigned char and roll your own bit setting and testing operations, much like what TI has for the control registers.

  • 0 in reply to Keith Barkley
    Genius 3240 points

    Well here is my code and it seems to work.....Do you see any red flags:

    Within header file :

    struct userWakeFlags
{
    volatile unsigned char timerFlag : 1;
    volatile unsigned char adFlag : 1;
    volatile unsigned char keySwitchFlag : 1;
    volatile unsigned char timeMeasureFlag : 1;
};

    Initializing in main:

    struct userWakeFlags flags = {0};

    Use in main:

            if (flags.timerFlag) //compare
        {
            flags.timerFlag = F;

    The setting to F and T may be red flags?? but it seems to wrk

  • 0 in reply to Steve Wenner
    Guru 42205 points

    I don't know what F and T are, but that should work. The question is whether it is any more efficient than rolling your own.

  • 0 in reply to Keith Barkley
    Guru 100785 points

    Plus, you can't set more than one of them at a time. That's the fundamental weakness with defining machine registers that way [Ref Freescale]. And at their best they're nothing but syntactic sugar -- the CPU still has to do a RMW cycle. 

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