Electronic – way to write a generic GPIO code for MSP430

cgpiolibrarymsp430

I'm currently working on an MSP430 board and I'm trying to create libraries for it so I can easily use them on my project. I'm starting with basic Digital I/O functions.

Say for example I need to set P1.0 ON. In that case, normally what I do is:

P1SEL &= (~BIT0);           // Set P1.0 SEL for GPIO
P1DIR |= BIT0;              // Set P1.0 as Output
P1OUT |= BIT0;              // Set P1.0 HIGH

But I need to write a function that will just take Port Num, Pin and Value and set the above registers. Something like this:

void setVal(int x, int y) {
    PxSEL &= (~BITy);
    PxDIR |= BITy;
    PxOUT |= BITy;
}

Where x is Port and Y is Pin. Is there a way I can implement such a function? OR has this been done before? If yes, please share the link for the same. I was thinking out maybe using a lookup table and selecting the Register via indexing. But I'm not sure if that's a good approach. Any help would be appreciated.

Thanks

Best Answer

This can be done with a set of macros:

#define GPIO_MODE_GPIO(...)  GPIO_MODE_GPIO_SUB(__VA_ARGS__)
#define GPIO_MODE_GPIO_SUB(port, pin) (P##port##SEL &= ~(1<<pin)) // making an assumption about register layout here

#define GPIO_OUT_SET(...)  GPIO_OUT_SET_SUB(__VA_ARGS__)
#define GPIO_OUT_SET_SUB(port, pin) (P##port##OUT &= ~(1<<pin))

//etc...

The ## operator does string concatenation in the preprocessor. The two-level macros are used to allow a level of macro expansion to happen between the first and second macros, which allows you to do things like this:

#define LED_IO  1,5
GIPO_OUT_SET(LED_IO);

Without that extra indirection, the preprocessor would complain about not having enough arguments to the GPIO_OUT_SET macro.

This style of system has adapted quite well to every MCU I've used so far, from AVRs to ARMs, and since it's a preprocessor macro it compiles down into the smallest possible set of instructions.

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Electronic – Msp430 Launchpad Using Motor to Control Motor

My suggestion would be get rid of the delay function and use the built in if you are using IAR or CCS."__delay_cycles (cycles);" using the built ins, will give you more predicable results and better timing. You could probably just replace your delay for the built in, to get closer to the results you are looking for.

personally I would go about the whole thing using interrupts and timers to pull the whole thing off and use the peripherals that the msp430 has. I would suggest using the WDT as an interval timer, doing this would leave the other timer for your motor control. p1.3 is used as the wake up pin and p1.0 is the led pin.

example code

volatile int counter;
void main(void) {
    WDTCTL = WDTPW + WDTHOLD;                 // Stop watchdog timer
    P1DIR = 0x01;                             // P1.0 output, else input
    P1OUT =  BIT3;                            // P1.3 set, else reset
    P1REN |= BIT3;                            // P1.3 pullup
    P1IE |= BIT3;                             // P1.3 interrupt enabled
    P1IES |= BIT3;                            // P1.3 Hi/lo edge
    P1IFG &= ~BIT3;                           // P1.3 IFG cleared
    _BIS_SR(GIE);
}
// Port 1 interrupt service routine
#pragma vector=PORT1_VECTOR
__interrupt void Port_1(void)
{
    WDTCTL = WDT_MDLY_64; //enables intervals of 64mS
    IE1 |= WDTIE;  // set WDT interrupt
}
#pragma vector=WDT_VECTOR
__interrupt void watchdog_timer (void)
{
    ++counter;
    P1OUT |= BIT0;
    if (counter == 245) {  //245 x 64mS = 15.6 seconds
        P1OUT &= ~BIT0;
        WDTCTL = WDTPW + WDTHOLD; 
    }
}

Not complete nor has this code been tested, but it should turn the led on for 15 seconds every time the P1.3 button is pushed.

Electronic – MSP430 blinking led

You can download some code I wrote at:

ZIP file containing an LED Tutorial for MSP430

It covers everything from just turning an LED on, to causing it to evenly (to the eye) diminish and increase in intensity (which requires a geometric progression to achieve.)

In the meantime, what you didn't realize is the power-on value for P1OUT. Try two different statements BEFORE your for(;;) statement:

P1OUT &= ~0x01;

and

P1OUT |= 0x01;

And apply one or the other of the above with your latter code example (the one with the deleted code.) You will see two different behaviors. I'm not certain as I haven't researched it lately, but I suspect the P1OUT values are "random" upon power-on-reset. Regardless, it matters and you need to make sure that P1OUT values are "known" before starting your code.

In the case of your first code example that blinks the LED, the initial value didn't matter since the loop XORs the value over and over. You would never notice if it started as ON or OFF, because it is toggling all the time.

Best Answer

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