The LaunchPad and many other demo/experimental boards all have a push-button switch connected to the nRST/NMI pin. Can this switch be used as input during execution of Application firmware?
I made an attempt to do so and demonstrate it by turning on/off an LED controlled by P1.0 (another common feature of LaunchPand other demo/experimental boards). I would like to hear from you guys if I made any mistake or had any blind spot in this example code.
Please note that because nRST/NMI pin is also the SBWTDIO pin. Thus you should not press this push-button while you are using SBW.
/*******************************************************************************
* Demo Program for LaunchPad Board *
* Using S1 at nRST/NMI Pin as Input for Application *
* OCY Oct 2010 *
*******************************************************************************/
#include <msp430.h>
#define FLIP_HOLD (0x3300 | WDTHOLD) /* flip HOLD while preserving other bits */
//
#define S1_MAKE P1OUT |= BIT0 /* turn on LED1 for demo */
#define S1_BREAK P1OUT &= ~BIT0 /* turn off LED1 for demo */
//
void main (void)
{
// We use the red LED1 at P1.0 to demostrate that we can detect
// the switch s1 at nRST/NMI pin as an input
P1OUT &= ~BIT0;
P1DIR |= BIT0;
// The WDT will be used exclusively to debounce s1
WDTCTL = WDTPW | WDTHOLD | WDTNMIES | WDTNMI;
IFG1 &= ~(WDTIFG | NMIIFG);
IE1 |= WDTIE | NMIIE;
// The CPU is free to do other tasks, or go to sleep
__bis_SR_register(CPUOFF | GIE);
}
//==============================================================================
// isr to detect make/break of s1 at the nRST/NMI pin
#pragma vector = NMI_VECTOR
__interrupt void nmi_isr(void)
{
if (IFG1 & NMIIFG) // nmi caused by nRST/NMI pin
{
IFG1 &= ~NMIIFG;
if (WDTCTL & WDTNMIES) // falling edge detected
{
S1_MAKE; // tell the rest of the world that s1 is depressed
WDTCTL = WDT_MDLY_32 | WDTNMI; // debounce and detect rising edge
}
else // rising edge detected
{
S1_BREAK; // tell the rest of the world that s1 is released
WDTCTL = WDT_MDLY_32 | WDTNMIES | WDTNMI; // debounce and detect falling edge
}
} // Note that NMIIE is cleared; wdt_isr will set NMIIE 32msec later
else {/* add code here to handle other kinds of nmi, if any */}
}
//==============================================================================
// WDT is used exclusively to debounce s1 and re-enable NMIIE
#pragma vector = WDT_VECTOR
__interrupt void wdt_isr(void)
{
WDTCTL ^= FLIP_HOLD; // Flip the HOLD bit only, others remain unchanged
IFG1 &= NMIIFG; // It may have been set by switch bouncing, clear it
IE1 |= NMIIE; // Now we can enable nmi to detect the next edge
}
//==============================================================================
