MSP430 clock problems after reset - real-time

Question

I use the following routine to configure the clock of my MSP430 (msp430g2231) microcontroller:
void configure_clock(void) {
if (CALBC1_1MHZ == 0xFF || CALDCO_1MHZ == 0xFF) { // Checks the clock constants
while(TRUE); // If callibration constants are erased, TRAP!
}
BCSCTL1 |= CALBC1_1MHZ; // Sets DCO range
DCOCTL |= CALDCO_1MHZ; // Set DCO step and modulation
BCSCTL1 &= ~(XTS | XT2OFF); // Disables XT2 and sets low frequency mode
BCSCTL3 |= (LFXT1S_0 | XCAP_3); // Selects LFXT1 crystal with 12,5pF
do {
IFG1 &= ~OFIFG;
__delay_cycles(1000);
} while (IFG1 & OFIFG); // Waits until crystal stabilizes
BCSCTL2 |= (SELM_2 | SELS); // Selects SMCLK and MCLK from LFXT1CLK
}
The problem is that the first time the code runs (just after powering up the microcontroller) everything works as expected and I get 32768 kHz clock. But if I press the reset button on the board (MSP430 Launchpad) the clock does not seem to work correctly, the code executes much slowly (like 10 times or so). Any ideas on the clock configuration?
Thanks!
Pere

Answer 1

First you can look at the power supply voltage. In case there is some spike during the startup then DCO wont work. In that case try to use a delay right before the Alignment of the values to BCSCTL1.
__delay_cycles(10000);
BCSCTL1 = CALBC1_1MHZ; // Sets DCO range
This will ensure that the startup spike is suppressed.
The next suspect would be decoupling on your target board. I mean the Capacitor on the VCC as well as the one used in the Reset. TI recommends 1nF-2nF for the Reset line and a 0.1uF for the VCC. But in case you are using the LaunchPad as you platform then that should not be a problem.
Also for the calibration value assignments use assignment operators and not logical operators. As the other values being 0 is a default.
BCSCTL1 = CALBC1_1MHZ; // Set DCO
DCOCTL = CALDCO_1MHZ;
If you are planning to Run the XT2 it is not available in G2231. Its LFXT1 directly.
You dont need explicit initialization for the 32.768KHz crystal to work.
It just work when you power up. So the additional initialization step is not needed.
In order to find better help please have a look at slac463a for software examples related to clock setting.

Answer 2

The only things I can suggest with your code are below. Whether or not they fix your issue I don't know as it seems strange that the first run is OK but after a reset it is not. Do you access the clock configuration anywhere else? What code do you call on reset?
You always use bit manipulation to include or exclude values into the registers. You should start with a known value and then adjust bits from there otherwise you may be incorporating bits from a previous state. For example, instead of:
BCSCTL1 |= CALBC1_1MHZ;
BCSCTL1 &= ~(XTS | XT2OFF);
You can set it to a definitive value by doing something like this:
BCSCTL1 = XT2OFF | (CALBC1_1MHZ & 0x0F);
The other suggestion is that XT2OFF has to be set in order to turn off XT2. You are clearing the bit, so are leaving it on. This is in conflict with your comment so might be an error.