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(Context: I'm an experienced embedded systems engineer, just dipping my toe into MSP430-land. My target system is an MSP-EXP430FR5994 LaunchPad dev board.) General goal: How do I wake the processor N ticks in the future, where one tick is 1/32768 second and N can be as large as 2^15? My first thought was to use the RTC, but that appears to have a resolution of 1 second. My second thought was to use a timer module (e.g. TA1) and use its compare interrupt to wake the processor from LPM4. So my questions: Is there a better / alternative way to wake the processor N ticks in the future? Table 6-1 ("Operating Modes") states that a "COMP" event can wake the processor from LPM4. Does "COMP" refer to a compare interrupt from a timer? Is there a block diagram of the counter module(s) somewhere? I didn't see it in the processor-specific datasheet.
Did anybody been succesful in writing to the SD card on the FR5994? For me the out of the box demo does not work for SD-logging. When re-installing it, no idea whether it worked when originally came out of the box ;-( Is there a "hello world on SD card" example using the fr5994 around somewhere? update: yesterday it did not work and I did not know why today I got it working (the out of the box project) and I do not know why.... ;-)
The example msp430fr5994x_lpm4-5_02.c is supposed to show how little current is used in this mode. In the file it says: // MSP430FR5x9x Demo - Entering and waking up from LPM4.5 via P1.3 interrupt // with SVS disabled // // Description: Download and run the program. When entered LPM4.5, no LEDs // should be on. Use a multimeter to measure current on JP1 and // compare to the datasheet. When a positive voltage is applied // to P1.3 the device should wake up from LPM4.5. This will enable // the LFXT oscillator and blink the LED (on P1.0). Even for a high-end multimeter this current is too low to be accurately measured. So I helped myself this way: - power the processor from the supercap - a 10k resistor with two antiparallel diodes act as a shunt, - connect the volt meter across the supercap, not across the processor 0.43mV over a 10k resistor gives 43 Nanoamps. (!) Yes, the datasheet (page 32) is right, typical value at 25°C is 45nA. A CR2032 (200mAh) cell would allow the processor to wait for an interrupt for 530 years.