Low Power LED Flasher on PFS154

LowPowerLEDflasher.c

/* ---------------------------------------------------
	Ultra Low Power LED flasher

	LED is connected to PA4 and is high active.

	Jan 16th, 2021,  CPLDCPU - Initial version

  ---------------------------------------------------- */
  
#include <stdint.h>
#include <pdk/device.h>
#include <pdk/delay.h>

unsigned char _sdcc_external_startup(void)
{
	PDK_SET_FUSE(FUSE_IO_DRV_LOW);	// Set output driving strength to low
	
	CLKMD =  CLKMD_ILRC | CLKMD_ENABLE_ILRC | CLKMD_ENABLE_IHRC; 
	CLKMD =  CLKMD_ILRC | CLKMD_ENABLE_ILRC ; 

		// Note: it is important to turn off IHRC only after clock settings
		// have been updated. Otherwise the CPU stalls.
	return 0; // perform normal initialization
}

void main(void)
{

	// Toggling PA4 at ILRC (53kHz): 86 µA
	// Toggling PA4 at ILRC_dev16 (53kHz): 66.7 µA
	// Stopsys with 5V: 0.5 µA
	// The watchdog cannot wake up from stopexe!!

	PADIER = 0; // disable pins as wakeup source
	PBDIER = 0; // Also port B needs to be disabled even if it is not connected
				// to the outside of the package. touching the package can introduce 
				// glitches and wake up the device

	INTEN = 0;  // Make sure all interrupts are disabled
	INTRQ = 0;

	MISC = MISC_FAST_WAKEUP_ENABLE;  // Enable faster wakeup (45 clocks instead of 3000)
									 // This is important to not waste energy, as 40µA bias is already added during wakeup time

	// Configure timer two for output on PA3
	// --> Works, timer2 and 2 can be used for PWM while CPU is in STOPEXE mode
	// It appears that also timer 2 can wake up the CPU. This is not maskable?

	TM2C  = TM2C_CLK_ILRC | TM2C_MODE_PWM;  // Oscilator source for timer 2 is LRC (53 kHZ)
	TM2CT = 0;
	TM2S  = TM2S_PRESCALE_DIV16 | TM2S_SCALE_DIV8; // Divide clock by 16*7=112 -> 53 kHz / 122 = 414 Hz    
	TM2B  = 1;  // PWM threshold set to 1. The PWM event will trigger the wakeup. Wakeup occurs with 414 Hz / 256 = 1.66 Hz

	PA		= 1<<4;  // LED is on PA4, set all other output to zero.
	PAPH 	= 0;	 // Disable all pull up resistors
	PAC		= 0;     // Disable all outputs
					 // Note: There is no series resistor for the LED
					 // The LED current is limited to 2-4 mA by LOW IO driving setting
					 // See Setction 4.14 (p24) in PFS154 manual

	for (;;) {	
		PAC |=1<<4;  // Enable LED output (It's set to High)
		__nop();
		__nop();
		__nop();
		PAC &=~(1<<4); // Disable LED output after 4 cycles => 4/53 kHz = 75.5 µS
		__stopexe();
	}
}