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

	LED is connected to PA4 and is high active.

	Jan 16th, 2021,  CPLDCPU - Initial version
	Jan 17th, 2021,  Adaptive voltage

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

void PulseLED(uint8_t);
uint8_t MeasureSupply(void);

unsigned char _sdcc_external_startup(void)
{
//	PDK_SET_FUSE(FUSE_IO_DRV_LOW);	// Set output driving strength to low
	// PDK_SET_FUSE(FUSE_IO_DRV_NORMAL);	// 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;
}

const uint8_t PWTAB[]={1,2,2,2,3,3,4,6,9,9,9,9,9,9,9,9};
uint8_t LEDcycles=0;
uint8_t updatecounter=10;

void main(void)
{
	// 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 | MISC_LVR_DISABLE;  // Enable faster wakeup (45 clocks instead of 3000)
									 					// This is important to not waste energy, as 40µA bias is already added during wakeup time
														// Disable LVR (optional)

	// 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*8=128 -> 53 kHz / 128 = 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 Section 4.14 (p24) in PFS154 manual
					 // The output is disabled when the LED is off to avoid leakage

	for (;;) {	
		PulseLED(LEDcycles);

		if (!--updatecounter) {
			uint8_t adc=MeasureSupply();
			LEDcycles=PWTAB[adc];
			updatecounter=10;
		}
		__stopexe();  // Put MCU in power down mode until wakeup by timer
	}
}

void PulseLED(uint8_t cycles) {
	PA  |=1<<4;

	switch(cycles) {		
		case 1: PAC |=1<<4;PAC &=~(1<<4);break;
		case 2: PAC |=1<<4;__nop();PAC &=~(1<<4);break;
		case 3: PAC |=1<<4;__nop();__nop();PAC &=~(1<<4);break;
		case 4: PAC |=1<<4;__nop();__nop();__nop();PAC &=~(1<<4);break;
		case 5: PAC |=1<<4;__nop();__nop();__nop();__nop();PAC &=~(1<<4);break;
		case 6: PAC |=1<<4;__nop();__nop();__nop();__nop();__nop();PAC &=~(1<<4);break;
		case 7: PAC |=1<<4;__nop();__nop();__nop();__nop();__nop();__nop();PAC &=~(1<<4);break;
		case 8: PAC |=1<<4;__nop();__nop();__nop();__nop();__nop();__nop();__nop();PAC &=~(1<<4);break;
		default:
		case 9: PAC |=1<<4;__nop();__nop();__nop();__nop();__nop();__nop();__nop();__nop();PAC &=~(1<<4);break;	
	}	
}

/*
	Uses the internal comparator to measure the supply voltage

*/

uint8_t MeasureSupply(void) {

	GPCC = GPCC_COMP_ENABLE | GPCC_COMP_MINUS_BANDGAP_1V2; // Activate comparator. Negative input is Bandgap, Positive input is resistor ladder
	// We use case 3 withg GPCS.4 =0 and .5 = 1, So Vinternal=0.25*Vdd+(n+1)/32
	// gpcc.6 is 1 when Vresistor > VBG

	// SAR ADC using the internal resistor ladder
	__asm
		mov		a, #0x20  ; GPCS.4 = 0  GPCS.5 = 1

		or      a, #0x08   ; Bit 3
		mov     __gpcs,a
		t0sn    __gpcc, #6
		xor     a, #0x08

		or      a, #0x04   ; Bit 2
		mov     __gpcs,a
		t0sn    __gpcc, #6
		xor     a, #0x04

		or      a, #0x02   ; Bit 1
		mov     __gpcs,a
		t0sn    __gpcc, #6
		xor     a, #0x02

		or      a, #0x01   ; Bit 0
		mov     __gpcs,a
		t0sn    __gpcc, #6
		xor     a, #0x01

		and     a,#15	// Result is now in A register.

		set0    __gpcc,#7  ; turn comparator off
	__endasm;

// debug output
// outputs a long pulse for 1, a short pulse for zero
#if 0
	__asm
		mov		p, a	
		set1    __pac,#3

		sl 		a
		set1    __pa,#3
		swapc	__pa,#3
		set0    __pa,#3

		sl 		a
		set1    __pa,#3
		swapc	__pa,#3
		set0    __pa,#3

		sl 		a
		set1    __pa,#3
		swapc	__pa,#3
		set0    __pa,#3

		sl 		a
		set1    __pa,#3
		swapc	__pa,#3
		set0    __pa,#3

		sl 		a
		set1    __pa,#3
		swapc	__pa,#3
		set0    __pa,#3

		sl 		a
		set1    __pa,#3
		swapc	__pa,#3
		set0    __pa,#3

		sl 		a
		set1    __pa,#3
		swapc	__pa,#3
		set0    __pa,#3

		sl 		a
		set1    __pa,#3
		swapc	__pa,#3
		set0    __pa,#3

		mov		a, p
	__endasm;
#endif
	__asm 
		ret
	__endasm;

	return 0; // to get rid of warning. This line is never executed
}