// by Ido Gendel, 2020
// Share and enjoy!

#include <SI_EFM8BB1_Register_Enums.h>

char msg[] = "Hello World!        \n"; // Includes room for numbers
const uint8_t lastDigitPos = 19;
volatile char *cp;

// Do not read directly - use millis()
volatile uint32_t _millis = 0;

const uint8_t DEBOUNCE_MS = 10;
volatile uint8_t debounceMSLeft;
uint8_t oldButtonState = 1;


// This function is called immediately after reset, in SILABS_STARTUP.A51
void SiLabs_Startup (void) {

    // Disable watchdog
	WDTCN = 0xDE;
	WDTCN = 0xAD;

}


uint32_t millis(void) {

	uint32_t result;

	IE_EA = 0; // Disable interrupts
	result = _millis;
	IE_EA = 1; // Re-enable interrupts
	return result;

}


void setup(void) {

	P1MDOUT |= P1MDOUT_B4__PUSH_PULL; // Set built-in LED pin (P1.4) to push-pull output
	// Built-in button pin (P0.2) digital input by default
	// Weak pull-ups enabled by default.
	P0_B2 = 1;// Turn WPU on for button input

	// Default clock is internal 24.5MHz div 8
	// As a default, timers 0/1 uses system clock div 12 prescaler
	TMOD |= TMOD_T1M__MODE2; // Set Timer1 mode to 8-bit auto-reload
	TH1 = 243; // Set reload value to produce OVF @19.2KHz
	TCON_TR1 = 1; // Enable timer1

	TMOD |= TMOD_T0M__MODE1; // Set Timer0 mode to 16-bit
    TH0 = 0xFF; // Set Timer0 counter to overflow after 255 "ticks"
    TL0 = 0x01;
	TCON_TR0 = 1; // Enable timer0

	// Enable UART in crossbar; TX pin (P0.4) will become output automatically
	XBR0 |= XBR0_URT0E__ENABLED;
	// Enable crossbar
	XBR2 = 0x40;

	IE_ET0 = 1; // Enable timer0 interrupt
	IE_ES0 = 1; // Enable UART0 interrupt
	IE_EA = 1; // Enable interrupts globally

}


void populateSecondsText(void) {

	uint8_t i = lastDigitPos;
	uint32_t s = millis() / 1000;

	do {
		msg[i--] = s % 10 + 48;
		s = s / 10;
	} while (s > 0);

}


int main (void) {

	setup();

	for ( ; ; ) {

		if ((0 == debounceMSLeft) && (P0_B2 != oldButtonState)) {

			debounceMSLeft = DEBOUNCE_MS;
			oldButtonState = P0_B2;
			if (P0_B2) {

				P1_B4 = 0; // LED ON
				populateSecondsText();
				cp = &msg[1];
				SBUF0 = msg[0]; // Start UART transmission

			}

		}

	}

}


SI_INTERRUPT (TIMER0_OVF_ISR, TIMER0_IRQn) {

	// Interrupt flag is cleared automatically
    TH0 = 0xFF; // Reload counter value
    TL0 = 0x01;
    ++_millis;
    if (debounceMSLeft) {
    	--debounceMSLeft;
    }

}

SI_INTERRUPT (UART0_ISR, UART0_IRQn) {

	// Transmit interrupt flag must be cleared in firmware:
	SCON0_TI = 0;

	// Anything left to transmit? (assuming null-terminated string)
	if (0 != *cp) {
		SBUF0 = *cp++;
	} else {
		P1_B4 = 1; // LED OFF
	  }

}