/*

  Meter clock, version 2
  ----------------------

  Context: https://lcamtuf.substack.com/p/a-nicer-voltmeter-clock

  MCU: AVR128DA28

  Pinout: PC0, PC1, PC2 - PWM outputs to meters (other side to gnd)
          PA0, PA1      - 8 MHz crystal + 18 pF caps to gnd
          PD6, PD7      - time adjustment buttons (other side to gnd)

  The only other MCU connections are power supply pins and the UPDI
  programming header.

  Meter faces: https://lcamtuf.coredump.cx/soft/embedded/meter_clock2.pdf

  Complaints to: <lcamtuf@coredump.cx>

 */

#define F_CPU 8000000

#include <avr/io.h>
#include <util/delay.h>
#include <avr/interrupt.h>

/* User-friendly typedefs */

typedef int8_t   s8;
typedef uint8_t  u8;
typedef int16_t  s16;
typedef uint16_t u16;
typedef int32_t  s32;
typedef uint32_t u32;

/* Configure clock. External 8 MHz crystal on PA0, PA1 */

static void setup_clock() {

  CCP = 0xd8;                       /* Unlock register access   */
  CLKCTRL.XOSCHFCTRLA = 0b10000001; /* Enable external clock    */

  while(!(CLKCTRL.MCLKSTATUS & 0b10000));

  CCP = 0xd8;                       /* Unlock register access   */
  CLKCTRL.MCLKCTRLA = 3;            /* Switch to external clock */

  while(!(CLKCTRL.MCLKSTATUS & 1));

}

/* Configure ports. */

static void setup_ports() {

  PORTA.DIR = 0b11111111;
  PORTC.DIR = 0b11111111;
  PORTD.DIR = 0b00111111; /* PA6, PA7: buttons */
  PORTF.DIR = 0b11111111;

  /* Pull-up for buttons */
  PORTD.PIN6CTRL = 0b00001000;
  PORTD.PIN7CTRL = 0b00001000;

  /* Slew rate limit for PWM output */
  PORTC.PORTCTRL = 1;

}

/* Configure tick update interrupt to run at 10 Hz */

static void setup_timer() {

  TCA0.SINGLE.INTCTRL  = 0b00000001; /* OVF interrupt every PER cycles     */
  TCA0.SINGLE.CTRLA    = 0b00001100; /* Clock prescaler / 256 (31.250 kHz) */
  TCA0.SINGLE.PER      = 3125 - 1;   /* Effective frequency 10 Hz          */
  TCA0.SINGLE.CTRLA   |= 1;          /* Timer enable                       */

}

/* Update time, handling wrap-around. */

static volatile u8  cur_hr, cur_min;   /* Hour (0-11) and minute (0-59)     */
static volatile u16 cur_secx10;        /* Tenth of a second counter (0-599) */

ISR(TCA0_OVF_vect) {

  cur_secx10++;

  if (cur_secx10 == 600) {

    cur_secx10 = 0;
    cur_min++;

    if (cur_min == 60) {

      cur_min = 0;
      cur_hr++;

      if (cur_hr == 12)  cur_hr = 0;

    }

  }

  TCA0.SINGLE.INTFLAGS = 1; /* Acknowledge interrupt */

}

/* Main entry point */

int main(void) {

  setup_clock();
  setup_ports();
  setup_timer();
  sei();

  /* Main PWM loop. Synchronous counter running from 0 to 599 at several hundred kHz. */

  u16 duty_ctr = 0; /* PWM counter        */
  u8  key_last = 0; /* Previous key state */

  u16 adj_minx10, adj_hrx10, adj_secx10; /* Computed duty cycles for meters */

  while (1) {

    /* Compute duty cycles. The minute gauge has divisions from 0 to 60. One minute corresponds
       to a duty cycle step of 10, so we multiply the minute counter accordingly, and then add
       another value between 0 and 9 based on the state of the second counter.

       For the hour gauge, we have divisions from 0 to 12, and one hour corresponds to an
       increment of 50. We multiply the hour counter by 50 and add another 0-49 depending on
       the minute counter.

       This is also where you can incorporate fudge factors if the meters aren't precise. */

    if (!duty_ctr) {
      adj_minx10 = cur_min * 10 + cur_secx10 / 60,
      adj_hrx10  = cur_hr  * 50 + adj_minx10 / 12,
      adj_secx10 = cur_secx10;
    }

    /* PWM actuation */

    u8 pcval = 0;

    if (adj_secx10 > duty_ctr) pcval  = 0b100;
    if (adj_minx10 > duty_ctr) pcval |= 0b010;
    if (adj_hrx10  > duty_ctr) pcval |= 0b001;

    PORTC.OUT = pcval;
    duty_ctr++;

    /* After 600 cycles, we reset the PWM counter and check for keypresses. */

    if (duty_ctr == 600) {

      duty_ctr = 0;

      u8 pd = (PORTD.IN >> 6);

      /* Both inputs are high: reset state and continue */
      if (pd == 0b11) { key_last = 0; continue; }

      /* At least one button pressed. If this is a continuation of a previous keypress, bail out. */
      if (key_last) continue;
      key_last = 1;

      /* Key 1 advances the minute dial while zeroing the seconds. */
      if (!(pd & 0b10)) {
        cur_secx10 = 0;
        if (++cur_min == 60) cur_min = 0;
      }

      /* Key 0 advances the hour dial without messing up any of the other dials. */
      if (!(pd & 0b01)) {
        if (++cur_hr == 12) cur_hr = 0;
      }

    }

  }

}