/* Serial LED Display - see http://www.technoblogy.com/show?3US2

   David Johnson-Davies - www.technoblogy.com - 23rd March 2022
   ATtiny85 @ 8 MHz (internal oscillator; BOD disabled)
   
   CC BY 4.0
   Licensed under a Creative Commons Attribution 4.0 International license: 
   http://creativecommons.org/licenses/by/4.0/
*/

#include <SPI.h>

// Globals
const int cs = 3;                               // Display CS pin; use 1 for ATtiny402
const int Brightness = 8;                       // Can be between 0 and 15
const int DP = 0x80;                            // Segment pattern for decimal point
const int Space = 16;
const int Minus = 17;
const int Equals = 18;

const uint8_t Segs[19] = {
0x7e, 0x30, 0x6d, 0x79, 0x33, 0x5b, 0x5f, 0x70, 0x7f, 0x7b, // 0 to 9
0x77, 0x1f, 0x4e, 0x3d, 0x4f, 0x47,                         // A to F
0x00, 0x01, 0x09                                            // space, minus, equals
};

class SerialDisplay : public Print {
  public:
    void init();
    size_t write(uint8_t);
    void clear();
    void show(uint8_t, uint8_t);
  private:
    void cmd(uint8_t, uint8_t);
    uint8_t cur = 0;
    uint8_t last = 0;
};

// Send a two-byte display command
void SerialDisplay::cmd (uint8_t a, uint8_t d) {
  digitalWrite(cs, LOW);
  SPI.transfer(a);
  SPI.transfer(d);
  digitalWrite(cs, HIGH);
}

// Show a segment pattern on a particular display
void SerialDisplay::show (uint8_t d, uint8_t pat) {
 cmd(8-d, pat);
}

// Clear display
void SerialDisplay::clear () {
 for (int d=0; d<8; d++) show(d, Space);
 cur = 0;
}

// Initialise the display
void SerialDisplay::init () {
 cmd(0xF, 0);                                   // Test mode off
 cmd(0xB, 7);                                   // 8 digits
 cmd(0x9, 0x00);                                // Decode segments
 cmd(0xA, Brightness);
 clear();
 cmd(0xC, 1);                                   // Enable display
}

// Write to the current cursor position 0 to 7 and handle scrolling
size_t SerialDisplay::write (uint8_t c) {
  if (c == '\n') {
    cur = 0;                                    // Return resets cursor
    return 1;
  } else if (c == ' ') {
    last = Segs[Space];
  } else if (c == '.') {
    last = last | DP;                           // Decimal point on previous display
    if (cur != 0) cur--;
  } else if (c == '-') {
    last = Segs[Minus];
  } else if (c == '=') {
    last = Segs[Equals];
  } else if (c >= '0' && c <= '9') {            // Digit
    last = Segs[c-'0'];
  } else if ((c|0x20)>='a' && (c|0x20)<='f') {  // Hex digit, upper or lower case
    last = Segs[(c|0x20) -'a'+10];
  } else if (c == 12) {                         // Clear display
    clear();
    return 1;
  } else return 1;                              // Other characters don't print
  show(cur, last);
  if (cur < 7) cur++;
  return 1;
}

// Stopwatch Demo **********************************************

SerialDisplay Display;                          // Make a SerialDisplay instance

unsigned long Start = millis();

void setup() {
 SPI.begin();
 pinMode(cs,OUTPUT);
 Display.init();
}

void loop() {
   int split = 1;
   unsigned long now = (millis() - Start)/10;
   int mins = (now/6000) % 60;
   int secs = (now/100) % 60;
   int centis = now % 100;
   Display.printf("%d %02d.%02d.%02d\n", split, mins, secs, centis);
   while ((millis() - Start)/10 == now);
}