/* Tiny Terminal 2 v2 - see http://www.technoblogy.com/show?2D8S

   David Johnson-Davies - www.technoblogy.com - 16th December 2018
   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/
*/

// ATtiny85 Pins
int const dc = 1;
int const clk = 2;
int const data = 3;
int const cs = 4;
int const serial = 0;

// Character set - stored in program memory
const uint8_t CharMap[96][6] PROGMEM = {
{ 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 }, 
{ 0x00, 0x00, 0x5F, 0x00, 0x00, 0x00 }, 
{ 0x00, 0x07, 0x00, 0x07, 0x00, 0x00 }, 
{ 0x14, 0x7F, 0x14, 0x7F, 0x14, 0x00 }, 
{ 0x24, 0x2A, 0x7F, 0x2A, 0x12, 0x00 }, 
{ 0x23, 0x13, 0x08, 0x64, 0x62, 0x00 }, 
{ 0x36, 0x49, 0x56, 0x20, 0x50, 0x00 }, 
{ 0x00, 0x08, 0x07, 0x03, 0x00, 0x00 }, 
{ 0x00, 0x1C, 0x22, 0x41, 0x00, 0x00 }, 
{ 0x00, 0x41, 0x22, 0x1C, 0x00, 0x00 }, 
{ 0x2A, 0x1C, 0x7F, 0x1C, 0x2A, 0x00 }, 
{ 0x08, 0x08, 0x3E, 0x08, 0x08, 0x00 }, 
{ 0x00, 0x80, 0x70, 0x30, 0x00, 0x00 }, 
{ 0x08, 0x08, 0x08, 0x08, 0x08, 0x00 }, 
{ 0x00, 0x00, 0x60, 0x60, 0x00, 0x00 }, 
{ 0x20, 0x10, 0x08, 0x04, 0x02, 0x00 }, 
{ 0x3E, 0x51, 0x49, 0x45, 0x3E, 0x00 }, 
{ 0x00, 0x42, 0x7F, 0x40, 0x00, 0x00 }, 
{ 0x72, 0x49, 0x49, 0x49, 0x46, 0x00 }, 
{ 0x21, 0x41, 0x49, 0x4D, 0x33, 0x00 }, 
{ 0x18, 0x14, 0x12, 0x7F, 0x10, 0x00 }, 
{ 0x27, 0x45, 0x45, 0x45, 0x39, 0x00 }, 
{ 0x3C, 0x4A, 0x49, 0x49, 0x31, 0x00 }, 
{ 0x41, 0x21, 0x11, 0x09, 0x07, 0x00 }, 
{ 0x36, 0x49, 0x49, 0x49, 0x36, 0x00 }, 
{ 0x46, 0x49, 0x49, 0x29, 0x1E, 0x00 }, 
{ 0x00, 0x00, 0x14, 0x00, 0x00, 0x00 }, 
{ 0x00, 0x40, 0x34, 0x00, 0x00, 0x00 }, 
{ 0x00, 0x08, 0x14, 0x22, 0x41, 0x00 }, 
{ 0x14, 0x14, 0x14, 0x14, 0x14, 0x00 }, 
{ 0x00, 0x41, 0x22, 0x14, 0x08, 0x00 }, 
{ 0x02, 0x01, 0x59, 0x09, 0x06, 0x00 }, 
{ 0x3E, 0x41, 0x5D, 0x59, 0x4E, 0x00 }, 
{ 0x7C, 0x12, 0x11, 0x12, 0x7C, 0x00 }, 
{ 0x7F, 0x49, 0x49, 0x49, 0x36, 0x00 }, 
{ 0x3E, 0x41, 0x41, 0x41, 0x22, 0x00 }, 
{ 0x7F, 0x41, 0x41, 0x41, 0x3E, 0x00 }, 
{ 0x7F, 0x49, 0x49, 0x49, 0x41, 0x00 }, 
{ 0x7F, 0x09, 0x09, 0x09, 0x01, 0x00 }, 
{ 0x3E, 0x41, 0x41, 0x51, 0x73, 0x00 }, 
{ 0x7F, 0x08, 0x08, 0x08, 0x7F, 0x00 }, 
{ 0x00, 0x41, 0x7F, 0x41, 0x00, 0x00 }, 
{ 0x20, 0x40, 0x41, 0x3F, 0x01, 0x00 }, 
{ 0x7F, 0x08, 0x14, 0x22, 0x41, 0x00 }, 
{ 0x7F, 0x40, 0x40, 0x40, 0x40, 0x00 }, 
{ 0x7F, 0x02, 0x1C, 0x02, 0x7F, 0x00 }, 
{ 0x7F, 0x04, 0x08, 0x10, 0x7F, 0x00 }, 
{ 0x3E, 0x41, 0x41, 0x41, 0x3E, 0x00 }, 
{ 0x7F, 0x09, 0x09, 0x09, 0x06, 0x00 }, 
{ 0x3E, 0x41, 0x51, 0x21, 0x5E, 0x00 }, 
{ 0x7F, 0x09, 0x19, 0x29, 0x46, 0x00 }, 
{ 0x26, 0x49, 0x49, 0x49, 0x32, 0x00 }, 
{ 0x03, 0x01, 0x7F, 0x01, 0x03, 0x00 }, 
{ 0x3F, 0x40, 0x40, 0x40, 0x3F, 0x00 }, 
{ 0x1F, 0x20, 0x40, 0x20, 0x1F, 0x00 }, 
{ 0x3F, 0x40, 0x38, 0x40, 0x3F, 0x00 }, 
{ 0x63, 0x14, 0x08, 0x14, 0x63, 0x00 }, 
{ 0x03, 0x04, 0x78, 0x04, 0x03, 0x00 }, 
{ 0x61, 0x59, 0x49, 0x4D, 0x43, 0x00 }, 
{ 0x00, 0x7F, 0x41, 0x41, 0x41, 0x00 }, 
{ 0x02, 0x04, 0x08, 0x10, 0x20, 0x00 }, 
{ 0x00, 0x41, 0x41, 0x41, 0x7F, 0x00 }, 
{ 0x04, 0x02, 0x01, 0x02, 0x04, 0x00 }, 
{ 0x40, 0x40, 0x40, 0x40, 0x40, 0x00 }, 
{ 0x00, 0x03, 0x07, 0x08, 0x00, 0x00 }, 
{ 0x20, 0x54, 0x54, 0x78, 0x40, 0x00 }, 
{ 0x7F, 0x28, 0x44, 0x44, 0x38, 0x00 }, 
{ 0x38, 0x44, 0x44, 0x44, 0x28, 0x00 }, 
{ 0x38, 0x44, 0x44, 0x28, 0x7F, 0x00 }, 
{ 0x38, 0x54, 0x54, 0x54, 0x18, 0x00 }, 
{ 0x00, 0x08, 0x7E, 0x09, 0x02, 0x00 }, 
{ 0x18, 0xA4, 0xA4, 0x9C, 0x78, 0x00 }, 
{ 0x7F, 0x08, 0x04, 0x04, 0x78, 0x00 }, 
{ 0x00, 0x44, 0x7D, 0x40, 0x00, 0x00 }, 
{ 0x20, 0x40, 0x40, 0x3D, 0x00, 0x00 }, 
{ 0x7F, 0x10, 0x28, 0x44, 0x00, 0x00 }, 
{ 0x00, 0x41, 0x7F, 0x40, 0x00, 0x00 }, 
{ 0x7C, 0x04, 0x78, 0x04, 0x78, 0x00 }, 
{ 0x7C, 0x08, 0x04, 0x04, 0x78, 0x00 }, 
{ 0x38, 0x44, 0x44, 0x44, 0x38, 0x00 }, 
{ 0xFC, 0x18, 0x24, 0x24, 0x18, 0x00 }, 
{ 0x18, 0x24, 0x24, 0x18, 0xFC, 0x00 }, 
{ 0x7C, 0x08, 0x04, 0x04, 0x08, 0x00 }, 
{ 0x48, 0x54, 0x54, 0x54, 0x24, 0x00 }, 
{ 0x04, 0x04, 0x3F, 0x44, 0x24, 0x00 }, 
{ 0x3C, 0x40, 0x40, 0x20, 0x7C, 0x00 }, 
{ 0x1C, 0x20, 0x40, 0x20, 0x1C, 0x00 }, 
{ 0x3C, 0x40, 0x30, 0x40, 0x3C, 0x00 }, 
{ 0x44, 0x28, 0x10, 0x28, 0x44, 0x00 }, 
{ 0x4C, 0x90, 0x90, 0x90, 0x7C, 0x00 }, 
{ 0x44, 0x64, 0x54, 0x4C, 0x44, 0x00 }, 
{ 0x00, 0x08, 0x36, 0x41, 0x00, 0x00 }, 
{ 0x00, 0x00, 0x77, 0x00, 0x00, 0x00 }, 
{ 0x00, 0x41, 0x36, 0x08, 0x00, 0x00 }, 
{ 0x02, 0x01, 0x02, 0x04, 0x02, 0x00 }, 
{ 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00 }
};

void Send (uint8_t d) {  
  for (uint8_t bit = 0x80; bit; bit >>= 1) {
    PINB = 1<<clk;                        // clk low
    if (d & bit) PORTB = PORTB | (1<<data); else PORTB = PORTB & ~(1<<data);
    PINB = 1<<clk;                        // clk high
  }
}

void InitDisplay () {
  PINB = 1<<dc | 1<<cs;                   // dc and cs low
  Send(0x81);
  Send(0xC0);                             // Increase contrast
  Send(0xAF);                             // Display on
  PINB = 1<<dc | 1<<cs;                   // dc and cs high
}

// Character terminal **********************************************

int Line, Column, Scroll;
uint8_t Grey = 0xF;                       // Grey level; 0 to 15

#define clk128 clk16 clk16 clk16 clk16 clk16 clk16 clk16 clk16
#define clk16 clk2 clk2 clk2 clk2 clk2 clk2 clk2 clk2
#define clk2 PINB=1<<clk;PINB=1<<clk;PINB=1<<clk;PINB=1<<clk;

// Optimised for fast scrolling
void ClearLine (int line) {
  PINB = 1<<dc | 1<<cs;                   // dc and cs low
  Send(0x00); Send(0x10);                 // Column start
  Send(0xB0); Send(line<<3);              // Row start
  PINB = 1<<dc;                           // dc high
  for (uint8_t i=0; i<32; i++) {
    clk128 clk128
  }
  PINB = 1<<cs;                           // cs high
}

void ClearDisplay () {
  for (uint8_t p=0; p < 8; p++) ClearLine(p);
  Line = Scroll;
  Column = 0;
}

// Clears the top line, then scrolls the display up by one line
void ScrollDisplay () {
  ClearLine(Scroll);
  Scroll = (Scroll + 1) & 0x07;
  PINB = 1<<dc | 1<<cs;                   // dc and cs low
  Send(0xD3);
  Send(Scroll<<3);
  PINB = 1<<dc | 1<<cs;                   // dc and cs low
}

void PlotChar (char ch, uint8_t line, uint8_t column) {
  ch = ch - 32;
  uint8_t row = (line+Scroll)<<3 ; uint8_t col = column*3;
  PINB = 1<<cs;                           // cs low
  for (uint8_t r = 0 ; r<8; r++) {
    PINB = 1<<dc;                         // dc low
    Send(0x00 + (col & 0x0F));            // Column start low
    Send(0x10 + (col >> 4));              // Column start high
    Send(0xB0); Send((row+r) & 0x3F);     // Row start
    PINB = 1<<dc;                         // dc high
    for (uint8_t c = 0 ; c < 3; c++) {
      int adds = &CharMap[ch][c*2];
      uint8_t hi = pgm_read_byte(adds);
      uint8_t lo = pgm_read_byte(adds + 1);
      uint8_t mask = 1<<r;
      hi = hi & mask ? Grey<<4 : 0;
      lo = lo & mask ? Grey : 0;
      Send(hi | lo);
    }
  }
  PINB = 1<<cs;                           // cs high
}

// Prints a character, handling control characters
void Print (char c) {
  c = c & 0x7F;                           // Ignore top bit
  if (c >= 32) {
    PlotChar(c, Line, Column++);
    if (Column > 41) {
      Column = 0;
      if (Line == 7) ScrollDisplay(); else Line++;
    }
  } else if (c >= 0x11 && c <= 0x14) {    // Greyscale
    Grey = (1<<(c & 7))-1;
  } else if (c == 13) {                   // Return character
    Column = 0;
    if (Line == 7) ScrollDisplay(); else Line++;
  }
}

// USI UART **********************************************

unsigned char ReverseByte (unsigned char x) {
  x = ((x >> 1) & 0x55) | ((x << 1) & 0xaa);
  x = ((x >> 2) & 0x33) | ((x << 2) & 0xcc);
  x = ((x >> 4) & 0x0f) | ((x << 4) & 0xf0);
  return x;    
}

// Initialise USI for UART reception.
void InitialiseUSI (void) {  
  DDRB &= ~(1<<serial);           // Define DI as input
  USICR = 0;                      // Disable USI.
  GIFR = 1<<PCIF;                 // Clear pin change interrupt flag.
  GIMSK |= 1<<PCIE;               // Enable pin change interrupts
  PCMSK |= 1<<PCINT0;             // Enable pin change on pin 0
}

// Pin change interrupt detects start of UART reseption.
ISR (PCINT0_vect) {
  if (PINB & 1<<serial) return;   // Ignore if DI is high
  GIMSK &= ~(1<<PCIE);            // Disable pin change interrupts
  TCCR0A = 2<<WGM00;              // Timer in CTC mode
  TCCR0B = 2<<CS00;               // Set prescaler to /8
  OCR0A = 103;                    // Shift every (103+1)*8 cycles
  TCNT0 = 206;                    // Start counting from (256-52+2)
  // Enable USI OVF interrupt, and select Timer0 compare match as USI Clock source:
  USICR = 1<<USIOIE | 0<<USIWM0 | 1<<USICS0;
  USISR = 1<<USIOIF | 8;          // Clear USI OVF flag, and set counter
}

// USI overflow interrupt indicates we've received a byte
ISR (USI_OVF_vect) {
  USICR  =  0;                    // Disable USI         
  int temp = USIDR;
  putBuf(ReverseByte(temp));
  GIFR = 1<<PCIF;                 // Clear pin change interrupt flag.
  GIMSK |= 1<<PCIE;               // Enable pin change interrupts again
}

// Circular buffer **********************************************

int const BufSize = 32;
uint8_t Buffer[BufSize];
int BufStart = 0, BufEnd = 0;

void putBuf (uint8_t byte) {
  if ((BufStart+BufSize-BufEnd) % BufSize == 1) return; // Buffer full
  Buffer[BufEnd] = byte;
  BufEnd = (BufEnd+1) % BufSize;
}

int getBuf () {
  if (BufStart == BufEnd) return -1;                    // Buffer empty
  int temp = Buffer[BufStart];
  BufStart = (BufStart+1) % BufSize;
  return temp;
}

// Setup **********************************************

void setup() {
  pinMode(dc, OUTPUT); digitalWrite(dc,HIGH);
  pinMode(clk, OUTPUT); digitalWrite(clk,HIGH);
  pinMode(data, OUTPUT);
  pinMode(cs, OUTPUT); digitalWrite(cs,HIGH);
  ClearDisplay();
  InitDisplay();
  // Initialise USI UART
  InitialiseUSI();
}

void loop () {
  char temp = getBuf();
  if (temp != -1) Print(temp);
}