// Code to copy a MCM font file to the Arduino + Max7456 OSD
//
// MAX7456_font Sketch
// at 9600 baud it take about 3min to download a mcm file
// http://www.maxim-ic.com/tools/evkit/index.cfm?EVKit=558
// max7456 evaluation kit software

#define DATAOUT 11//11-MOSI
#define DATAIN  12//12-MISO 
#define SPICLOCK  13//13-sck
#define MAX7456SELECT 6 //6
#define USBSELECT 10//10-ss
#define VSYNC 2// INT0

//MAX7456 opcodes
#define VM0_reg   0x00
#define VM1_reg   0x01
#define DMM_reg   0x04
#define DMAH_reg  0x05
#define DMAL_reg  0x06
#define DMDI_reg  0x07
#define CMM_reg   0x08
#define CMAH_reg  0x09
#define CMAL_reg  0x0A
#define CMDI_reg  0x0B
#define STAT_reg  0xA0

//MAX7456 commands
#define CLEAR_display 0x04
#define CLEAR_display_vert 0x06
#define END_string 0xff
#define WRITE_nvr 0xa0
// with NTSC
#define ENABLE_display 0x08
#define ENABLE_display_vert 0x0c
#define MAX7456_reset 0x02
#define DISABLE_display 0x00

// with PAL
// all VM0_reg commands need bit 6 set
//#define ENABLE_display 0x48
//#define ENABLE_display_vert 0x4c
//#define MAX7456_reset 0x42
//#define DISABLE_display 0x40

#define WHITE_level_80 0x03
#define WHITE_level_90 0x02
#define WHITE_level_100 0x01
#define WHITE_level_120 0x00

#define MAX_font_rom 0xff
#define STATUS_reg_nvr_busy 0x20
#define NVM_ram_size 0x36

// with NTSC
#define MAX_screen_rows 0x0d //13

// with PAL
//#define MAX_screen_rows 0x10 //16

volatile byte screen_buffer[MAX_font_rom];
volatile byte character_bitmap[0x40];
volatile byte ascii_binary[0x08];

volatile byte bit_count;
volatile byte byte_count;
volatile int font_count;
volatile int  incomingByte;
volatile int  count;


//////////////////////////////////////////////////////////////
void setup()
{
  byte spi_junk;
  int x;
  Serial.begin(38400);
  Serial.flush();

  digitalWrite(USBSELECT,HIGH); //disable USB chip

  pinMode(MAX7456SELECT,OUTPUT);
  digitalWrite(MAX7456SELECT,HIGH); //disable device

  pinMode(DATAOUT, OUTPUT);
  pinMode(DATAIN, INPUT);
  pinMode(SPICLOCK,OUTPUT);
  pinMode(VSYNC, INPUT);

  // SPCR = 01010000
  //interrupt disabled,spi enabled,msb 1st,master,clk low when idle,
  //sample on leading edge of clk,system clock/4 rate (4 meg)
  SPCR = (1<<SPE)|(1<<MSTR);
  spi_junk=SPSR;
  spi_junk=SPDR;
  delay(250);

  // force soft reset on Max7456
  digitalWrite(MAX7456SELECT,LOW);
  spi_transfer(VM0_reg);
  spi_transfer(MAX7456_reset);
  digitalWrite(MAX7456SELECT,HIGH);
  delay(500);

  // set all rows to same character white level, 90%
  digitalWrite(MAX7456SELECT,LOW);
  for (x = 0; x < MAX_screen_rows; x++)
  {
    spi_transfer(x + 0x10);
    spi_transfer(WHITE_level_90);
  }

  // make sure the Max7456 is enabled
  spi_transfer(VM0_reg);
  spi_transfer(ENABLE_display);
  digitalWrite(MAX7456SELECT,HIGH);

  incomingByte = 0;
  count = 0;
  bit_count = 0;
  byte_count = 0;
  font_count = 0;

  //display all 256 internal MAX7456 characters
  for (x = 0; x < MAX_font_rom; x++)
  {
    screen_buffer[x] = x;
  }
   count = MAX_font_rom;
   write_new_screen();  

  Serial.println("Ready for text file download");
  Serial.println("");
  delay(100);  
}

//////////////////////////////////////////////////////////////
void loop()
{
  byte x;
  
  if (Serial.available() > 0)
  {
    // read the incoming byte:
    incomingByte = Serial.read();

    switch(incomingByte) // parse and decode mcm file
    {
      case 0x0d: // carridge return, end of line
        //Serial.println("cr");
       if (bit_count == 8 && (ascii_binary[0] == 0x30 || ascii_binary[0] == 0x31))
       {
          // turn 8 ascii binary bytes to single byte '01010101' = 0x55
          // fill in 64 bytes of character data
         character_bitmap[byte_count] = decode_ascii_binary();
         byte_count++;
         bit_count = 0;
       }
       else
         bit_count = 0;
      break;
      case 0x0a: // line feed, ignore
        //Serial.println("ln");   
      break;
      case 0x30: // ascii '0'
      case 0x31: // ascii '1' 
        ascii_binary[bit_count] = incomingByte;
        bit_count++;
      break;
      default:
      break;
    }
  }
  
  // we have one completed character
  // write the character to NVM 
  if(byte_count == 64)
  {
    write_NVM();    
    byte_count = 0;
    font_count++;
  }

  // we have burned all 256 characters in NVM
  if(font_count == 256)
  {
    font_count = 0;

    // force soft reset on Max7456
    digitalWrite(MAX7456SELECT,LOW);
    spi_transfer(VM0_reg);
    spi_transfer(MAX7456_reset);
    digitalWrite(MAX7456SELECT,HIGH);
    delay(500);

   // display all 256 new internal MAX7456 characters
   for (x = 0; x < MAX_font_rom; x++)
   {
      screen_buffer[x] = x;
   }
    count = MAX_font_rom;
    write_new_screen(); 
    
    Serial.println("");
    Serial.println("Done with file download");
  }
}

//////////////////////////////////////////////////////////////
byte spi_transfer(volatile byte data)
{
  SPDR = data;                    // Start the transmission
  while (!(SPSR & (1<<SPIF)))     // Wait the end of the transmission
  {
  };
  return SPDR;                    // return the received byte
}

//////////////////////////////////////////////////////////////
void write_new_screen()
{
  int x, local_count;
  byte char_address_hi, char_address_lo;
  byte screen_char;
  
  local_count = count;
  
  char_address_hi = 0;
  char_address_lo = 60; // start on third line
 //Serial.println("write_new_screen");   

  // clear the screen
  digitalWrite(MAX7456SELECT,LOW);
  spi_transfer(DMM_reg);
  spi_transfer(CLEAR_display);
  digitalWrite(MAX7456SELECT,HIGH);

  // disable display
  digitalWrite(MAX7456SELECT,LOW);
  spi_transfer(VM0_reg); 
  spi_transfer(DISABLE_display);

  spi_transfer(DMM_reg); //dmm
  //spi_transfer(0x21); //16 bit trans background
  spi_transfer(0x01); //16 bit trans w/o background

  spi_transfer(DMAH_reg); // set start address high
  spi_transfer(char_address_hi);

  spi_transfer(DMAL_reg); // set start address low
  spi_transfer(char_address_lo);

  x = 0;
  while(local_count) // write out full screen
  {
    screen_char = screen_buffer[x];
    spi_transfer(DMDI_reg);
    spi_transfer(screen_char);
    x++;
    local_count--;
  }

  spi_transfer(DMDI_reg);
  spi_transfer(END_string);

  spi_transfer(VM0_reg); // turn on screen next vertical
  spi_transfer(ENABLE_display_vert);
  digitalWrite(MAX7456SELECT,HIGH);
}

//////////////////////////////////////////////////////////////
byte decode_ascii_binary()
{
  byte ascii_byte;

  ascii_byte = 0;
  
  if (ascii_binary[0] == 0x31) // ascii '1'
    ascii_byte = ascii_byte + 128;

  if (ascii_binary[1] == 0x31)
    ascii_byte = ascii_byte + 64;

  if (ascii_binary[2] == 0x31)
    ascii_byte = ascii_byte + 32;

  if (ascii_binary[3] == 0x31)
    ascii_byte = ascii_byte + 16;

  if (ascii_binary[4] == 0x31)
    ascii_byte = ascii_byte + 8;

  if (ascii_binary[5] == 0x31)
    ascii_byte = ascii_byte + 4;

  if (ascii_binary[6] == 0x31)
    ascii_byte = ascii_byte + 2;

  if (ascii_binary[7] == 0x31)
    ascii_byte = ascii_byte + 1;

  //Serial.print(ascii_byte, HEX);

  return(ascii_byte);
}

//////////////////////////////////////////////////////////////
void write_NVM()
{
  byte x;
  byte char_address_hi, char_address_lo;
  byte screen_char;

  char_address_hi = font_count;
  char_address_lo = 0;
 //Serial.println("write_new_screen");   

  // disable display
  digitalWrite(MAX7456SELECT,LOW);
  spi_transfer(VM0_reg); 
  spi_transfer(DISABLE_display);

  spi_transfer(CMAH_reg); // set start address high
  spi_transfer(char_address_hi);

  for(x = 0; x < NVM_ram_size; x++) // write out 54 (out of 64) bytes of character to shadow ram
  {
    screen_char = character_bitmap[x];
    spi_transfer(CMAL_reg); // set start address low
    spi_transfer(x);
    spi_transfer(CMDI_reg);
    spi_transfer(screen_char);
  }

  // transfer a 54 bytes from shadow ram to NVM
  spi_transfer(CMM_reg);
  spi_transfer(WRITE_nvr);
  
  // wait until bit 5 in the status register returns to 0 (12ms)
  while ((spi_transfer(STAT_reg) & STATUS_reg_nvr_busy) != 0x00);

  spi_transfer(VM0_reg); // turn on screen next vertical
  spi_transfer(ENABLE_display_vert);
  digitalWrite(MAX7456SELECT,HIGH);  
}