//==============================================================================
//
//  Simple PC Keyboard - Driver
//
//==============================================================================
//
//  This firmware source code is for free. You can redistribute, copy and
//  modify it. It is distributed in the hope that it will be useful,
//  but without any warranty.
//
//  Check the applications section of www.avrcard.com for updates and further
//  information on this project.
//
//  Have fun.
//
//  Hans Kallen, www.avrcard.com, August 2003
//
//==============================================================================
//
//  Version  Date       Author  Changes
//  -------  ---------- ------- ------------------------------
//  1.0      03.10.2002 HK      Initial release
//
//  Target:   ATmega128 at 16MHz
//  Compiler: AVRco (by www.e-lab.de)
//
//  Hardware: INT4 - Clock
//            PE.5 - Data
//
//  User program must provide a pipe:    
//     var Keyboard: Pipe[16] of Char;
//  and a process that receives the keyboard chars from that pipe.
//  Procedure InitKeyb must be called before using this driver.
//
//
////////////////////////////////////////////////////////////////////////////////

const
   CodeTab: array[$0..$FF] of Char =
      // unshifted
     (#0,  #0,  #0,  #0,  #0,  #0,  #0, #0, #0,  #0,  #0,  #0,  #0,  #9, '|', #0,
      #0,  #0,  #0,  #0,  #0, 'q', '1', #0, #0,  #0, 'y', 's', 'a', 'w', '2', #0,
      #0, 'c', 'x', 'd', 'e', '4', '3', #0, #0, ' ', 'v', 'f', 't', 'r', '5', #0,
      #0, 'n', 'b', 'h', 'g', 'z', '6', #0, #0, ',', 'm', 'j', 'u', '7', '8', #0,
      #0, ',', 'k', 'i', 'o', '0', '9', #0, #0, '.', '-', 'l', 'ø', 'p', '+', #0,
      #0,  #0, 'æ',  #0, 'å', '^',  #0, #0, #0,  #0, #13, '¨',  #0, '$',  #0, #0,
      #0, '<',  #0,  #0,  #0,  #0,  #8, #0, #0, '1',  #0, '4', '7',  #0,  #0, #0,
      '0',',', '2', '5', '6', '8',  #0, #0, #0,#$60, '3', '-', '*', '9',  #0, #0,

      // shifted
      #0,  #0,  #0,  #0,  #0,  #0,  #0, #0, #0,  #0,  #0,  #0,  #0,  #9, '§', #0,
      #0,  #0,  #0,  #0,  #0, 'Q', '+', #0, #0,  #0, 'Y', 'S', 'A', 'W', '"', #0,
      #0, 'C', 'X', 'D', 'E', '¤', '*', #0, #0, ' ', 'V', 'F', 'T', 'R', '%', #0,
      #0, 'N', 'B', 'H', 'G', 'Z', '&', #0, #0, 'L', 'M', 'J', 'U', '/', '(', #0,
      #0, ';', 'K', 'I', 'O', '=', ')', #0, #0, ':', '_', 'L', 'Ø', 'P', '?', #0,
      #0,  #0, 'Æ',  #0, '!', '`',  #0, #0, #0,  #0, #13, '^', '*', '£',  #0, #0,
      #0, '>',  #0,  #0,  #0,  #0,  #8, #0, #0, '1',  #0, '4', '7',  #0,  #0, #0,
      '0',',', '2', '5', '6', '8',  #0, #0, #0, '+', '3', '-', '*', '9',  #0, #0);

   // Extended keyboard codes = scan code + $80
   kbdPgUp:  Byte = $FD;
   kbdPgDn:  Byte = $FA;
   kbdUp:    Byte = $F5;
   kbdDn:    Byte = $F2;
   kbdLeft:  Byte = $EB;
   kbdRight: Byte = $F4;
   kbdEnter: Byte = $0D;
   kbdSpace: Byte = $20;
   kbdBS:    Byte = $08;
   kbdTab:   Byte = $09;

type
   KeybStat = (up, spec, shift, goup, goupext);
   
var
   // PC keyboard handler
   BitCntr:           Byte;
   tmpByte:           Byte;
   Keyb:              KeybStat;


   
Procedure InitKeyb;
//------------------------------------------------------------------------------
begin
   BitCntr:= 11;
   Keyb:= up;
   PipeFlush (Keyboard);
   // init port interrupt INT4
   incl (EICR,  1);
   excl (EICR,  0);                    // falling edge INT4
   excl (EIFR,  4);                    // reset     INT4
   incl (EIMSK, 4);                    // enable    INT4
end InitKeyb;


Interrupt INT4;
//==============================================================================
begin
   if (BitCntr < 11) and (BitCntr > 2) then    // Bit 3 to 10 is data. Parity bit,
      tmpByte:= tmpByte shr 1;                 // start and stop bits are ignored.
      if (PinE and %00100000) > 0 then
         incl (tmpByte, 7);
      else
         excl (tmpByte, 7);
      endif;
   endif;
   dec (BitCntr);
   if BitCntr = 0 then                    // All bits received
      BitCntr:= 11;
      // Decode scancodes into char
      case Keyb of
         up:      case tmpByte of
                     $E0: Keyb:= spec;  |
                     $F0: Keyb:= goup;  |
                     $12: Keyb:= shift; |
                  else
                     PipeSend (Keyboard, CodeTab [tmpByte]);
                  endcase;  |
            
         shift:   case tmpByte of
                     $F0: Keyb:= goup; |
                  else
                     tmpByte:= tmpByte + $80;  // add offset to code tab
                     PipeSend (Keyboard, CodeTab [tmpByte]);
                     Keyb:= goup;
                  endcase;   |

         goup:    Keyb:= up; |
         
         goupext: case tmpByte of
                     $E0: Keyb:= up; |
                  endcase; |
            
         spec:    case tmpByte of
                     $F0: Keyb:= goup;  |
                     $E0: |
                  else
                     PipeSend (Keyboard, Char (tmpByte + $80));
                  endcase; |

      endcase;  // KeybStat
   endif; // BitCntr = 0
end;