$crystal = 16000000

$baud = 38400       'this loader uses serial com

$regfile = "m2560def.dat"
Const Loaderchip = 2560

#if Loaderchip = 2560       ' Mega2560
    $loader = &H1FC00       ' 1024 words
    Const Maxwordbit = 7       'Z7 is maximum bit                                   '
    Config Com1 = Dummy , Synchrone = 0 , Parity = None , Stopbits = 1 , Databits = 8 , Clockpol = 0
#endif

Const Maxword =(2 ^ Maxwordbit) * 2       '128
Const Maxwordshift = Maxwordbit + 1
Const Cdebug = 0       ' leave this to 0

#if Cdebug
   Print Maxword
   Print Maxwordshift
#endif

'Dim the used variables
Dim Bstatus As Byte , Bretries As Byte , Bblock As Byte , Bblocklocal As Byte
Dim Bcsum1 As Byte , Bcsum2 As Byte , Buf(128) As Byte , Csum As Byte
Dim J As Byte , Spmcrval As Byte       ' self program command byte value

Dim Z As Long       'this is the Z pointer word
Dim Vl As Byte , Vh As Byte       ' these bytes are used for the data values
Dim Wrd As Word , Page As Word       'these vars contain the page and word address
Dim Bkind As Byte , Bstarted As Byte

Disable Interrupts       'we do not use ints

'some constants used in serial com
Const Nak = &H15
Const Ack = &H06
Const Can = &H18

'we use some leds as indication in this sample , you might want to remove it
Config Pinb.2 = Output
Portb.2 = 1       'the stk200 has inverted logic for the leds
Config Pinb.3 = Output
Portb.3 = 1

$timeout = 400000       'we use a timeout

Bretries = 5       'we try 5 times
Testfor123:
#if Cdebug
    Print "Try " ; Bretries
    Print "Wait"
#endif
Bstatus = Waitkey()       'wait for the loader to send a byte
#if Cdebug
   Print "Got "
#endif

Print Chr(bstatus);

If Bstatus = 123 Then       'did we received value 123 ?
   Bkind = 0       'normal flash loader
   Goto Loader
Elseif Bstatus = 124 Then       ' EEPROM
   Bkind = 1       ' EEPROM loader
   Goto Loader
Elseif Bstatus <> 0 Then
   Decr Bretries
   If Bretries <> 0 Then Goto Testfor123       'we test again
End If

For J = 1 To 10       'this is a simple indication that we start the normal reset vector
   Toggle Portb.2 : Waitms 100
Next

#if Cdebug
  Print "RESET"
#endif
Goto _reset       'goto the normal reset vector at address 0

'this is the loader routine. It is a Xmodem-checksum reception routine
Loader:
  #if Cdebug
      Print "Clear buffer"
  #endif
  Do
     Bstatus = Waitkey()
  Loop Until Bstatus = 0

  For J = 1 To 3       'this is a simple indication that we start the normal reset vector
     Toggle Portb.2 : Waitms 50
  Next

  If Bkind = 0 Then
     Spmcrval = 3 : Gosub Do_spm       ' erase  the first page
     Spmcrval = 17 : Gosub Do_spm       ' re-enable page
  End If

Bretries = 10       'number of retries

Do
  Bstarted = 0       ' we were not started yet
  Csum = 0       'checksum is 0 when we start
  Print Chr(nak);       ' firt time send a nack
  Do

    Bstatus = Waitkey()       'wait for statuse byte

    Select Case Bstatus
       Case 1:       ' start of heading, PC is ready to send
            Incr Bblocklocal       'increase local block count
            Csum = 1       'checksum is 1
            Bblock = Waitkey() : Csum = Csum + Bblock       'get block
            Bcsum1 = Waitkey() : Csum = Csum + Bcsum1       'get checksum first byte
            For J = 1 To 128       'get 128 bytes
              Buf(j) = Waitkey() : Csum = Csum + Buf(j)
            Next
            Bcsum2 = Waitkey()       'get second checksum byte
            If Bblocklocal = Bblock Then       'are the blocks the same?
               If Bcsum2 = Csum Then       'is the checksum the same?
                  Gosub Writepage       'yes go write the page
                  Print Chr(ack);       'acknowledge
               Else       'no match so send nak
                  Print Chr(nak);
               End If
            Else
               Print Chr(nak);       'blocks do not match
            End If
       Case 4:       ' end of transmission , file is transmitted
             If Wrd > 0 And Bkind = 0 Then       'if there was something left in the page
                 Wrd = 0       'Z pointer needs wrd to be 0
                 Spmcrval = 5 : Gosub Do_spm       'write page
                 Spmcrval = 17 : Gosub Do_spm       ' re-enable page
             End If
            '  Waitms 100                                   ' OPTIONAL REMARK THIS IF THE DTR SIGNAL ARRIVES TO EARLY
             Print Chr(ack);       ' send ack and ready

             Portb.3 = 0       ' simple indication that we are finished and ok
             Waitms 20
             Goto _reset       ' start new program
       Case &H18:       ' PC aborts transmission
             Goto _reset       ' ready
       Case 123 : Exit Do       'was probably still in the buffer
       Case 124 : Exit Do
       Case Else
          Exit Do       ' no valid data
    End Select
  Loop
  If Bretries > 0 Then       'attempte left?
     Waitms 1000
     Decr Bretries       'decrease attempts
  Else
     Goto _reset       'reset chip
  End If
Loop

'write one or more pages
Writepage:
If Bkind = 0 Then
   For J = 1 To 128 Step 2       'we write 2 bytes into a page
      Vl = Buf(j) : Vh = Buf(j + 1)       'get Low and High bytes
      lds r0, {vl}       'store them into r0 and r1 registers
      lds r1, {vh}
      Spmcrval = 1 : Gosub Do_spm       'write value into page at word address
      Wrd = Wrd + 2       ' word address increases with 2 because LS bit of Z is not used
      If Wrd = Maxword Then       ' page is full
          Wrd = 0       'Z pointer needs wrd to be 0
          Spmcrval = 5 : Gosub Do_spm       'write page
          Spmcrval = 17 : Gosub Do_spm       ' re-enable page

          Page = Page + 1       'next page
          Spmcrval = 3 : Gosub Do_spm       ' erase  next page
          Spmcrval = 17 : Gosub Do_spm       ' re-enable page
      End If
   Next

Else     'eeprom
     For J = 1 To 128
       Writeeeprom Buf(j) , Wrd
       Wrd = Wrd + 1
     Next
End If
Toggle Portb.2 : Waitms 10 : Toggle Portb.2       'indication that we write
Return

Do_spm:
  Bitwait Spmcsr.0 , Reset       ' check for previous SPM complete
  Bitwait Eecr.1 , Reset       'wait for eeprom

  Z = Page       'make equal to page
  Shift Z , Left , Maxwordshift       'shift to proper place
  Z = Z + Wrd       'add word
  lds r30,{Z}
  lds r31,{Z+1}

  #if _romsize > 65536
      lds r24,{Z+2}
      sts rampz,r24       ' we need to set rampz also for the M128
  #endif

  Spmcsr = Spmcrval       'assign register
  spm     'this is an asm instruction
  nop
  nop
Return