'----------------------------------------------------------------
'                          (c) 1995-2020, MCS
'                        Bootloader-Xtiny.bas
'  This sample demonstrates how you can write your own bootloader
'  in BASCOM BASIC for the XTINY
' The xtiny has a different memory lay out
' Normal AVR starts with normal application code and the boot code is placed at the end of memory.
' XTINY starts with BOOT memory. So we always start in BOOT mode.
' With the BOOTEND fuse we can set the size of the BOOT area.
'  A value of 1 will give a size of 256 bytes, a value of 2 gives 512 bytes, etc.
'  In this example we use less than 1024 bytes so we set the fuse to 4.

' After the optional boot space there is the APPLICATION CODE
' And after the APPLICATION CODE there is the APPLICATION DATA
' When you dont want a boot loader you set the bootend fuse to 0.
'  your app will use the boot and application code
' When you want a boot loader, you determine the size of the boot loader and then
'  set the fuse to the proper size
' With a boot loader, the code simply checks if the #123 data is received.
' If so, it starts the loading. If not it continues.
' It is similar to the normal AVR boot loading. The normal AVR boot starts after the normal space.
' # There is one important difference. With normal AVR all the code start at &H0000.
'   For the loader we then use the $LOADER directive to place the code at the proper address
' For XTINY the boot loader starts at &H0000 thus is considred a normal application without specific switches
' Your normal code must now be located after the bootloader. This means you need to instruct the compiler to place the code
' at a different address. We use $ROMSTART for this purpose.
' Remember that AVR has word address. WHich means that each address uses 2 bytes of memory.
'-----------------------------------------------------------------

$regfile = "atxtiny816.dat"
$crystal = 20000000
$hwstack = 40
$swstack = 40
$framesize = 40

Config Sysclock = 20mhz , Prescale = 1
Config Com1 = 115200 , Mode = Asynchroneous , Parity = None , Databits = 8 , Stopbits = 1

Const Page_size = 64                                        'page size is 64
Const Num_pages = 128                                       'number of page is 128

'It is VERY IMPORTANT that the baud rate matches the one of the boot loader
'do not try to use buffered com since we do not use interrupts

'possible return codes of the PC bootloader.exe
' -6005    Cancel requested
' -6006    Fatal time out
' -6007    Unrecoverable event during protocol
' -6008    Too many errors during protocol
' -6009    Block sequence error in Xmodem
' -6016    Session aborted

'since this is a boot loader we do not want a vector table
'we reduce the vector table to 0
$reduceivr

'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 , Wptr As Word

'Disable Interrupts                                          'we do not use ints

'We start with receiving a file. The PC must send this binary file

'some constants used in serial com
Const Cnak = &H15
Const Cack = &H06

$timeout = 400000                                           'we use a timeout
'When you get LOADER errors during the upload, increase the timeout value
'for example at 16 Mhz, use 200000

Bretries = 5                                                'we try 5 times
Do
   Bstatus = Waitkey()                                      'wait for the loader to send a byte
   Print Chr(bstatus);                                      'echo back

   If Bstatus = 123 Then                                       'did we received value 123 ?
      Goto Loader                                           'jump into boot loader
   End If
   Decr Bretries
Loop Until Bretries = 0

'if we arrive here, there was not boot character received. we simply continue
Goto Application_start_noload                               'goto the normal code


'this is the loader routine. It is a Xmodem-checksum reception routine
Loader:
   Do
      Bstatus = Waitkey()                                   ' flush the data
   Loop Until Bstatus = 0

   Bretries = 10                                            ' number of retries
   Wptr = &H8400                                            ' mapped memory uses byte address and starts at &H8000
                                                            ' we add the max size of the loader to it since that is where the normal code will be written to
   Do
      Bblocklocal = 1
      Csum = 0                                              ' checksum is 0 when we start
      Print Chr(cnak);                                      ' firt time send a nack
      Do

         Bstatus = Waitkey()                                ' wait for status byte

         Select Case Bstatus
            Case 1:                                         ' start of heading, PC is ready to send
               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 Writepages                       ' yes go write the page
                     Print Chr(cack);                       ' acknowledge
                     Incr Bblocklocal                       ' increase local block count
                  Else                                      ' no match so send nak
                     Print Chr(cnak);
                  End If
               Else
                  Print Chr(cnak);                          ' blocks do not match
               End If
            Case 4:                                              ' end of transmission , file is transmitted
            '  Waitms 100                                   ' OPTIONAL REMARK THIS IF THE DTR SIGNAL ARRIVES TO EARLY
               Print Chr(cack);                             ' send ack and ready
               Waitms 20
               Goto Application_start                       ' start new program
            Case &H18:                                      ' PC aborts transmission
               Goto Application_start                       ' ready
            Case 123 : Exit Do                              ' was probably still in the buffer
            Case Else
               Exit Do                                      ' no valid data
         End Select
      Loop
      If Bretries > 0 Then                                  ' attempte left?
         Waitms 1000
         Decr Bretries                                      ' decrease attempts
      Else
         Exit Do                                            ' reset chip
      End If
   Loop

Application_start:
   Cpu_ccp = &HD8
   Rstctrl_swrr = 1                                         ' perform a soft reset

'no code between the label above and below !

Application_start_noload:
   Nvmctrl_ctrlb.nvmctrl_bootlock_bp = 1                    ' enable boot section lock
   Goto &H200                                               ' normal app code

'this sub routine will write the pages
Writepages:
   For J = 1 To 128                                         ' get 128 bytes
      Out Wptr , Buf(j)                                     ' write to mapped memory page
      Incr Wptr                                             ' increase pointer
      If J = 64 Then                                        ' do the page write here
         Gosub Page_erase_write
      End If
   Next

   'walk into this code so the second page gets written too
Page_erase_write:
   Cpu_ccp = &H9D
   Nvmctrl_ctrla = 3                                        'Erase and write page
   Bitwait Nvmctrl_status.nvmctrl_fbusy_bp , Reset
Return

'this loader takes less than 1024 bytes so the BOOT FUSE is set to 4.
'do NOT FORGET that your normal app must use $ROMSTART=&H200 in that case  : halve of the bytes size of the loader

'one other thing : the reset pin works in UPDI mode by default. so your chip will not reset when you do not change the fuse
'but there are other ways of reset such as soft reset, bod and wd.
 

$regfile = "m1284pdef.dat"
$crystal = 20000000
$baud = 19200
$hwstack = 32                                               ' default use 32 for the hardware stack
$swstack = 10                                               'default use 10 for the SW stack
$framesize = 40                                             'default use 40 for the frame space

dim I as byte
Dim S As String * 4
Dim Sa(5) As Byte At S Overlay
Dim Scd As Double
Dim Sc(8) As Byte At Scd Overlay
Dim Fd As Word At Sc(1) Overlay

' scd=4251398078363129640 dont cut and paste from windows calculator! se mws below
scd=123456

Print "word overlay'"
Print Hex(fd)
Print "double "
Print Hex(scd)
Print "array elements 8 to 1"
For I = 8 To 1 Step -1
Print Hex(sc(i)) ;
Next


S = "text"
Print
For I = 1 To 5
   Print Chr(sa(i));
Next

End