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This compiler directive will force the compiler to create an interrupt vector table(IVR).








By default an IVR is always created for normal applications. There is no good reason not to create an IVR for a normal application.

When making a boot loader application things are different. A boot loader application resides in upper flash memory inside the boot area. And when the boot loader applications runs, it has special rights so it can update the flash memory which resides in the lower flash memory.

The boot loader area size depends on the processor but is usual small. An interrupt vector table can use up to 250 bytes or more and it would be a waste of space in many cases. So by default the $LOADER directive which is used to create a boot loader application, will not create an IVR. The downside is that when you do not have an IVR you can not use interrupts.


The $BOOTVECTOR directive will force the compiler to create an IVR when the $LOADER directive is used. This way your boot loader application will include an IVR and you can use interrupts in your code.


noticeThe $BOOTVECTOR directive will only work when the processor has an option to move the IVR to the boot area using the IVSEL bit.


By default the interrupts are located after address 0. Address 0 is the reset vector and usually contains a jump to the real code. Behind the reset address, a table with jumps to the interrupt routines is located. That the code contains an IVR is not enough : in case of a boot loader the interrupt table must be moved to the boot area. For this purpose most processors have a register and bit to switch the IVR between the normal address 0 and the boot loader address.


In BASCOM you can use : Config Intvectorselection = Enabled to set the selection to the boot area.

When the boot loader application finishes, it is best to use a watchdog timeout to reset the processor so the intvector selection is set to the default address 0.

Or you can use Config Intvectorselection = Disabled in your main (normal) application before you enable the interrupts.


So in short you only need to add the $BOOTVECTOR directive and Config Intvectorselection = Enabled to your code. And do not forget to switch back the intvectorselection in the main application!




See also





'                          (c) 1995-2016, MCS
'                        BootEDB-IVSEL.bas
'  This Bootloader is for the BASCOM-EDB
'                IMPORTANT :
' When changing the vector table in the boot loader you MUST
' reset the vector table in your code using :
'       Config Intvectorselection = Disabled
' otherwise your code points to the wrong table
'The loader is supported by the IDE
$prog &HFF , &HE2 , &HDF , &HF8                             ' generated. Take care that the chip supports all fuse bytes.'----------------------------------------------------------------
$crystal = 8000000
$baud = 38400                                               'this loader uses serial com
'It is VERY IMPORTANT that the baud rate matches the one of the boot loader
'do not try to use buffered com as we can not use interrupts
'This bootloader uses buffers serial input
Config Serialin = Buffered , Size = 250
'in order to use interrupts in a bootloader, the processor must support IVSEL
'since the vector table occupies space some processors will not support it.
$bootvector                                                 ' put int table into bootloader section so we can use interrupts
Config Intvectorselection = Enabled                         ' enabled means that the vector table points to the boot section
'since this boot loader uses interrupts we need to activate them but :
'AFTER the interrupt vector table is enabled
Enable Interrupts
$regfile = "m88def.dat"
Const Loaderchip = 88
#if Loaderchip = 88                                         'Mega88
$loader = $c00                                           'this address you can find in the datasheet
'the loader address is the same as the boot vector address
Const Maxwordbit = 5
Const Maxpages = 96 - 1                                 ' total WORD pages  available for program
Config Com1 = Dummy , Synchrone = 0 , Parity = None , Stopbits = 1 , Databits = 8 , Clockpol = 0
Const Maxword =(2 ^ Maxwordbit) * 2                         '128
Const Maxwordshift = Maxwordbit + 1
Const Cdbg = 0                                             ' leave this to 0
#if Cdbg
Print Maxword
Print Maxwordshift
'   Print Maxpages
'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
'Mega 88 : 32 words, 128 pages
'in this loader we may not disable interrupts !
'Disable Interrupts                                          'we do not use ints
'Waitms 100                                                  'wait 100 msec sec
'We start with receiving a file. The PC must send this binary file
'some constants used in serial com
Const Nak = &H15
Const Cack = &H06
Const Can = &H18
'we use some leds as indication in this sample , you might want to remove it
Config Pind.7 = Output
Portd.7 = 0
$timeout = 200000                                           '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
#if Cdbg
  Print "Try " ; Bretries
  Print "Wait"
 Bstatus = Waitkey()                                         'wait for the loader to send a byte
#if Cdbg
  Print "Got "
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 Portd.7 : Waitms 100
#if Cdbg
  Print "RESET"
Goto _reset                                                 'goto the normal reset vector at address 0
'this is the loader routine. It is a Xmodem-checksum reception routine
#if Cdbg
  Print "Clear buffer"
   Bstatus = Waitkey()
Loop Until Bstatus = 0
For J = 1 To 3                                           'this is a simple indication that we start the normal reset vector
  Toggle Portd.7 : Waitms 250
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
   Bblocklocal = 1
   Bstarted = 0                                             ' we were not started yet
   Csum = 0                                                 'checksum is 0 when we start
  Print Chr(nak);                                           ' firt time send a nack
     Bstatus = Waitkey()                                     'wait for statuse 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)
         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(cack);                         'acknowledge
            Incr Bblocklocal                         'increase local block count
          Else                                         'no match so send nak
            Print Chr(nak);
          End If
          Print Chr(nak);                             'blocks do not match
        End If
      Case 4:                                             ' end of transmission , file is transmitted
        If Wrd > 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
        Print Chr(cack);                               ' send ack and ready
        Portd.7 = 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
  If Bretries > 0 Then                                     'attempte left?
    Waitms 1000
    Decr Bretries                                         'decrease attempts
    Goto _reset                                           'reset chip
  End If
'write one or more pages
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
      If Page < Maxpages Then                           'only if we are not erasing the bootspace
         Page = Page + 1                               'next page
         Spmcrval = 3 : Gosub Do_spm                   ' erase  next page
         Spmcrval = 17 : Gosub Do_spm                   ' re-enable page
        Portd.7 = 0 : Waitms 200
      End If
    End If
Else                                                       'eeprom
  For J = 1 To 128
    Writeeeprom Buf(j) , Wrd
     Wrd = Wrd + 1
End If
Toggle Portd.7 : Waitms 10 : Toggle Portd.7               'indication that we write
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 Loaderchip = 128
  !     lds r24,{Z+2}
  !     sts rampz,r24                                       ' we need to set rampz also for the M128
Spmcsr = Spmcrval                                         'assign register
! spm                                                     'this is an asm instruction
! nop
! nop
'How you need to use this program:
'1- compile this program
'2- program into chip with sample elctronics programmer
'3- select MCS Bootloader from programmers
'4- compile a new program for example M88.bas
'5- press F4 and reset your micro
' the program will now be uploaded into the chip with Xmodem Checksum
' you can write your own loader.too
'A stand alone command line loader is also available