Action
Instruct the compiler to create a boot loader at the specified address.
Syntax
$LOADER = address
Remarks
address |
The address where the boot loader is located. You can find this address in the data sheet. |
Most AVR chips have a so called boot section. Normally a chip will start at address 0 when it resets. This is also called the reset vector.
Chips that have a boot section, split the flash memory in two parts. The boot section is a small part of the normal flash and by setting a fuse bit you select that the chip runs code at the boot sector when it resets instead of the normal reset vector.
Some chips also have fuse bits to select the size of the boot loader.
The MCS boot loader sample is a serial boot loader that uses the serial port. It uses the X-modem checksum protocol to receive the data. Most terminal emulators can send X-modem checksum.
The sample is written so it supports all chips with a boot section. You need to do the following :
| • | identify the $regfile directive for your chip |
| • | un-remark the line and the line with the CONST that is used for conditional compilation |
| • | remark all other $regfile lines and CONST lines. |
| • | compile the file |
| • | program the chip |
| • | set the fuse bit so reset is pointed to the boot loader |
| • | set the fuse bit so the boot size is 1024 words |
| • | select the MCS Boot loader programmer. |
The boot loader is written to work at a baud rate of 57600. This works for most chips that use the internal oscillator. But it is best to check it first with a simple program. When you use a crystal you might even use a higher speed.
Do not forget that the MCS boot loader must be set to the same baud rate as the boot loader program.
Now make a new test program and compile it. Press F4 to start the MCS boot loader. You now need to reset the chip so that it will start the boot loader section. The boot loader will send a byte with value of 123 and the Bascom boot loader receives this and thus starts the loader process.
There will be a stand alone boot loader available too. And the sample will be extended to support other AVR chips with boot section too.
There is a $BOOT directive too. It is advised to use $LOADER as it allows you to write the boot loader in BASIC.
You can not use interrupts in your boot loader program as the interrupts will point to the reset vector which is located in the lower section of the flash. When you start to writing pages, you overwrite this part.
See also
Example
'----------------------------------------------------------------
' (c) 1995-2005, MCS
' Bootloader.bas
' This sample demonstrates how you can write your own bootloader
' in BASCOM BASIC
'-----------------------------------------------------------------
'This sample will be extended to support other chips with bootloader
'The loader is supported from the IDE
'$regfile = "m88def.dat"
'Const Loader = 88
'$regfile = "m32def.dat"
'Const Loaderchip = 32
'$regfile = "m88def.dat"
'Const Loaderchip = 88
$regfile = "m162def.dat"
Const Loaderchip = 162
#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
Config Com1 = Dummy , Synchrone = 0 , Parity = None , Stopbits = 1 , Databits = 8 , Clockpol = 0
#endif
#if Loaderchip = 32 ' Mega32
$loader = $3c00 ' 1024 words
Const Maxwordbit = 6 'Z6 is maximum bit '
Config Com1 = Dummy , Synchrone = 0 , Parity = None , Stopbits = 1 , Databits = 8 , Clockpol = 0
#endif
#if Loaderchip = 8 ' Mega8
$loader = $c00 ' 1024 words
Const Maxwordbit = 5 'Z5 is maximum bit '
Config Com1 = Dummy , Synchrone = 0 , Parity = None , Stopbits = 1 , Databits = 8 , Clockpol = 0
#endif
#if Loaderchip = 161 ' Mega161
$loader = $1e00 ' 1024 words
Const Maxwordbit = 6 'Z5 is maximum bit '
#endif
#if Loaderchip = 162 ' Mega162
$loader = $1c00 ' 1024 words
Const Maxwordbit = 6 'Z5 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
$crystal = 8000000
'$crystal = 14745600
$baud = 57600 'this loader uses serial com
'It is VERY IMPORTANT that the baud rate matches the one of the boot loader
'do not try to use buffered com as we can not use interrupts
'Dim the used variables
Dim Bstatus As Byte , Bretries As Byte , Bblock As Byte , Bblocklocal As Byte
Dim Bcsum1 As Byte , Bcsum2 As Byte , Buf(128) As Byte , Csum As Byte
Dim J As Byte , Spmcrval As Byte ' self program command byte value
Dim Z As Word 'this is the Z pointer word
Dim Vl As Byte , Vh As Byte ' these bytes are used for the data values
Dim Wrd As Byte , Page As Byte 'these vars contain the page and word address
'Mega 88 : 32 words, 128 pages
Disable Interrupts 'we do not use ints
Waitms 1000 'wait 1 sec
'We start with receiving a file. The PC must send this binary file
'some constants used in serial com
Const Nak = &H15
Const Ack = &H06
Const Can = &H18
'we use some leds as indication in this sample , you might want to remove it
Config Portb = Output
Portb = 255 'the stk200 has inverted logic for the leds
'$timeout = 1000000 'we use a timeout
$timeout = 1000000 'we use a timeout
'Do
Bstatus = Waitkey() 'wait for the loader to send a byte
Print Chr(bstatus);
If Bstatus = 123 Then 'did we received value 123 ?
Goto Loader
End If
'Loop
For J = 1 To 10 'this is a simple indication that we start the normal reset vector
Toggle Portb : Waitms 100
Next
Goto _reset 'goto the normal reset vector at address 0
'this is the loader routine. It is a Xmodem-checksum reception routine
Loader:
For J = 1 To 3 'this is a simple indication that we start the normal reset vector
Toggle Portb : Waitms 500
Next
Spmcrval = 3 : Gosub Do_spm ' erase the first page
Spmcrval = 17 : Gosub Do_spm ' re-enable page
Bretries = 10 'number of retries
Do
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
Print Chr(ack); ' send ack and ready
Portb.3 = 0 ' simple indication that we are finished and ok
Goto _reset ' start new program
Case &H18: ' PC aborts transmission
Goto _reset ' ready
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:
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
Page = Page + 1 'next page
Spmcrval = 3 : Gosub Do_spm ' erase next page
Spmcrval = 17 : Gosub Do_spm ' re-enable page
End If
Next
Toggle Portb.2 : Waitms 10 : Toggle Portb.2 'indication that we write
Return
Do_spm:
Bitwait Spmcsr.selfprgen , Reset ' check for previous SPM complete
Bitwait Eecr.eepe , 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}
Spmcsr = Spmcrval 'assign register
spm 'this is an asm instruction
nop
nop
Return
'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. And we will release a command line loader in the future