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'[AVR]:Bootloaders and BOOTRST'
2003\11\10@232702 by Michael Milner

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Hi,

I've used PICs for quite some time and I've recently started dabbling with
AVRs (I like the gcc tool chain).

I've been trying to get a bootloader to work properly on the ATmega8.  The
bootloader code works, however I'm having trouble getting the AVR to start
in the bootloader when reset.

Supposedly programming (clearing) the BOOTRST fuse will cause the
processor to start at the beginning of the bootloader section on reset
(instead of at the application code at 0x0000).  Instead, the code starts
at the application code regardless of the value of the fuse.  Are their
any tricks to this?  Am I forgetting something?

I'm using the uisp programmer under Linux.  The following shows the
current value of the fuses:

[--START COMMAND PROMPT--]
[root@lh work]# /usr/local/bin/uisp -dlpt=0x378 -dprog=dapa --rd_fuses
Atmel AVR ATmega8 is found.

Fuse Low Byte      = 0xff
Fuse High Byte     = 0xc0
Fuse Extended Byte = 0xff
Calibration Byte   = 0xa4  --  Read Only
Lock Bits          = 0xff
   BLB12 -> 1
   BLB11 -> 1
   BLB02 -> 1
   BLB01 -> 1
     LB2 -> 1
     LB1 -> 1

[--END COMMAND PROMPT--]

Anyone have any ideas?

Thanks,

Mike

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2003\11\11@142618 by Richard.Prosser

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I've done a fair bit with the ATMega32 over the last few years (or, at
least a very similar chip).
Have used a bootloader extensively & no problems with the bootloader vector
at all.

Can you verify the fuse settings using a different programmer/reader ?

I guess other possibilities are  is that either your code is redirecting
the program flow incorrectly or that the bootloader vectors are at a
different location from where you expect them to be.

Richard P




Hi,

I've used PICs for quite some time and I've recently started dabbling with
AVRs (I like the gcc tool chain).

I've been trying to get a bootloader to work properly on the ATmega8.  The
bootloader code works, however I'm having trouble getting the AVR to start
in the bootloader when reset.

Supposedly programming (clearing) the BOOTRST fuse will cause the
processor to start at the beginning of the bootloader section on reset
(instead of at the application code at 0x0000).  Instead, the code starts
at the application code regardless of the value of the fuse.  Are their
any tricks to this?  Am I forgetting something?

I'm using the uisp programmer under Linux.  The following shows the
current value of the fuses:

[--START COMMAND PROMPT--]
[root@lh work]# /usr/local/bin/uisp -dlpt=0x378 -dprog=dapa --rd_fuses
Atmel AVR ATmega8 is found.

Fuse Low Byte      = 0xff
Fuse High Byte     = 0xc0
Fuse Extended Byte = 0xff
Calibration Byte   = 0xa4  --  Read Only
Lock Bits          = 0xff
   BLB12 -> 1
   BLB11 -> 1
   BLB02 -> 1
   BLB01 -> 1
     LB2 -> 1
     LB1 -> 1

[--END COMMAND PROMPT--]

Anyone have any ideas?

Thanks,

Mike

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