Hello,
I'd like to debug on an AT90CAN32 target on a bread board assembly.
My cheap chinese jtag did not accept this.
The avarice manpage says
at90can32 (o)
o - Only supported by the JTAG ICE mkII and AVR Dragon device.
So I purchased one of the famous dragon boards.
But still debug does not work.
I can connect, read, flash, fuse with avrdude and at least connect and
flash with avarice.
But when it goes to debug, it takes alread quite long (~ 20 sec) for
avr-gdb to come up. Dragon's LED keep flashing during most of start
up time.
When I try to run my code, it stucks in an endless loop:
======8<==================================
(gdb) ni
0x00000000 in __vectors ()
3: x/i $pc
=> 0x0 <__vectors>: rjmp .-2 ; 0x0 <__vectors>
2: /t $SREG = 0
1: /x *$PORTD = 0x4
(gdb) ni
0x00000000 in __vectors ()
3: x/i $pc
....
======8<==================================
Anything else than ni single stepping lets hang both avr-gdb and
avarice.
avr-gdb does not accept ctrl-C any more (at least not within reasonable
time).
Dragon LED's keep blinking at ~~ 2 Hz.
Looks like the endless loop is processed tremendously slow and stuff is
accumulated in some large buffer.
I can stop avarice with ctrl-C and avr-gdb dies with it.
I have to reset OCDEN fuse manually, if I want to run code on the device
after that.
But I assume that's a symptom related to the forceful break, not related
to the root cause.
When I compare the code from my elf file, I see different code at 0x000
than a rjmp .-2
======8<==================================
:~/test/AVR/hello/timer$ avr-objdump -d timer.elf
timer.elf: file format elf32-avr
Disassembly of section .text:
00000000 <__vectors>:
0: 0c 94 4a 00 jmp 0x94 ; 0x94 <__ctors_end>
4: 0c 94 54 00 jmp 0xa8 ; 0xa8 <__bad_interrupt>
8: 0c 94 54 00 jmp 0xa8 ; 0xa8 <__bad_interrupt>
c: 0c 94 54 00 jmp 0xa8 ; 0xa8 <__bad_interrupt>
.....
======8<==================================
So from a beginners educated guess, the debugging machine seems to
write this endless loop code at the device start address but does not
complete other steps to setup successful debugging???
The behaviour is the same with avarice 2.11 shipped with debian jessie
and with avarice 2.13 built from sourceforge sources.
For a refernce point, I tried the dragon setup on an Atmega32 target
attached to a simple pollin board.
It still displays the slow setup and the slow single steps. But after
the first ni command, I get assembler and source code displayed in my
gdb as configured and the code is executed in normal sequence.
I also have the sticky OCDEN fuse after (regular) shutdown.
Compared to my first experience, a cheap 7€ chinese dongle on the same
target debugs at least 10 times faster than the genuine part.
Google led me to
http://www.avrfreaks.net/comment/241039#comment-241039
"I think there's no debugging option except for the JTAGICE mkII for
those units..."
But this statement conflicts the avarice man page compatibility list.
Have I been trapped by some AVR marketing "feature"?
"Thou shalt not use cheap stuff where AVR does not make money from"?
Is it a silly beginners error?
Can it be an electric / EMC issue on my bread board assembly?
Or have I encountered a real bug?
Any help or hints are appreciated :-)
--
Wolfgang Rosner
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