I think I've found it; it is about watchdog behaviour after reset (watchdog is used to restart microcontroller with "restart" uart command). It is mentioned in avr-libc documentation:
Quote:
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Note that for newer devices (ATmega88 and newer, effectively any AVR that has the option to also generate interrupts), the watchdog timer remains active even after a system reset (except a power-on condition), using the fastest prescaler value (approximately 15 ms). It is therefore required to turn off the watchdog early during program startup
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So after "software reset", either by direct command or firmware upgrade process watchdog timer is left at 15 ms until power-off because there's no wdt_disable nor wdt_reset in bootloader code.
This is where I need your help - I tried to add few lines for disabling wdt, but I can't successfully compile into working hex. I can't do it even with unchanged code; here's how I try it:
- installed latest (20100110) WinAVR on Win XP laptop
- copied bootload.c, misc.asm, autocrc.h, genautocrc and Makefile into C:\000
- run "make"
- joined output file bootload.hex with couc-crc-16k.hex (yes, i know how to join hex files in Notepad)
- checked fuses and uploaded joint hex into processor
...and nothing - while it should start blinking led
Do you have any suggestions how to debug this thingy? I think I'll start with switching led in bootloader code to see where it's stuck. Any better ideas?