Forum: µC & Digital Electronics AVR32 uc3c startup troubleshooting

Author: hBechtold (Guest)
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I'm working on a board as follows: own design with at32uc3c2256, 
Ethernet PHY TI/National DP83484I, 3.3 Volt supply local from DC/DC 
converter, a few gpio pins, PWM, TWI, no use of ADC/DAC, but analog 
power supply connected to 3.3 V and bypassed, as recommended. The master 
clock is external osc. 25 MHz, obtained by dividing the 50 MHz PHY clock 
by two.
The software uses FreeRTOS and the lwip stack from AVR Studio 6  ASF 

We build five prototype boards, six layer pcb according to Atmel and TI 
design recommendations. After fixing some minor hardware and software 
bugs, two of the five boards work pretty well, including Ethernet 
operation, after flashing and starting via JTAG, as well as powered up 
stand allone.

But the boards no. 3 to 5 show a strange behaviour: They work perfectly, 
including ethernet, if flashed and started via the JTAGICE3 debugger by 
means of the AVR studio. After booting the target, I even can quit the 
debugger, pull the JTAG connector off and the board continues to run. 
But if I start the board without JTAG, the CPU seems not to run at all. 
The PHY works, lights its 'link' LED when connecting the Ethernet cable, 
even the 'activity' LED flashes if I try a ping to the target's address. 
But the CPU seems not to execute a single line of code. I placed a 
couple of bit toggles onto some unused gpio pins, they work perfecty 
when starting the target via the studio, but I can't measure a single 
edge there if the target was powered up stand allone.

All voltages and (external) clocks are ok, the same as when the board 

The debugger doesn't help much, because the system runs pretty well when 
JTAG connected and started by the studio. If I press the reset button 
after quitting the debug session in the studio, while still having JTAG 
connected, the target resets, but does not start again, so the pure 
electric connection to the JTAGICE3 seems not to play a role.

Any ideas about troubleshooting strategies?
How can I reset the target without flashing and without the 
unconditional stop in the first line of 'main.c'?


Author: hBechtold (Guest)
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Hello again,

it's always the simple things which cause the worst headaches!

I found it by myself, here for all the others, trapping into the same 

After a hardware reset, the hardware watchdog may be enabled, depending 
on the fuse settings. In the software, the first thing we coded, was to 
disable the watchdog by calling the ASF driver function "wdt_disable()", 
which resets the enable bit in the AVR32_WDT control register. But this 
function has never been called because the watchdog time setting was far 
too short for reaching that function call.

When flashing these chips the first time, don't forget to disable the 
watchdog in the WDTDISRV fuse bit first, otherwise the processor may run 
into an infinite loop by permanently resetting itself.

The JTAG debugger broke this loop by intervening via hardware and when 
starting the user code at main(), the driver function was called at 
first, seemingly solving the problem, so that it was impossible to find 
the bug by means of the debugger only.


Author: Bruno Kempf (b0bbyr4y)
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Hi hBechtold,

thanks for telling us your solution. We had the same Problem!


Author: Alen (Guest)
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Hi Horst

You just saved me hours (maybe days) of struggle, as first google result 
was your post.

Just so you know - there is one person on planet who'll be always 
grateful for this post.

All the best


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