Need help with debugging HPS

I don't like to answer to my own post, but after struggling one more day with the hardware and digging in the forum I eventually found a way to solve the problem.

I'm still not 100% sure everything is ok, but at least I can now run my baremetal application, blink the LEDs and read button status.

I write here FYI the main points which fixed the problem; I hope this could help someone else.

1.

Until this morning I tried to operate the DE0-Nano with the supplied SD card or with no card inserted at all: I was persuaded the latter should be the correct configuration.

Then I found this thread (https://www.alteraforum.com/forum/showthread.php?t=56558) which suggested there could be is a hps boot problem when no SD card is connected; on the other hand the boot provided by the original SD card image (with Linux OS or whatever) brings the hps in a state not compatible with a baremetal application (I guess it activates a watchdog or any other OS specific feature)

So I removed the supplied SD card and replaced with a blank one. Now the system is stable and I can load my application without errors.

2.

The baremetal reference code I'm using includes "alt_printf.h" among the other hwlib related header files.

I didn't investigate the reason, but including this .h file prevents the debug printf output to show on the app console panel.