ABB IRB 6400 retrofitting

Ok I can confirm that linuxcnc seems working correctly, no whatchdog bites, ~100us for servo-thread, ~20us for hostmot2 write and ~100us for hostmot2 read and no hm2_eth packets error.
There's no error also with manual loading all components.
The only problem is that the 7i94 is not responding, afterall the leds light up and the board is not responsive...
What can be the problem? I can't figure it out...

What do you mean that the card is not responsive?

I would expect all green user LEDs to illuminate
(since they are counting up too fast to follow)

But if I have the pin hm2_7i94.0.led.CR01 that with Dir=IN and I set it to false, nothing happens. So is the right behavior to not have control of the user leds even if there are the pins available?

Then the other problem is that I don't have any sserial entry in hal configuration.

Yes the hostmot2 LED register is accessible but the default
7I94 LED EEPROM setting is to show RX packet count

If you don't have any sserial entries, it means the sserial hardware
was not detected (most likely wiring or remote setup issues)

Thankyou for the info! So now I've been able to connect the stmbl to one motor resolver with success!

Still I can't connect the stmbl to the 7i94 with the sserial. I added to the end of the stmbl config the "link sserial", the leds on the cmd port of the stmbl lights up, but still any "stmbl" or "sserial" entry in the "hal config".

I also checked the ethernet cable for the sserial and has all cables without cable crossing... is it right?

Yes, a Straight through cable is used (at least for all Mesa SSerial remote cards)

Ok but looking to the pinouts in the documentations seems that the polarities are swapped. If that's the case I need to make a custom cable.
Could be the case?

I doubt it, Probably just a different interpretation of + and -.
Mesa uses the EIA RS-422/423/232 interoperability spec
which means XX+ is the inverted signal

There are 2 wiring standards for ethernet. 568a and 568b. The example Mesa provide is for 568b
Sounds like your cable (like mine) is 568a. Check your wiring standard and modify the example to suit your card.
It really would be nice if Mesa added wiring diagrams for 568a as well.