Fix the Buffer Empty interrupt, for the V0 release

[rodmarfran]

Isuue:

• The Buffer Empty interrupt is not working properly, but it was difficulty to isolate the problem since we did not have a working machine;
• With the complete channel working properly in direct loop, it became possible (and necessary) to verify if the Buffer Empty Interrupt really is not working and why;
• This Interrupt is crucial for the correct work of multiple channels.

[rodmarfran]

@Tiagoeem needs to adapt the SW to work with the interrupt, so @ericolucasm can test it and verify if this interrupt is, indeed, not working. Modifying the HW before that could cause more bugs than correct.

Best case scenario, this interrupt is already fully functional.