It's never to late !!!

Some modifications were done on the SLINK64 protocol. Normally they don't affect the FED developer, but they should be know in case of .......

1. The original specification mentions that when LFF (Backpressure) is activated (LOW), the FED is able to send only 2 words , others will be lost.

     In the actual SLINK card (CMS) , when the LFF (backpressure) is activated, FED can write up to 32 more word.

2. UTEST signal on the SLINK64 connector.

    In the SLINK card, this pin is not  used (reserved). A test link is activated only from the DAQ side (FRL board request the test link). During the Test link the pin LDOWN is LOW to indicate to the FED that it's no allow to send data ( LFF, Backpressure signal , will be also LOW)

3. The LDOWN signal :

 The LDOWN becomes active (=low) in one of the following conditions:

1) The FRL sets LDOWN active via a control command.
2) The SLINK cable is unplugged.
3) The FRL is performing a link self-test.
4) The FED is issuing a URESET (URESET should be active for 32 FED clock cycles to be taken in account).

>From this it follows that the LDOWN is inactive only if ALL of the
following conditions are met:

1) The FRL does NOT perform a link self test and
2) The cable is plugged in on both sides and
3) The FRL does NOT actively drive the LDOWN low.
4) The FED is NOT issuing a URESET.

Currently the FRL is operated that the LDOWN is only released at
the start of a run. This means the FED must not rely on the fact
that LDOWN goes high in order to finish any FED-initialization
procedure.
In particular the FED must not wait for LDOWN going high after issuing
URESET before URESET is released. If URESET is issued it should be
applied a fixed number of clock cycles (e.g 5) after which the FED
should release it.

It is recommended that the FED does not operate at all the URESET (A power_on reset or user reset can be issued without condition).
The entire SLINK sender is reset from the FRL before a run starts.