[Libre-soc-dev] AON21 : the solution to the set/reset flip-flop

[whygee at f-cpu.org]

Hello,

Some months ago (?) I read that there "needed" to be a new gate design
to implement the set-reset latches for the scheduler/scoreboard.
I have not seen any follow-up but it just strikes me now :

http://www.vlsitechnology.org/html/cells/wsclib013/aon21.html
This is available under Alliance and others.

Just loop the Z output to the A2 input and you're done.
SET is the B input and A1 is a (negative) reset input.
SET has priority, you can change this by using
http://www.vlsitechnology.org/html/cells/wsclib013/oan21.html
or even better :
http://www.vlsitechnology.org/html/cells/wsclib013/oan21b.html
(smaller and with positive RESET)

If you want to have extra optimisation points, you could
loop with a poly wire (to save some metal routing) and remove
the looped A input from the gate description to prevent error messages.

No idea if this helps right now but it's good to know :-)

yg