Resetting FIFO

[ALuPin]

Hi,
maybe someone can give her/his opinion concerning the following question:
Thank you in advance.


I have a FIFO template with one write clock and one read clock. These
clocks are full asynchronous to each other.

Apart from that I have an asynchronous reset port in the FIFO.

My question:

Let us assume that I sychronize the asynchronous reset coming from FPGA
input pin
in a flip flop chain to synchronize it to the write clock

and in a second flip flop chain to synchronize it to the read clock.

Which synchronized reset do I have to use
to reset the FIFO in a safe manner ?

Rgds
André

 

[Gabor]

Hi,
maybe someone can give her/his opinion concerning the following question:
Thank you in advance.


I have a FIFO template with one write clock and one read clock. These
clocks are full asynchronous to each other.

Apart from that I have an asynchronous reset port in the FIFO.

My question:

Let us assume that I sychronize the asynchronous reset coming from FPGA
input pin
in a flip flop chain to synchronize it to the write clock

and in a second flip flop chain to synchronize it to the read clock.

Which synchronized reset do I have to use
to reset the FIFO in a safe manner ?

Really the FIFO design needs to handle synchronizing the single
async input to both clocks internally. I would suggest synchronizing
to the write clock and then making sure your write logic stays
quiescent (doesn't start writing) for a few cycles after reset in
case the FIFO hasn't finished resetting the read state logic. In
the Xilinx COREgen designs, reset asserts both FULL and EMPTY, which
effectively prevents reads or writes during the reset condition
and until each of these signals de-asserts synchronously to its
respective clock.