Async FIFO coregen wizard

I have tried to instantiate the Asynchronous FIFO core (v6) from 
Coregen, and it's been giving me trouble. First, I can't get it to 
produce a FIFO using distributed RAM (I wanted a 31-deep FIFO). When I 
try, it tells me there is a block RAM in the usage summary. If I try to 
open the core again after it's generated, it sometimes just beeps and 
exits (no error messages at all), sometimes it goes into the coregen 
wizard with "Block RAM" selected and the FIFO depth some enormous value 
like 65536.

I am using ISE 6.3.03i, with the latest IP core updates installed.

If it was a synch. FIFO, I have my own core, but I need an Async FIFO to 
cross clock domains and I dont want to waste a BRAM site.

-Jim

Jim-

> I have tried to instantiate the Asynchronous FIFO core (v6) from
> Coregen, and it's been giving me trouble. First, I can't get it to
> produce a FIFO using distributed RAM (I wanted a 31-deep FIFO). When I
> try, it tells me there is a block RAM in the usage summary.

We have often dealt with the same issue.  You can have distributed Ram
selected, but it still uses block ram.  Our solution has been to always
click the dist ram button before generating - even if it is already
selected.  Also always check "view core footprint" to see if it used
block ram or dist ram.  If block ram, try again.  Silly, but this issue
has been there since at least version 4, and is still there in v6.1.
Luckily you only have to get it to generate properly once...

Jason Daughenbaugh
http://www.advanced.pro