Re: FIFO sizes

[Tom Verbeure <tom.verbeure@mie.alcatel.be>]

Meanwhile, I have been reading datasheets of some commerical chips on the
market that have similar data-rate requirements.
Eg. the Intel 82559 Fast Ethernet component has a seperate buffer of 3 K for
receive and transmit, for a data rate of 100 Mbits/s = 12 Mbytes/s, so I guess
a FIFO of 4 Kbytes should indeed be good enough.

Thanks,
Tom


Duncan Terry S Civ AFRL/DES wrote:

> Tom,
>
> We have had experiences where 4Kx16bit FIFO's were not sufficient.  Other
> bus activity blocked access for up to a msec or two.  Normally, this
> activity can be overridden by the bus master, but there can be other issues
> with that (i.e. overall system performance and you mention a heavily loaded
> system).  We are not a commercial organization and we build small numbers of
> boards (30-40) so we have started using 16Kx16bit FIFO's for robustness.
>
> One caveat is that our goal is to get throughput rates as close to 80 MB/sec
> as possible.  As this is six times faster than your desired rate, 2-4K
> FIFO's may provide the same margin for you that the 16K FIFO's provide for
> us.
>
> Terry S. Duncan
> duncant@plk.af.mil
> (505) 846-6783 voice
> (505) 853-7243 pager 7103
> (505) 846-2213 fax
>
> -----Original Message-----
> From: Tom Verbeure [mailto:tom.verbeure@mie.alcatel.be]
> Sent: Tuesday, March 14, 2000 4:43 AM
> To: pci-sig@znyx.com
> Subject: FIFO sizes
>
> Hello All,
>
> I was wondering whether there are certain rules of thumb regarding the
> sizing of transmit/receive FIFO's for master operations.
> For our current application, we will need an average transfer rate of
> roughly 15 Mbytes/s, but this can arrive in bursts. What is the maximum
> time that we should buffer our data before we will get a grant from the
> PCI arbiter? (On a heavily loaded PC)
> Assuming that this time is 100 us, a buffer of 1500 bytes should be
> sufficient. Let's take 2k byte  to have some more margin. Is this a
> reasonble size that will avoid dropped data?
>
> Thank you,
>
> Tom Verbeure
> Design Engineer
> Alcatel Microelectronics