pci-x133 to parallel pci-66

[Chad Bearden]

I would like to split a pci-x133 bus into 2 parallel pci-66 busses.
Has anyone done this? I'm not afraid to purchase the Xilinx pci-x
core and halfbridge IP but just looking for some wisdom.

|--------|
| |<----- pci-66 ----->
<---pcix133--->| bridge |
| |<----- pci-66 ----->
|--------|
chad.

 

[Eric Crabill]

Hi,

Logically, what you described can be built with three
PCI-X to PCI-X bridges.

You can take bridge #1 from PCI-X 133 to PCI-X 66. On
that PCI-X 66 bus segment, you put bridge #2a and #2b,
both of which bridge from PCI-X 66 to PCI 66. So, you
can actually go buy three of these ASSPs and build
exactly what you want.

I wouldn't want to turn you away from a Xilinx solution.
A Xilinx solution could be a one-chip solution, offer
lower latency, and provide you with the opportunity to
customize your design in a way you cannot with ASSPs.
However, you would want to carefully weigh the benefits
with the downsides -- you will need to put in some design
effort. Another thing to consider is cost, which will
be a function of the size of your final design.

Good luck,
Eric

Chad Bearden wrote:

I would like to split a pci-x133 bus into 2 parallel pci-66 busses.
Has anyone done this? I'm not afraid to purchase the Xilinx pci-x
core and halfbridge IP but just looking for some wisdom.

|--------|
| |<----- pci-66 -----
---pcix133--->| bridge |
| |<----- pci-66 -----
|--------|
chad

 

[H. Peter Anvin]

Followup to: <906428f5.0310091342.3bb90eb3@posting.google.com>
By author: chadb@beardendesigns.com (Chad Bearden)
In newsgroup: comp.arch.fpga

I would like to split a pci-x133 bus into 2 parallel pci-66 busses.
Has anyone done this? I'm not afraid to purchase the Xilinx pci-x
core and halfbridge IP but just looking for some wisdom.

|--------|
| |<----- pci-66 -----
---pcix133--->| bridge |
| |<----- pci-66 -----
|--------|

If you're looking for an existing silicon solution I believe you could
do it with two Tundra Tsi310 parts.

-hpa



--
<hpa@transmeta.com> at work, <hpa@zytor.com> in private!
If you send me mail in HTML format I will assume it's spam.
"Unix gives you enough rope to shoot yourself in the foot."
Architectures needed: ia64 m68k mips64 ppc ppc64 s390 s390x sh v850 x86-64

 

[Chad Bearden]

If you mean putting both Tundra 310 bridges on a single pci-x133 bus I
don't think this is electrically supported. As I understand it you
can only have one load on pci-x133 bus. Please correct me if I have
mis-stated your intention.

chad.

If you're looking for an existing silicon solution I believe you could
do it with two Tundra Tsi310 parts.

-hpa

 

[Chad Bearden]

Eric Crabill <eric.crabill@xilinx.com> wrote in message news:<3F85E01C.A0E99EFA@xilinx.com>...

Hi,

Logically, what you described can be built with three
PCI-X to PCI-X bridges.

You can take bridge #1 from PCI-X 133 to PCI-X 66.

Aren't you cutting your bandwidth in half? I would like to have the
pci66 busses be able to run at full speed to access the host's memory
(primary side of the pcix133 bridge #1). If you drop to 66 MHz here
now my to secondary busses can only run at 1/2 there bandwidth _if_
trying to access host memory at the _same_ time.

On
that PCI-X 66 bus segment, you put bridge #2a and #2b,
both of which bridge from PCI-X 66 to PCI 66. So, you
can actually go buy three of these ASSPs and build
exactly what you want.

I wouldn't want to turn you away from a Xilinx solution.
A Xilinx solution could be a one-chip solution, offer
lower latency, and provide you with the opportunity to
customize your design in a way you cannot with ASSPs.
However, you would want to carefully weigh the benefits
with the downsides -- you will need to put in some design
effort. Another thing to consider is cost, which will
be a function of the size of your final design.

Good luck,
Eric

 

[Eric Crabill]

Hi,

Perhaps I am a bit jaded, but I think you will never
actually realize anything close to "full speed" using
PCI. (PCI-X has some improvements in protocol). Your
statement assumes that both the data source and the
data sink have an infinitely sized buffer, nobody uses
retries with delayed read requests, and you have huge
(kilobytes at a time) bursts.

Aren't you cutting your bandwidth in half?

It depends -- are you talking about "theoretical"
bandwidth, or bandwidth you are likely to achieve?

If you are designing under the assumption that you will
achieve every last byte of 533 Mbytes/sec on a PCI64/66
bus, you will have some disappointment coming.

PCI and PCI-X are not busses that provide guaranteed
bandwidth. I've seen bandwidth on a PCI 64/66 bus fall
to 40 Mbytes/sec during certain operations because the
devices on it were designed poorly (mostly for the
reasons I stated in the first paragraph).

like to have the pci66 busses be able to run at full
speed to access the host's memory (primary side of
the pcix133 bridge #1). If you drop to 66 MHz here
now my to secondary busses can only run at 1/2 there
bandwidth _if_ trying to access host memory at the
_same_ time.

While the point you raise is theoretically valid, you
must consider that the bandwidth you achieve is going to
be no greater than the weakest link in the path. What
is the actual performance of the PCI-X 133 Host? How
about your PCI 66 components? The bridge performance
may be moot.

An interesting experiment you could conduct would be
to plug your PCI 66 component into a PCI 66 host, and
see how close to "full speed" you can really get using
a PCI/PCI-X protocol analyzer.

Then, you could buy two bridge demo boards from a
bridge manufacturer (PLX/Hint comes to mind...) and
see what you get behind two bridges, configured as I
described.

I would certainly conduct this experiment as a way to
justify the design time and expense of a custom bridge
to myself or my manager. While I suspect you won't get
half of "full speed" in either case, I am very often
wrong. That's why I'm suggesting you try it out.

I'm not trying to discourage you from using a Xilinx
solution. However, I'd prefer that potential customers
make informed design decisions that result in the best
combination of price/performance/features.

Good luck,
Eric

 

[Richard Iachetta]

In article <3F85E01C.A0E99EFA@xilinx.com>, eric.crabill@xilinx.com says...

you will need to put in some design
effort.

That's an understatement!

--
Rich Iachetta
I do not speak for IBM

 

[Nicholas C. Weaver]

In article <3F86E3E4.BED89355@xilinx.com>,
Eric Crabill <eric.crabill@xilinx.com> wrote:

PCI and PCI-X are not busses that provide guaranteed
bandwidth. I've seen bandwidth on a PCI 64/66 bus fall
to 40 Mbytes/sec during certain operations because the
devices on it were designed poorly (mostly for the
reasons I stated in the first paragraph).

Also just type of transaction can contribute as well. Just TRY
streaming through (in -> memory -> out) two 1 Gb ethernet ports when
you have full rate, minimum sized packets, using PCI or PCI-X based
hardware.

I'm not trying to discourage you from using a Xilinx
solution. However, I'd prefer that potential customers
make informed design decisions that result in the best
combination of price/performance/features.

A very good attitude, I wish more companies would give such advice.
--
Nicholas C. Weaver nweaver@cs.berkeley.edu

 

[Nahum Barnea]

Richard Iachetta <iachetta@us.ibm.com> wrote in message news:<MPG.19f0c726fe699c2b98982b@ausnews.austin.ibm.com>...

In article <3F85E01C.A0E99EFA@xilinx.com>, eric.crabill@xilinx.com says...
you will need to put in some design
effort.

That's an understatement!

Hi Richard,
Can you be so kind and share some details over the effort of the
Xilinx PCI-X core solution of this problem.
I have a similiar problem - only all ports are PCI-X.

ThankX,
NAHUM.