enjoy
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Re: PI 4 Compute module with pci-e?

Sun Jul 28, 2019 7:33 pm

jamesh wrote:
Wed Jun 26, 2019 7:42 am
Gavinmc42 wrote:
Wed Jun 26, 2019 5:47 am
I am thinking multiple version of Computes.
CM4 and CM4+ which has the PCI-e broken out.

Those USB/Lan parts can be on the motherboard, two types of motherboards?
Third party MB's, 6 UART versions?

Wonder if BCM can make enough 2711's?
We don't have the staffing levels to do so many variants.

We are still thinking about how, if we were to go ahead, the CM4 would work, as as stated above, there are not enough pins on the SODIMM connector to expose everything.
CM4 would be such a great product. Have you guys thought about SMARC standard? It has 314 pins and lots of I/Os.

lost
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Re: PI 4 Compute module with pci-e?

Mon Jul 29, 2019 6:44 am

jamesh wrote:
Wed Jun 26, 2019 7:42 am
We are still thinking about how, if we were to go ahead, the CM4 would work, as as stated above, there are not enough pins on the SODIMM connector to expose everything.
+ Ethernet GMII should be there also to allow SoC controller to drive an external PHY...

If the SODIMM must be kept for compatibility, maybe another connector TDB with a PCIe line + GMII could do the job, as well as some for Wifi/BT radios.

These may be populated only on a compute module 4+ version for instance, to keep base version price range.

We see some Linux laptop (like pinebook, but OS support on ARM is usually an issue everywhere but PI...) attempts or some x86 netbook revivals (like one-mix). A compute module may now have enough horse-power to drive these kind of machines.

Some netbooks/tablets could be designed to host a PI4+ CM, being future-proof & easily upgradeable.

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Re: PI 4 Compute module with pci-e?

Mon Jul 29, 2019 5:23 pm

lost wrote:
Mon Jul 29, 2019 6:44 am
Some netbooks/tablets could be designed to host a PI4+ CM, being future-proof & easily upgradeable.
Not quite the same thing, but are you familiar with the NEC professional-grade displays that have--as an option--a CM/CM3 carrier board? NEC even brought out a 16GB variant CM3 for them. That has now been superceded by the CM3+ line.

The basic problem with a CM4 is--I think--going to be that there are more interfaces now and the there aren't enough connections on the current socket for all the new stuff. Therefore, it would make sense to have a form factor break with a CM4 (at least as far as the connector). A connector should be chosen that has a reasonable number of possible connections in excess of what the CM4 actually needs to allow for any new interfaces that might show up in the future...at least for 2 or 3 generations out, and the longer the better.

mc_hof
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Re: PI 4 Compute module with pci-e?

Wed Jul 31, 2019 1:07 pm

enjoy wrote:
Sun Jul 28, 2019 7:33 pm
jamesh wrote:
Wed Jun 26, 2019 7:42 am
Gavinmc42 wrote:
Wed Jun 26, 2019 5:47 am
I am thinking multiple version of Computes.
CM4 and CM4+ which has the PCI-e broken out.

Those USB/Lan parts can be on the motherboard, two types of motherboards?
Third party MB's, 6 UART versions?

Wonder if BCM can make enough 2711's?
We don't have the staffing levels to do so many variants.

We are still thinking about how, if we were to go ahead, the CM4 would work, as as stated above, there are not enough pins on the SODIMM connector to expose everything.
CM4 would be such a great product. Have you guys thought about SMARC standard? It has 314 pins and lots of I/Os.
SMARC is too big in many applications and migration of products from CM3 (SODIMM200) to SMARC would be impossible. Therefore I would propose instead to migrate to 260 contact SODIMM socket like https://www.te.com/usa-en/product-2309413-1.html . This way you could have all interfaces broken out and fit it mechanically in the same space as the CM3. Of course, the downside is you will have to re-route the base PCB, but you have to do that for the SMARC case as well.
But if you change the pin-out intelligently, so that the legacy signals remain more or less at the same mechanical position on the SODIMM, the effort for re-routing could be minimized to a matter of hours. You could add a pair of contacts every 6 ... 7 contact pairs. At one position you would have to add two pairs (for PCIe).
If it were my choice, this is how I would do it. I agree that there should by a backward compatible CM4 variant in SODIMM200 form factor, without PCIe.

To sum up, my proposal would be:
- CM4 in SODIMM200, backward compatible to CM3(+)
- CM4 Lite in SODIMM200, backward compatible to CM3(+) Lite
- CM4-260 in SODIMM260, with PCIe and other additional interfaces broken out to the SODIMM260, eMMC on module
- CM4-260 Lite in SODIMM260, with PCIe and other additional interfaces broken out to the SODIMM260, eMMC off module

We have an industrial application in mind and need PCIe as a fast and low-latency data link to a FPGA. I would really like to see that CM4 sticks to the principles of CM3: Means, only have the minimal set of components on the module, that keeps the module low-cost and highly flexible at the same time. Functions like USB3 controller or Ethernet PHY don't belong on the module but on the base board.

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Gavinmc42
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Re: PI 4 Compute module with pci-e?

Thu Aug 01, 2019 5:59 am

- CM4 in SODIMM200, backward compatible to CM3(+)
- CM4 Lite in SODIMM200, backward compatible to CM3(+) Lite
- CM4-260 in SODIMM260, with PCIe and other additional interfaces broken out to the SODIMM260, eMMC on module
- CM4-260 Lite in SODIMM260, with PCIe and other additional interfaces broken out to the SODIMM260, eMMC off module
Yep, something like that.
The BCM27111 is so much better, that PCI-e :D
Let the users figure out the thermals ;)

Wonder how well the CM4 will go with dual cameras?
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jamesh
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Re: PI 4 Compute module with pci-e?

Thu Aug 01, 2019 8:53 am

Gavinmc42 wrote:
Thu Aug 01, 2019 5:59 am
Wonder how well the CM4 will go with dual cameras?
Same as CM3. Camera silicon is the same.
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Re: PI 4 Compute module with pci-e?

Wed Aug 07, 2019 11:55 am

Jamesh, how can you estimate the possibility of realizing two these options in CM4 line, suggested by @mc_hof:
- CM4 in SODIMM200, backward compatible to CM3(+)
- CM4 Lite in SODIMM200, backward compatible to CM3(+) Lite
Just a curious... :geek:

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Re: PI 4 Compute module with pci-e?

Wed Aug 07, 2019 1:42 pm

I'm afraid I cannot give out any details of future product.
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Re: PI 4 Compute module with pci-e?

Wed Aug 07, 2019 7:43 pm

jamesh wrote:
Wed Aug 07, 2019 1:42 pm
I'm afraid I cannot give out any details of future product.
Ok, got it. I keep calm and wait. :-)

toshas
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Re: PI 4 Compute module with pci-e?

Mon Aug 19, 2019 7:10 pm

IMHO PCI-E is definitely a "must have" feature for CM4.
One lane can be muxed on base board up to 3/4 devices via costless Diodes/Pericom 1-to-3/4 PCIe Switches.
So we will have network, nvme storage and so on.

Usually x1 pcie requires 3 differential pair (rx/tx data and ref. clock).
Synchronous clocking scheme has wider/better support than asynchronous scheme.
These pins can't be switched with others because it is not general purpose IO, but high-speed transceivers.

+1 for AYMERICRDV idea.
It can be done also via additional FPC connector and short cable.
Like these guys did it - http://eshop.sintech.cn/pcie-x1ub-to-mi ... -1005.html
Of course additional effort for signal integrity check is required.

260 pin SODIMM (as mc_hof said) is much more robust solution.
Here "what is on top ?" should be discussed. Compatibility or future perspectives.
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Mikeynl
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Re: PI 4 Compute module with pci-e?

Thu Aug 22, 2019 9:46 am

My biggest concern despite the pci-e is the backward compatibility. Whatever happens and created, should be backward compatible :)!!

aBUGSworstnightmare
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Re: PI 4 Compute module with pci-e?

Thu Aug 22, 2019 11:50 am

Mikeynl wrote:
Thu Aug 22, 2019 9:46 am
My biggest concern despite the pci-e is the backward compatibility. Whatever happens and created, should be backward compatible :)!!
backward compatibility at the sake of loosing new features makes no sense ..
So for exiting stuff one can keep using CM3/CM3+ and for new stuff they can use CM4 (if it becomes reality)

Mikeynl
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Re: PI 4 Compute module with pci-e?

Fri Aug 23, 2019 9:23 am

aBUGSworstnightmare wrote:
Thu Aug 22, 2019 11:50 am
Mikeynl wrote:
Thu Aug 22, 2019 9:46 am
My biggest concern despite the pci-e is the backward compatibility. Whatever happens and created, should be backward compatible :)!!
backward compatibility at the sake of losing new features makes no sense ..
So for exiting stuff one can keep using CM3/CM3+ and for new stuff, they can use CM4 (if it becomes reality)
We can do a yes / no game. For us means backward compatibility a very important aspect in the lifecycle of our products. And I bet with me a lot others will preach the same. Backward compatibility means that lifespan of many products will expand. Good for our environment :)!

//edit i can live with a daughterboard that go from 240 pins back to 200. We have space for that.

Whiterat
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Re: PI 4 Compute module with pci-e?

Fri Sep 06, 2019 9:57 pm

I was going to say what about using a couple of low profile mezzanine / board-to-board connectors and then provide a SODIMM200 shim for backwards compatibility..but then I'm forgetting how cheap SODIMM carriers are which is half the point.

The backwards compatibility is important and I appreciate the reason the foundation wishes to keep it - as well as those who've invested in custom carriers (potentially either at great cost , great quantity - or both) however as others have said, it would be a real shame to limit a potential CM4 for the sake of this backwards compatibility.

However, ff there isn't room to expose PCIE over the SODIMM200 connector then the only *real* gains would be CPU and USB3 OTG - which then begs the question, does that alone warrant a new CM?

I'm of the opinion that CM4 (and subsequent) should ditch SODIMM200 and go with SODIMM260 (or another cost effective high pin count solution).

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Re: PI 4 Compute module with pci-e?

Fri Sep 06, 2019 11:41 pm

Whiterat wrote:
Fri Sep 06, 2019 9:57 pm
However, ff there isn't room to expose PCIE over the SODIMM200 connector then the only *real* gains would be CPU and USB3 OTG - which then begs the question, does that alone warrant a new CM?
The OTG port on the Pi4B is the "legacy" USB 2.0 port.

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thagrol
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Re: PI 4 Compute module with pci-e?

Sat Sep 07, 2019 10:40 am

Whiterat wrote:
Fri Sep 06, 2019 9:57 pm
However, ff there isn't room to expose PCIE over the SODIMM200 connector then the only *real* gains would be CPU and USB3 OTG - which then begs the question, does that alone warrant a new CM?
Let's not forget more RAM.
This space unintentionally left blank.

mc_hof
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Re: PI 4 Compute module with pci-e?

Tue Sep 10, 2019 12:06 am

thagrol wrote:
Sat Sep 07, 2019 10:40 am
Whiterat wrote:
Fri Sep 06, 2019 9:57 pm
However, ff there isn't room to expose PCIE over the SODIMM200 connector then the only *real* gains would be CPU and USB3 OTG - which then begs the question, does that alone warrant a new CM?
Let's not forget more RAM.
And also let's not forget the additional serial interfaces like more I2C, SPI and so on which are extremely handy in industrial applications. But above all other enhancements, the PCIe interface with its universality, high speed and low latency would give the CM4 a real boost since it opens doors to many applications which could not be realized otherwise.

There are many more use-cases for the PCIe interface besides the USB3.x bridge. USB3 might be useful for the standard RPi4, but not so in industrial applications with CM4 because of the inherently high latency of USB. If for example you wanted to connect an FPGA to a CM4, and if this FPGA contains no CPU but just logic, then the only choice for a low-latency link would be PCIe. Ok, also SPI is low-latency, but data throughput of SPI is lower by several orders of magnitude. So if your FPGA contains logic that needs to exchange data with the CM4 with low-lateny AND high-speed at the same time, PCIe really is your only choice.

Now, if you accept that PCIe is a very versatile and useful interface and if you think about signal integrity of PCIe data links, the SODIMM260 connector is a solution that is safe and low-cost at the same time. I therefore would like to repeat my proposal from an earlier post:
- CM4 in SODIMM200, backward compatible to CM3(+)
- CM4 Lite in SODIMM200, backward compatible to CM3(+) Lite
- CM4-260 in SODIMM260, with PCIe and other additional interfaces broken out to the SODIMM260, eMMC on module
- CM4-260 Lite in SODIMM260, with PCIe and other additional interfaces broken out to the SODIMM260, eMMC off module

mc_hof
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Re: PI 4 Compute module with pci-e?

Tue Sep 10, 2019 12:39 am

One more thing: I know, this topic is about PCIe, but since we also discussed about connectors, let me add:
Another reason for a CM4 in SODIMM260 form factor ist the RGMII interface. Most people don't want the Ethernet PHY on the CM4 module because of the following reasons:
  • the PHY consumes too much PCB space
  • the PHY consumes too much power
  • the PHY on the module would make it more expensive
  • in many industrial applications you rather want to hookup up an ethernet switch or a different type of PHY
  • in cases where you don't need ethernet at all, you maybe want to use the RGMII IO pins for another purpose.
So you need another dozen pins or so for RGMII on the connector.

We need PCIe
We need RGMII
-> We need CM4 in SODIMM260

180lifer
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Re: PI 4 Compute module with pci-e?

Tue Sep 10, 2019 12:56 am

Maybe the next Pi (5?) will have a different form factor and more PCIe lanes. I’m not asking for official comment on this because we know the answer :)

But, I think it’s clear both from the comments here and from the tinkering others are doing to expose the PCIe of the Pi 4 that interest is high, both consumer and industrial/commercial in additional functionality. And while official statements are rare we do know for sure they read the comments.

It is my hope that the next Pi will be a true game changer, throwing backwards compatibility out the window and setting a new standard.

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Gavinmc42
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Re: PI 4 Compute module with pci-e?

Tue Sep 10, 2019 6:20 am

Found this, I was looking for Pi4 buildroot
http://mloduchowski.com/en/blog/raspber ... i-express/
For those who want to try PCI-e before a CM with PCI-e shows up?
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MikeDB
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Re: PI 4 Compute module with pci-e?

Wed Sep 18, 2019 7:05 pm

Lots of good ideas here which hopefully will be read. My thought is that if you expose PCIe, don't some of the other pins become less relevant and things that could be relocated off the board for provision by other PCBs, thereby reducing the pin count ?

Alternatively if you are going to use more pins, give a thought to putting two SoCs on the CM4. One could drive the PCIe whilst the other could deal with USB, etc. Cost is higher but the performance per cm^3 would open up numerous opportunities in applications where a small form factor motherboard with Intel processor is the only current option. Link the two through the camera or some other pins, whatever is fastest without removing useful functionality.

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