PI 4 Compute module with pci-e?

[zeilsteen]

Hello,

Fantastic you are using a soc with pci-e in the pi4. It would be even cooler if there would come a pi4 compute module with pci-e on the pins of the module.

I was even thinking of making an adapter for the usb 3.0 chip replace the chip with an adapter and m.2 socket...But that would be insane.

Or a Pi4 with m.2 slot, I think there is an extra lane free on the soc?

Cheers, goodluck and thanks !

[jamesh]

There are technical difficulties with fitting everything on a SODIMM connecter, but it's being thought about.

[zeilsteen]

Hello James,

Fantastic, and I'm in for a Pi4 M.2 edition. Or would it even be possible to change a DTS in the kernel and forward the pci-e to the header and some GPIO's?

I know i'm asking a lot here, but that would also do the trick.

Does the pi foundations do custom production design and runs or is it only Farnell doing this on it's own?

Thanks!

[Gavinmc42]

Wow, that's an idea.
Easier to make Pi4 laptop with serious storage?

Q1) What else can be down with pci-e?
It is not just memory these days that use pci-e.
That might need a different form factor, probably worth it?

[jamesh]

Wow, that's an idea.
Easier to make Pi4 laptop with serious storage?

Q1) What else can be down with pci-e?
It is not just memory these days that use pci-e.
That might need a different form factor, probably worth it?

On the Pi4 the PCIe is used to connect the USB hub, and its single channel. Not sure what else it could be used for, sure there lots of interesting things, but on the Pi4 itself, the PCIe bus is not exposed.

[Gavinmc42]

On the Pi4 the PCIe is used to connect the USB hub, and its single channel. Not sure what else it could be used for, sure there lots of interesting things, but on the Pi4 itself, the PCIe bus is not exposed.

Q1) On a Compute the pci-e would need to be exposed?
Therefore other uses for it, modems, wlan?

Q2) Do embed PC's use pci-e in instruments?

[zeilsteen]

Great I'm in on that

Looks like the alternative GPIO config is not exposing any pci-e lanes or clocks.

https://www.raspberrypi.org/documentati ... minary.pdf

Or also nice if you could add an alternative config of the DTS for the gpio and disable the usb3 or use a spare pci-e lane on the soc if it free.
Than you could use a normal pi4 and bake your own pci-e or m.2 port on the gpio.
Nice OpenWrt device in the making.

Cheers

Herman

[cdsgames]

I am also a user of compute modules for audio designs.


RPI4 is a excellent step in the right direction . You guys did great.


Please bring the CM4 to the market and expose the PCIe,

Let us use our creativity .

II would be ready to buy 1000 units to start.

www,allo.com

[aBUGSworstnightmare]

If there will be a CM4 in the future it needs to expose all the I/O which is available on the new SOC, incl. PCIe.

Don't think enough pins are available on the 200pin edge connector of the current compute modules.
Yes, I know that speculative threads will be locked sooner than later but let me raise my voice again for a Q7 form factor with MXM connector .

[thagrol]

A thought occurs: won't repurposing the PCIe lane of the Pi4's SoC mean no USB?

As I read the spec, the only USB present is connected via PCIe, the single USB port avialable on older iterations of the SoC isn't present on the Pi4.

So no device mode to flash the onboard eMMC. In fact, does the USB solution of the Pi4 even support running in device/otg mode?

You'd be stuck with using a PCIe multiplexer or USB via SPI which will likely max out at around 12Mbs "Full Speed".

[plugwash]

As I read the spec, the only USB present is connected via PCIe, the single USB port avialable on older iterations of the SoC isn't present on the Pi4.

The old USB controller is still present on the SoC. On the 4B it's connected to the USB C connector.

[thagrol]

As I read the spec, the only USB present is connected via PCIe, the single USB port avialable on older iterations of the SoC isn't present on the Pi4.

The old USB controller is still present on the SoC. On the 4B it's connected to the USB C connector.

That's good to know. Does that mean the 4B can do host and device mode at the same time?

[rpdom]

As I read the spec, the only USB present is connected via PCIe, the single USB port avialable on older iterations of the SoC isn't present on the Pi4.

The old USB controller is still present on the SoC. On the 4B it's connected to the USB C connector.

That's good to know. Does that mean the 4B can do host and device mode at the same time?

Yes. The USB-C connector is OTG and can run in host or device mode, while the main USB ports will always work in host mode only.

[Gavinmc42]

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?

[jamesh]

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.

[Gavinmc42]

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.

Longer CM4+ module for 240-288 pin connectors.
Allow for future CM5+/6+ versions, with even more room for more memory?
Is that enough room for WiFi?
You guys have nothing to do now till Pi5 arrives

History - The old ISA bus XT-AT bus expansion?

Not really serious about RPT motherboards
Time for third party people to step up.

Q1) Hey what PCB design software will run on Pi4's?

[gizmomouse]

Please bring out PCIE on CM4. I have been working on a portable handheld that has an FPGA. I have been grudgingly working with the CM3 planning on attaching the FPGA using the secondary memory interface. I'm not very happy with the throughput I will be able to achieve between the SOC and FPGA but I love the community support for the RPI.

Does this SOC support DisplayPort? If so, I would like at least two lanes in order to take advantage of USB-C alternative mode. If it was available this handheld can be an entire desktop computer by just plugging in one USB-C port using an off the shelf USB-C dongle.

[zeilsteen]

About the problem of not having enough pins on the so-dimm, I hope it is possible to build a kernel with options for pin mux.

So everyone kan use there own pins needed and choose a pinmux in raspi-config or in kernel building. . But I do not know if the soc allows this.

And you probably need some standard pins for a "mainstream" devboard to work..

Goodluck with the design if you go for the compute module 4.

Herman

[zeilsteen]

Well.

Been looking in the

bcm2711-rpi-4-b.dts
bcm2711-rpi-4-b.dts

nothing there on pci-e or usb.
But in the bcm2711.dtsi

There is :

&usb {
reg = <0x7e980000 0x10000>,
<0x7e00b200 0x200>;
interrupts = <GIC_SPI 73 IRQ_TYPE_LEVEL_HIGH>,
<GIC_SPI 40 IRQ_TYPE_LEVEL_HIGH>;
};

&gpio {
interrupts = <GIC_SPI 113 IRQ_TYPE_LEVEL_HIGH>,
<GIC_SPI 114 IRQ_TYPE_LEVEL_HIGH>;
};

Does anyone know how I can tweak this and get the pci-e lanes and clock on the gpio pins?

[W. H. Heydt]

It's interesting to see people trying to figure out what they can do with BCM2711 PCIe "lanes" (plural). You guys need to step back to reality that the SoC only has *one* *singular* PCIe lane. If you want more than one, you're going to have to wait for a future SoC and hope it has more than one lane. So don't count on those particular chickens to hatch until AT LEAST a CM5.

[incognitum]

Been looking in the

bcm2711-rpi-4-b.dts
bcm2711-rpi-4-b.dts

nothing there on pci-e or usb.

Don't think pci-e devices like the USB3 card need to be specified in device-tree, given that pci(-e) already has its own mechanism to detect cards...
So if you see a reference to usb it's more likely to be the usb-c otg port.
The pci-e controller is in bcm2838.dtsi though.

[zeilsteen]

Hello incognitum,

Thanks for pointing that out.
I really have no idea how to change the pins of the pci-e to go to the best gpio pins of the pi4. If even possible...

Would that be possible? Then we don't have to wait for a compute module with the pins on the module.
I don't need the usb 3.0 but would love the pci-e.

I have made a shield for this little friend:

https://www.friendlyarm.com/index.php?r ... uct_id=241

PCI-e works on the headers, but the pi4 would also be a nice option.

If changing the pins is possible on the pi4 it would be nice to do it to gpio's that have length matched pairs.

Herman

[jamesh]

Hello incognitum,

Thanks for pointing that out.
I really have no idea how to change the pins of the pci-e to go to the best gpio pins of the pi4. If even possible...

Would that be possible? Then we don't have to wait for a compute module with the pins on the module.
I don't need the usb 3.0 but would love the pci-e.

I have made a shield for this little friend:

https://www.friendlyarm.com/index.php?r ... uct_id=241

PCI-e works on the headers, but the pi4 would also be a nice option.

If changing the pins is possible on the pi4 it would be nice to do it to gpio's that have length matched pairs.

Herman

I do not believe it is possible to have the PCIE pins on the GPIO. No physical connection.

[John Westlake]

I suspect that due to signal integrity issues the pci-e pins cannot be shared with GPIO pins - much in the same way HDMI pins need to be separated from GPIO's.

There will need to be dedicated pins for the second HDMI and PCI-E Bus, maybe also for the Ethernet bus...

I hope that RPi make the decision to release two modules - one the CM4 (pin compatible with the current CM rage) and a CMPro with the extra highspeed interfaces.

[AYMERICRDV]

I am thinking multiple version of Computes.
CM4 and CM4+ which has the PCI-e broken out.



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.

https://www.molex.com/molex/products/da ... TACLES.xml

What if you made the board longer and had a flat board to board (B2B) connector on the far side of the SODIMM connector for the CM4 board. You would slide in the module at a 45 degree angle into the SODIMM connector and then press it into the B2B connector. That way you could use either a CM 3 or CM 4 on the same carrier board.

I know it will be tough to get a connector with the right height to match up with the B2B connector and the tolerances have to be a bit tighter. But I do think that both connectors are a bit forgiving...and the board will flex a little

Just a crazy idea....