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PCI Express on the Raspberry Pi 4

mloduchowski.com

41–50 of 166 posts

Re: PCI Express on the Raspberry Pi 4

#41
post #37

Earlier quoted context omitted.

I use tmux and vim over ssh. You mean Arch? Yeah why not. Then also a lot webpack, Docker: wondering if they would get the Pi stuttering when compiling/building? And if vim is still smooth then (which isn't the case with my 20$ vps).

AArch64 is what the 64-bit version of the ARM instruction set is called.

ah right, think all software I use are available as AArch64 binaries.

Re: PCI Express on the Raspberry Pi 4

#42
post #3

Hmm, how about using this for fast interconnect for making rpi clusters?

Wouldn't the gigabit LAN be a better fit for this? If you want to make a cluster, you need to make some custom hardware to connect to, that can facilitate the communication. At this point you're likely spending more that if you just bought a real desktop for more performance. I can see the fun factor in hacking the system together, though.

> Wouldn't the gigabit LAN be a better fit for this?

I might be showing my age but...

Imagine a Beowulf cluster of these!

(For those who don't know the reference, this used to be a common saying in slashdot back in the day.)

Re: PCI Express on the Raspberry Pi 4

#43

Why not, but I will wait for a classic ATX ARM motherboard instead. It should happen this year.

Is Mini-ITX for $550 acceptable? https://www.solid-run.com/nxp-lx2160a-family/honeycomb-works...

16 core A72 CPU, up to 64GB RAM, PICe x8, 10GbE SFP+ ports and 1GbE RJ45, SATA.

It's early access hardware, so it may have some pain points. Normal units will be available from the end of the year for $750.

If I would have time and money right now, that's what I would buy.

Re: PCI Express on the Raspberry Pi 4

#45

It looks like an unreliable modification. Running a GHz-level interface with jumpers is almost impossible to control the impedance, it's a cool Proof-of-Concept though. But is it possible to bring the project to the next level? Is it possible to make a daughterboard with QFN connector? If so, one can make a pin-compatible daughterboard with an extension connector. To use it, just desolder the USB chip and solder a ne…

36 gauge wire, and twisting them into pairs would help, or parallel and flat against the PCB.

Re: PCI Express on the Raspberry Pi 4

#46
Wow, that was quick. Given that this is Broadcom, I don't suppose there is any visibility into the Root Complex? When troubleshooting PCIe it'd be nice to have the LTSSM state at least. Would be really cool to get eye diagrams...

Re: PCI Express on the Raspberry Pi 4

#47
post #9

Earlier quoted context omitted.

Wouldn't the gigabit LAN be a better fit for this? If you want to make a cluster, you need to make some custom hardware to connect to, that can facilitate the communication. At this point you're likely spending more that if you just bought a real desktop for more performance. I can see the fun factor in hacking the system together, though.

There are two ways of doing clusters - one is a message passing paradigm, which you can do over Ethernet (to an extent - I’d still take USB3 for 4x the bandwidth) - and the other is direct memory access a’la Cray. What really motivated me to do this hack is the relative abundance of stuff I can now plug into an FPGA :)

So your plan is to attach an FPGA to the PCIe bus? To allow the FPGA to access peripherals on the Pi side or do you want the FPGA to make the pi a lot more powerful?

Re: PCI Express on the Raspberry Pi 4

#48
post #42

Earlier quoted context omitted.

Wouldn't the gigabit LAN be a better fit for this? If you want to make a cluster, you need to make some custom hardware to connect to, that can facilitate the communication. At this point you're likely spending more that if you just bought a real desktop for more performance. I can see the fun factor in hacking the system together, though.

> Wouldn't the gigabit LAN be a better fit for this? I might be showing my age but... Imagine a Beowulf cluster of these! (For those who don't know the reference, this used to be a common saying in slashdot back in the day.)

+5 Funny

Re: PCI Express on the Raspberry Pi 4

#49
post #44
post #3

Hmm, how about using this for fast interconnect for making rpi clusters?

You'll lose fast storage. So you end up with devices with 40MB/s uSD cards and multi-gigabit interconnect.

Well, with the 4GB, and rumoured 8GB, you can just load everything to RAM on boot and not worry about storage at all.

Re: PCI Express on the Raspberry Pi 4

#50
post #30

It looks like an unreliable modification. Running a GHz-level interface with jumpers is almost impossible to control the impedance, it's a cool Proof-of-Concept though. But is it possible to bring the project to the next level? Is it possible to make a daughterboard with QFN connector? If so, one can make a pin-compatible daughterboard with an extension connector. To use it, just desolder the USB chip and solder a ne…

It looks like an unreliable modification. PCIe is surprisingly robust at short lengths. For example, [NanoPi_M4] has two lanes of PCIe coming to the daughterboards via old-school 0.1" connector. Something that many electrical engineers would cringe at, and yet - it works rather reliably. [NanoPi_M4] http://wiki.friendlyarm.com/wiki/index.php/NanoPi_M4#Layout

Exactly, the PCIe reference clock is "only" 100MHz.

USB 2.0 runs at 480MHz and motherboards have used 0.1" headers for them since the beginning.

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