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PCI Express on the Raspberry Pi 4

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Re: PCI Express on the Raspberry Pi 4

#121

Post by notaplumber »

qdot_me wrote: post #6
Jonnax wrote: post #2

That's really cool. I'm curious, would it be possible to use a modern GPU (running at 1x) on an ARM based board? Would the open source drivers that are part of the Kernel work out the box on ARM?

Hack’s creator here - it’s on my list of things to try. GPUs are notoriously hard to get to work on non-intel, having tried to get a few up on Alpha and Itaniums in the past. VideoBIOS expects to run and expects a well behaving Intel CPU to do the power-up. That said X can sometimes emulate these quite well. On ARM we’d also run into alignment issues and likely other quirks - but in principle...

OpenBSD has radeondrm enabled on mips64, powerpc and arm64. It can initialize the board just fine without emulating x86, since KMS. Working 3D acceleration is another story.

OpenBSD even has (or had, build breaks often) packages for chromium browser on arm64 that were tested on this.

Re: PCI Express on the Raspberry Pi 4

#122

Post by kingosticks »

theonlyklas wrote: post #106
Millennium wrote: post #101

If a Pi is capable of this already, why not replace the Ethernet, charging, micro-HDMI, and USB ports with a boatload of type-C Thunderbolt ports (plus support for the HDMI 1.4 alt mode)? Would 8xUSB-C cost that much more than 1xUSB-C+1xEthernet+2xMicro-HDMI+2xUSB3+2xUSB2 (with no PCI Express), in exchange for a considerably more flexible device?

Considering the fact that 1 USB C Thunderbolt port can power a dock that could do multiple HDMI, Ethernet, USB, VGA, etc, I agree completely and I hope that they release a Raspberry Pi4C.

Remember the 1xUSB-C they have is power only, adding a proper USB-C port is something else entirely.

Re: PCI Express on the Raspberry Pi 4

#124

Post by quenstionsasked »

monocasa wrote: post #85
segfaultbuserr wrote: post #5

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…

I've seen pcie literally run over a metal clothes hanger soldered to the board. It's extremely tolerant of terrible quality connections.

Where do you work?

Re: PCI Express on the Raspberry Pi 4

#126

Post by vardump »

beatgammit wrote: post #98
buildbuildbuild wrote: post #72

Fun. If you want PCIe on a SBC without the soldering, I highly recommend perusing Hackerboards. I'm very happy with my RockPi 4 (4GB RAM, PCIe, USB 3, 6 cores), which I discovered through their excellent database. https://www.hackerboards.com/search_boarddb.php

I think you mean the RockPro64. The Rock64 only has 4 cores and no PCIe. That being said, I missed the PCIe on the specs last time I was comparing SOCs and I had forgotten about hackerboards, thanks for the reminder!

RockPro64 also has 4x low power A53 cores up to 1.5 GHz and 2x A72 cores up to 2.0 GHz. Big-little style. Just for the curious, so don't need to look it up.

SoC: http://rockchip.wikidot.com/rk3399

Re: PCI Express on the Raspberry Pi 4

#127

Post by Scuds »

_ea1k wrote: post #117
beatgammit wrote: post #98

Earlier quoted context omitted.

I think you mean the RockPro64. The Rock64 only has 4 cores and no PCIe. That being said, I missed the PCIe on the specs last time I was comparing SOCs and I had forgotten about hackerboards, thanks for the reminder!

Amusingly, there appears to be no relationship between the "Rock Pi" and the Rock64/RockPro64 family. These names are really confusing.

They're both based on a Rockchip SOC and any copyrights around "Pi" and "Rock" or "Orange Pi" don't seem to be enforced.

There's a whole parade of micro-computers that don't differentiate each other.

Re: PCI Express on the Raspberry Pi 4

#128

Post by monocasa »

megous wrote: post #76
londons_explore wrote: post #65

Earlier quoted context omitted.

Bet the broadcom SoC has a USB controller built in, but unused... You could hook it up?

https://lb.raspberrypi.org/documentation/hardware/raspberryp... This says, there's OTG controller intended to be used in "peripheral device only" mode. I haven't found datasheet for BCM2711, so it's hard to tell.

There's an XHCI controller in the device tree, but my guess is that there's some silicon bug in it, hence the third party chip off of PCIe instead.

Re: PCI Express on the Raspberry Pi 4

#129

Post by vardump »

qdot_me wrote: post #6
Jonnax wrote: post #2

That's really cool. I'm curious, would it be possible to use a modern GPU (running at 1x) on an ARM based board? Would the open source drivers that are part of the Kernel work out the box on ARM?

Hack’s creator here - it’s on my list of things to try. GPUs are notoriously hard to get to work on non-intel, having tried to get a few up on Alpha and Itaniums in the past. VideoBIOS expects to run and expects a well behaving Intel CPU to do the power-up. That said X can sometimes emulate these quite well. On ARM we’d also run into alignment issues and likely other quirks - but in principle...

> On ARM we’d also run into alignment issues...

Just don't use ARMv5 or older. ARMv6+ supports unaligned access.

Re: PCI Express on the Raspberry Pi 4

#130

Post by kllrnohj »

Millennium wrote: post #101

If a Pi is capable of this already, why not replace the Ethernet, charging, micro-HDMI, and USB ports with a boatload of type-C Thunderbolt ports (plus support for the HDMI 1.4 alt mode)? Would 8xUSB-C cost that much more than 1xUSB-C+1xEthernet+2xMicro-HDMI+2xUSB3+2xUSB2 (with no PCI Express), in exchange for a considerably more flexible device?

Because there's no where remotely close to enough PCI-E lanes off of the SoC to do that.

Thunderbolt 1/2 requires a pcie gen2 x4 connector to have enough bandwidth. The SoC in the pi4, the Broadcom BCM2711, has just a single gen2 pcie lane. 1/4th the required bandwidth for thunderbolt 1/2, and a mere 1/8th the requirement for thunderbolt 3.

To get a full 8x thunderbolt 3 connectors you need a staggering 32 pcie gen3 lanes off of the CPU. This is out of reach of all but the HEDT & enterprise platforms, to say nothing of the $5 ARM SoC chips for SBCs. Well in theory you could also use something like a Ryzen 3000 and split out the 24 PCI-E gen4 lanes into 48 gen3 lanes and then you could have your 8x thunderbolt 3 connectors, too. But that's expensive, of course.

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