[Millennium]

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?

[kllrnohj]

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.

[gnode]

Thunderbolt 3 controllers have a 4x link to provide one or two ports or 2x in the case of JHL6240. Additionally PCIe is designed to support backwards compatibility and link scaling. I don't see any reason why the 1x gen2 lane of the pi 4 couldn't host a Thunderbolt 3 port; it would just severely bottleneck the bandwidth of tunnelled PCIe links.

Even though it would be limited, a Thunderbolt 3 port would expand the connectivity of the Pi, and very few, if any, devices require the maximum bandwidth to operate at all.

[kllrnohj]

Sure but "hey here's 8x thunderbolt 3 ports just don't ever attempt to use an entire one at once kthx" isn't exactly going to be a great product story, either.

> I don't see any reason why the 1x gen2 lane of the pi 4 couldn't host a Thunderbolt 3 port; it would just severely bottleneck the bandwidth of tunnelled PCIe links.

But that's kind of literally the reason? An entire ecosystem of products assumes a reasonably high amount of bandwidth from the connector. That's its singular reason to exist. If you take away the bandwidth from Thunderbolt 3 it just becomes USB, and at that point why not just offer USB connectors which have even broader support and not as many cabling restrictions?

[gnode]

I agree that 8x Thunderbolt 3 is probably excessive, and I wouldn't want to trade away the current connectivity options as was suggested.

> If you take away the bandwidth from Thunderbolt 3 it just becomes USB

It becomes low bandwidth Thunderbolt / PCIe. You could still use it to attach PCIe devices which don't need a lot of bandwidth. GPUs can be attached for high performance compute where CPU-GPU bandwidth isn't critical. PCIe has non-bandwidth benefits over USB such as DMA and interrupts.

> why not just offer USB connectors which have even broader support and not as many cabling restrictions?

You can't attach PCIe devices via USB, but you can attach USB and PCIe devices via Thunderbolt.

[kllrnohj]

You could also do all that with just a PCI-E x1 slot and use the x1 to remote x16 connector referenced in the blog post to extend it. No reason to mess with Thunderbolt just to have any PCIE capability at all.

[Millennium]

Welp, that explains it. I stand corrected. Thanks.

[joey_bob]

A lot of the benefit of the rpi is the built in IO. Would the rpi still be cost effective without it? Not for many of the IoT projects that make the rpi so popular.

[Millennium]

I didn't propose replacing the GPIO, or the camera port, or the other display port. I'm talking specifically about the other ports around the sides of the device, which are already used for more traditional computer-y things. Of course the Pi needs to retain its built-in low-level I/O, but it has another side to it too, and that's the side I'm talking about using Thunderbolt with.

[buildbuildbuild]

A RasPi-compatible USB GPIO breakout adapter would be a cool product.

[zokier]

Because people do not want to deal with gazillion dongles

[gambiting]

And not just because all those dongles would significantly increase the cost of a relatively cheap device.

[gnode]

A Thunderbolt port or two would be a nice addition to improve connectivity options, but sacrificing the other ports and requiring expensive dongles goes against the aim of being a cheap computing platform.

Additionally, this would require adding more PCIe lanes to the SoC, as there isn't bandwidth to provide the two 4K HDMI outputs and the other connectivity would be severely bottlenecked.

[theonlyklas]

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.

[kingosticks]

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

[jankotek]

Dongles would cost more than Pi