Totoze
Posts: 3
Joined: Mon Jun 24, 2019 3:07 pm

Respberry Pi 4 B , Two USB 3.0 eGPU

Mon Jun 24, 2019 10:52 pm

A USB 3 port can transfer 5 GB/S , there are 2 USB 3 ports on the pi. That's 10 GB / s going in. Same as a thunderbolt connection. So theoretically would it be possible to connect a simple external GPU to a Respberry Pi 4 ?
Last edited by Totoze on Tue Jun 25, 2019 7:53 am, edited 1 time in total.

User avatar
HawaiianPi
Posts: 4466
Joined: Mon Apr 08, 2013 4:53 am
Location: Aloha, Oregon USA

Re: Respberry Pi 4 B , Two USB 3.0 eGPU

Mon Jun 24, 2019 11:22 pm

That's assuming the USB ports are not connected through a hub chip and single USB interface on the SoC (like previous models).
My mind is like a browser. 27 tabs are open, 9 aren't responding,
lots of pop-ups...and where is that annoying music coming from?

Andyroo
Posts: 3841
Joined: Sat Jun 16, 2018 12:49 am
Location: Lincs U.K.

Re: Respberry Pi 4 B , Two USB 3.0 eGPU

Mon Jun 24, 2019 11:28 pm

Just because you can equal the bandwidth, it does not mean the protocol or drivers exist for dual channel vs single channelled alone an application or games that can use it :lol:

You can already get USB adapters up to 4K :o
Need Pi spray - these things are breeding in my house...

Andyroo
Posts: 3841
Joined: Sat Jun 16, 2018 12:49 am
Location: Lincs U.K.

Re: Respberry Pi 4 B , Two USB 3.0 eGPU

Tue Jun 25, 2019 2:16 am

You cannot actually reach the bandwidth. USB3 may be spec’d for 5GB/s but
USB is provided via an external VLI controller, connected over a single PCI Express Gen 2 lane, and providing a total of 4Gbps of bandwidth, shared between the four ports.
From: Blog announcement

Saying that, I’m not going to be able to get that throughput to the disks I would look to connect :lol:
Need Pi spray - these things are breeding in my house...

Totoze
Posts: 3
Joined: Mon Jun 24, 2019 3:07 pm

Re: Respberry Pi 4 B , Two USB 3.0 eGPU

Tue Jun 25, 2019 7:52 am

So if it can't give nearly 5 GB why call it USB 3.0? I guess this will at least make connecting a real drive to the Pi better. Still somewhat disappointing that it's not actually what it seems from the upfront specs.

dickon
Posts: 356
Joined: Sun Dec 09, 2012 3:54 pm
Location: Home, just outside Reading

Re: Respberry Pi 4 B , Two USB 3.0 eGPU

Tue Jun 25, 2019 8:58 am

Totoze wrote:
Tue Jun 25, 2019 7:52 am
So if it can't give nearly 5 GB why call it USB 3.0? I guess this will at least make connecting a real drive to the Pi better. Still somewhat disappointing that it's not actually what it seems from the upfront specs.
Because USB 3 is much more than just a speed boost over USB 2.

User avatar
bensimmo
Posts: 4129
Joined: Sun Dec 28, 2014 3:02 pm
Location: East Yorkshire

Re: Respberry Pi 4 B , Two USB 3.0 eGPU

Tue Jun 25, 2019 9:26 am

yep it's a speed boost AND it's also a blue socket ;-)

Andyroo
Posts: 3841
Joined: Sat Jun 16, 2018 12:49 am
Location: Lincs U.K.

Re: Respberry Pi 4 B , Two USB 3.0 eGPU

Tue Jun 25, 2019 12:21 pm

Its a significant change to deliver the speed increase:

1) Obviously the colour difference (should be red* as the 'red wunz go faster')
2) Power delivery - up to 900mA compared to 500mA (device build depending of course) to allow for faster / larger devices
3) USB 2 is unidirectional data flow (i.e. send or receive) where as USB 3 can do both at the same time
4) USB 3 has more wires (9 off the top of my head) compared to 4 for USB 2

The connectors are supposed to be more reliable BUT an user can still break them...


* USB 3.1 is spec'd as red but I think USB-C kind of got in the way :lol:
Need Pi spray - these things are breeding in my house...

User avatar
clicky
Posts: 309
Joined: Thu Oct 25, 2012 7:34 am

Re: Respberry Pi 4 B , Two USB 3.0 eGPU

Tue Jun 25, 2019 1:02 pm

Totoze wrote:
Tue Jun 25, 2019 7:52 am
So if it can't give nearly 5 GB why call it USB 3.0? I guess this will at least make connecting a real drive to the Pi better. Still somewhat disappointing that it's not actually what it seems from the upfront specs.
USB 3 specification allows speeds up to 5GB and doesn't prescribes it as minimum bit rate. You can easily still have USB 3 device and it not to use speeds faster than 480 Mbps (or much slower). Speed is not dictated only with maximum throughput of the 'pipe' - what would you say for USB 3 to SATA adapter with old spinning disk on it barely scratching 20-30% (if that much) of the bandwidth? LOL ;)

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 23083
Joined: Sat Jul 30, 2011 7:41 pm

Re: Respberry Pi 4 B , Two USB 3.0 eGPU

Tue Jun 25, 2019 1:13 pm

Totoze wrote:
Tue Jun 25, 2019 7:52 am
So if it can't give nearly 5 GB why call it USB 3.0? I guess this will at least make connecting a real drive to the Pi better. Still somewhat disappointing that it's not actually what it seems from the upfront specs.
As above, but what should it be called? It's not USB 2, it's way faster than the maximum spec of USB 2 and it uses the USB3 specification wiring. How about USB2.9?

Might be worth considering that many many USB3 devices never hit the THEORETICAL maximum bitrate....would also be interesting to know how many USB3 hosts are actually limited in some way to less than 5GB/s. I'd guess almost all of them.....
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Contrary to popular belief, humorous signatures are allowed. Here's an example...
"My grief counseller just died, luckily, he was so good, I didn't care."

louis114
Posts: 1
Joined: Wed Jun 26, 2019 1:26 pm

Re: Respberry Pi 4 B , Two USB 3.0 eGPU

Wed Jun 26, 2019 1:29 pm

So, what's the conclusion for eGPU? Can it connect a eGPU?

Return to “General discussion”