With FW platforms already shipping (FW13 AMD, plus FW16 coming soon) that support HDMI 2.1 and DisplayPort 2., how soon should we expect FW to release new expansion cards that support these new standards?
FW seems to have worked quickly to release revisions to the existing HDMI and DP cards but that was motivated by something completely different.
The DisplayPort Expansion Card is mostly a passive passthrough of the DisplayPort signals from the processor, so it supports whatever DisplayPort version the processor supports.
At first Framework advertised the DisplayPort Expansion Card as supporting DisplayPort 1.4 (since at the time that was what was supported by the processors Framework were using), however it has since been updated to say “The DisplayPort Expansion Card passes through DP Alt Mode directly from the Mainboard, enabling support for the maximum DisplayPort version and monitor resolution supported by the processor.”
So the DisplayPort Expansion Card already automatically supports the latest DisplayPort version supported by the CPU.
The CPU doesn’t support outputting HDMI over USB-C, so the HDMI Expansion Card is basically a DisplayPort Expansion Card with a chip that translates DisplayPort into HDMI. So a new HDMI Expansion Card will be needed to get newer HDMI versions.
Thanks, that would be a great outcome and I would love for them to clarify that in the fine print on the product page.
I noticed that change too but never occurred to me that the pass-thru nature could support such an increase in bandwidth!
Yep, with a little bit of circuitry to tell the laptop to supply DP signals to the USB-C port.
TBF, the expansion ports are limited to 40Gbps and full bandwidth HDMI 2.1 is 48Gbps, so some kind of DSC would need to be supported I think. I have absolutely no idea if the iGPU has that feature but I also don’t see the need since the iGPU is so weak. Anything that the iGPU can do can be done with the reduced bandwidth currently possible. Unless you have a different use case?
Isn’t that only when they’re used in Thunderbolt 3 mode?
@jschievink The ports are TB4. The expansion cards just convert that signal into whatever it is they are designed to convert it to. The inherent limitation will always be 40Gbps, no matter what the expansion card supports.
USB-C alternate modes don’t work like that, they reconfigure the lanes of the connector to carry an alternate signal directly, without encapsulating it in thunderbolt.
A TB4 connector is rated for 80 Gbps (plus a separate USB 2.0 connection, but I’m ignoring that because it has its own dedicated bandwidth).
The Thunderbolt 4 protocol splits that bandwidth into 40 Gbps in each direction, however DisplayPort alt mode (where the connector is carrying a DisplayPort signal directly instead of Thunderbolt) doesn’t have that restriction because DisplayPort has no need for symmetric bandwidth. (Thunderbolt 5 also supports asymmetric bandwidth)
I strongly suspect that one of the reasons why the DP 2.0/2.1 UHBR20 is exactly 80 Gbps is so it can take full advantage of the 80 Gbps available through a cable rated for Thunderbolt 4.
The big problem I see with the HDMI 2.1 cards is that that spec is being withheld from Linux platforms. The HDMI card would have to produce a DP signal and convert it to HDMI to support it properly as I understand it.
I don’t know enough about the spec to say, but if no DP conversion was done to lower the cost and power demand of the card, the card could support HDMI 2.1, but have to be limited back to 2.0 on Linux platforms.
At that point, assuming that the Linux community either doesn’t entirely boycott HDMI and use DP, or the HDMI forum changes their mind and allows 2.1, it would make more sense for Framework to sell the HDMI 2.1 using DP conversion beside a revision of the already produced 2.0b cards to 2.1 without conversion.
I don’t think selling two versions is a financially supportable service
That is how the current DP 2.0b card works.
The spec does not allow above HDMI 1.4 without any conversion and the HDMI forum (the group responsible for the HDMI spec) has officially stated that they will never update it to allow above HDMI 1.4.
So unless the HDMI forum changes their stance Framework will always use DP conversion. As you point out this is also great for Linux compatibility due to other decisions the HDMI forum has made (limiting 2.1).
Edit: IIRC many Intel dGPUs do use the DP conversion technique. Afaik they do it in order to avoid the cost of including HDMI support directly on the GPU core (cheaper to use separate chips for it and only on products that need it), but it works for getting around the HDMI 2.1 limitations with Linux.
Ah, thank you for the clarification. I was not aware that Framework was already having to do DP conversion on the current cards. I though that above 2.0b spec was being withheld from the platform, not above 1.4.
Above 2.0b is being withheld from open source Linux drivers.
Above 1.4 is being withheld from being carried over USB-C. Since USB-C is how the expansion cards connect to the computer that means that expansion cards have to use DP conversion.
Afaik no product that actually carries HDMI over USB-C was ever mass produced, not even at HDMI 1.4. This is because the HDMI 1.4 over USB-C spec didn’t come out until after the DisplayPort 1.4 over USB-C spec was already available and had over triple the bandwidth and supported better compression (allowing it to use that bandwidth better).
So from the very beginning USB-C to HDMI adapters (including the Framework Expansion Card) used DP conversion.
USB-C does not support the DP++ output. Not even enough pins (you could argue that USB-C is already missing one pin for super easy DP output, making all those bidirectional USB-C DP cables harder).
DP alt mode only allows native DP output. And the HDMI alt mode standard that would have allowed native HDMI output has already died.
And due to the limitations and current problems of DP-HDMI conversion, such a conversion solution may forever be less capable than native DP output. And the few features HDMI has that DP does not, Vesa could easily add to DP if HDMI dies out. Or computers have barely/never supported those features anyway (think CEC and ARC).
Thank you. The limit to 1.4 wasn’t making sense to me as I was sure that 2.0b was working and I was using it on my desktop, so I started looking online to find a muddy area. I couldn’t find the clarification as to why the divide over 2.0 and 1.4. Everything seems to tend to be about the 2.1 withhold by HDMI forum, and their prevention of open ports for the spec, most notably, by AMD.