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CAC-1080: NVidia Failsafe after boot

Updated on 15-11-2023 in Adapters and Cables
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12 on 01-10-2023

Hi there,

on my Windows 11 machine I have 3 monitors connected to a GTX3080 Ti. The primary one is connected using DP1.4 cable and the other ones are connected using the CAC-1080 DP to HDMI adapter (reasons for this later, but this shouldn’t be the main topic here).

The problem:

Everytime after reboot (or wake from hibernation/standby) the monitors connected using the CAC-1080 adapter are not recognized correctly. They appear as “nvfailsafe” monitor in the device manager and resolution is 640×480. Replugging the adapters on the DP side fixes this issue, but only until the next reboot.

I’m already running the latest NVidia driver, did a clean install of it, etc. Nothing helped so far.

I’ve as well tried out different DP to HDMI adapters (from Cable Creation) and these do not have this specific problem (unfortunately they have other issues which make them nearly unusable for me).

Question:

Is there anything I can do to improve this situation?

Reasons for using DP to HDMI as a workaround:

I bought 3 DSC monitors (that do not have an option to disable DSC) without knowing that NVidia cards are currently limited to a maximum of 2 DSC monitors.

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Baak 0 on 03-10-2023

Does this also happens when disconnecting one of the other displays? Which displays are they?

The RTX3080TI has 3 DP ports, can’t you use 3 direct DP connections?

Please provide a link with the info where it’s stated the 3080TI does not support over 2 DSC monitors. I haven’t heard about this before.

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flobernd 3 on 03-10-2023

Hi @Baak, thanks for your reply.

The DSC limitation is documented here:
https://nvidia.custhelp.com/app/answers/detail/a_id/5338/kw/dsc

> When a display is connected to the GPU and is set to DSC mode, the GPU may use two internal heads to drive the display when the pixel rate needed to drive the display mode exceeds the GPU’s single head limit. This may affect your display topology when using multiple monitors. For example if two displays with support for DSC are connected to a single GeForce GPU, all 4 internal heads will be utilized and you will not be able to use a third monitor with the GPU at the same time.

The screens are all CoolerMaster GP27-FUS and I can confirm just 2 of them connected works fine. Limiting resolution/refresh-rate to 4K@60Hz does not disable DSC which still limits me to 2 monitors.

I’m in contact with CoolerMaster to add an option to disable DSC/switch to DP1.2 mode, but if ever happen, this will take a while so Im in need of a workaround for now.

flobernd on 03-10-2023

That being said, the Failsave issue only occurs with the C3D adapters. The cable creation ones are working better in that regard, but switching times are extremely high on these (takes 10-15 seconds for monitors to get recognized after connecting them). This is important for me as I’m using a KVM switch (before you ask: I as well tested without the KVM and the problem still persists).

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Baak on 03-10-2023

Is there anyway you could draw out your whole setup? Because I can not make anything out of it sorry. Do you use a laptop or PC? Or both? Where is the adapter connected KVM or GPU?

Which GPU is it?

Why would you use an adapter (DP to HDMI2.0) on the GPU if the Display supports DP1.4 or HDMI2.1. My suggestion would be cut out the adapter and use cable alone.

If you look at the below topic you see this person is driving 3x 4K @ 120Hz. So it should not be an DSC issue.

https://insights.club-3d.com/thread/cac-1085-problem/

 

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flobernd on 03-10-2023

@Baak Thanks for trying to help. I try to describe it as clearly as possible:

  • GPU: GTX 3080 Ti (Desktop machine, Windows 11)
  • Monitors: 3x CoolerMaster GP27-FUS (DSC can’t be disabled on these)
  • Requirement: All monitors must be connected to DP on the GPU side (because I’m using a DP KVM switch)
  • To simplify: Don’t worry about the KVM. I tested it without the KVM switch as well and the results are identically
    • 2 monitors on DP work fine without the adapters
    • 1x 4K@144Hz on DP + 2x 4K@60Hz with CAC-1080 on DP works fine as well (but gives me the Failsafe issue on boot)

Regarding the other post: Maybe a 3090 is more capable than a 3080 Ti, but the linked NVidia help center article as well phrases this in the following way:

GPU may use two internal heads

The “may” indicates that it might use 2 internal heads (which will limit me to 2 connected monitors), but does not necessarily have to.

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joevt 1 on 03-10-2023

A DisplayPort to HDMI 2.0 adapter is way to exclude DSC. You tried that with the CAC-1080 but got the Failsafe issue.

You could use a DisplayPort 1.2 MST hub to disable DSC. DisplayPort 1.2 has slightly more bandwidth than HDMI 2.0 and you don’t have to worry about HDMI conversion issues.

There are also DisplayPort 1.4 MST hubs which may have older firmware that does not support DSC. I had a couple of those but have since updated their firmware to support DSC. If you get one that supports DSC, you might be able to get a firmware that removes DSC support.

You should ask Nvidia to add an option to disable DSC to eliminate the issue described in
https://nvidia.custhelp.com/app/answers/detail/a_id/5338/kw/dsc

DSC is required for 4K144. DisplayPort 1.4 without DSC can do 4K120 but only at 8bpc. I think 10bpc is required for HDR.

flobernd on 04-10-2023

Thanks for your reply! This is very helpful. Can you recommend a specific vendor for a DP1.2 MST hub?

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joevt 2 on 04-10-2023

Club-3d has MST hubs. They have DisplayPort 1.4 and 1.2 models. I don’t know if their DisplayPort 1.4 MST hubs support DSC or not. I have not tried any of them.

CSV-7200 DisplayPort 1.4 DisplayPort to Dual DisplayPort (no DSC?)
CSV-7220 DisplayPort 1.4 DisplayPort to DisplayPort + HDMI (DSC)

CSV-1550 DisplayPort 1.4 USB-C to Triple DisplayPort (DSC)
CSV-1555 DisplayPort 1.4 USB-C to Dual DisplayPort (no DSC?)
CSV-1552 DisplayPort 1.4 USB-C to DisplayPort + HDMI (DSC)

CSV-6400 DisplayPort 1.2 DisplayPort to Quad DisplayPort (no DSC)
CSV-6200 DisplayPort 1.2 DisplayPort to Dual DisplayPort (no DSC)

I would try the CSV-7200 or the CSV-6400.

The MST hub I did try was the Delock 87737. I had to use a firmware update to get DSC support.

Probably all the MST hubs use a Synaptics chip.
https://www.synaptics.com/products/video-interface-ics

All the MST hubs I tried do not seem to be able to decompress 10bpc. So if you get an MST hub that supports DSC, then maybe you can make it not output DSC by switching output to 10bpc in the Nvidia control panel. 10bpc is usually required for HDR.

Not being able to use DSC for 10bpc reduces greatly the number of displays you can connect to the MST hub. But you’re not using the MST hub to connect more displays and you don’t want DSC. You’re using the MST hub to force DSC to not be used.

An MST hub isn’t really useful for connecting more displays to an Nvidia GPU because the Nvidia GPU can only connect 4 displays and usually already has enough ports for that. An MST hub is more useful for laptops that don’t have enough ports.

An MST hub can convert fast&narrow DisplayPort to slow&wide DisplayPort. For example, a DisplayPort to Dual Link DVI adapter is HBR x4 but a USB-C dock is usually HBR3 x2. The MST hub can convert HBR3 x2 to HBR x4 so that the adapter can achieve 2560×1600 60Hz, otherwise the adapter would be limited to 1920×1200 when connected to the dock.

flobernd on 05-10-2023

Thanks a lot, this is a very informative post! I’ll give it a try.

Especially your observation about 10bit is interesting.

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flobernd on 06-10-2023

The CSV-7200 works like a charm! At least 4K@60Hz is stable (for now this will be sufficient). 120Hz works on one of the  screens, but causes massive flickering and does not work on the other screen at all. Not sure what’s going on. Exact same HBR3 Club3D cables used for all monitors.

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joevt 0 on 06-10-2023

There is a small bandwidth overhead with MST hubs. You may find that using CRU (Custom Resolution Utility) to create a 4K117 mode might help. Just decrease the refresh rate until it works. Or start from 110Hz and increase the refresh rate until it stops working.

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