Panasonic HDMI 2.1 boo-boo – dark times for Xbox Series X & nVidia users

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(For anyone who frequents the TWiT Discussion community, I posted this there as well)

I was just reading the current issue of c’t (the leading German language computer magazine). They had been doing tests with the new Xbox Series X and nVidia RTX30xx series cards. The problem is not with the Xbox or the nVidia chips.

The problem come from Panasonic. They developed the HDMI 2.1 chipset used in many amps, from Onkyo, Panasonic, Pioneer, Sony, Marantz, Denon, Yamaha & Co. and, possible Samsung TVs.

TLDR; connect the Xbox Series X, nVidia RTX30xx directly to a HDMI 2.1 capable TV and you will be fine, connect it through a current generation HDMI 2.1 AV receiver or other “switcher” and you will (probably) get a black screen. The problem occurs mainly in 4K 120Hz mode and especially with HDR.

The problem shows itself when using 4K120 HDR or 8K120 HDR. The problem seems to come with the switch from TMDS (Transition-Minimized Differential Signaling) to FRL (Fixed Rate Link) in 2.1. The signal from the Xbox and nVidia chips uses a certain pattern (*correctly*), but the Panasonic chipset interprets is incorrectly and you are left with a black screen.

c’t was testing Dirt 5 on the XBox Series X and everything was working fine, when directly connectd to an LG CX9 TV. As soon as they put it through a Denon AVR-X2700H HDMI 2.1 capable AV Receiver, they just got a black screen.

The PS5 is allegedly not affected, while it doesn’t use this specific pattern when generating images.

There is a weak point in the new HDMI 2.1 specification, but also a further bug in the Panasonic chip used by most AV Receiver manufacturers.

It seems it is a combination of FRL and DSC (Data Stream Compression) that leads to the problem in the Panasonic chipset. According to the c’t article, a firmware update for such devices is not possible. Microsoft is aware of the problem, but the first batch of Series consoles are using finalized hardware. c’t will test again using a retail example, not the preview model they received for testing.

Now they are looking to see how Microsoft and the receiver manufacturers communicate and deal with the problem. The most likely effects will be a motherboard swap for affected AV receivers or delayed release dates for receivers that aren’t already on the market, to correct the problem.

It might also be possible to use TMDS mode to generate 4K120 images with reduced defintion (TMDS has a maximum transmission speed of 18gbps, FRL runs at around 48gbps), which isn’t in the HDMI standards committee’s specification.

Another problem, with the specification, is that there is no defined standard for transmission, devices can used compressed or uncompressed feeds as they wish. Some receivers however don’t support uncompressed feeds – Xbox Series X, PS5 and nVidia RTX30xx all use uncompressed feeds.

The original article is behind a paywall, here is another site’s report on the original article (German):

https://www.heise.de/select/ct/2020/23/2028412014308611632

https://www.computerbase.de/2020-10/hdmi-2.1-bug-av-receiver-konsolen-grafikkarten/

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