No sound from second HDMI of 4të2 under RISC OS

I had some trouble with sound while connecting the machine to a friends TV and here are my findings:

- Under Unix both HDMI entries work and send sound to the monitor, but for that I have to right click on the speaker icon and tick HDMI when I switch to the other HDMI connector.
- Under RISC OS the one nearest the USB connectors does not produce any sound.

Since on Unix I have to do a manipulation to have sound after switching, I suspect that RISC OS always forces sound output to the first HDMI connector, not to the active one.

This is not a new problem: it was recognised before RISC OS 5.28 was released, and it even gets a mention on the wiki pages that I spent many sleepless nights¹ compiling.

As far as I am aware, RISC OS ignores the presence of the second HDMI connector, so it is a happy accident that the video signal happens to appear on both HDMI connectors.

Updating RISC OS to support multiple displays is on the roadmap but may take a while to get done.

¹ This may be a slight exaggeration :-)

To be fair, I the 4te2 manual does actually tell you to use the primary HDMI port, and shows a diagram of the back of the machine to identify which port is which.

I considered taping off the second one (original 4te purposely only brought out the primary, and left a blanking plate for the secondary for future expansion), but if it is being used on Linux, you might want multi monitor.

Under RISC OS (for second port), not only is there no sound, but it relies on pi mode scaling rather than RISC OS scaling for modes, which effectively limits its monitor compatibility, and (IIRC) restricts to 1080p. I suspect some of that can be fixed via cmdline.txt (and config.txt) but AFAIK RISC OS will only ever handle resolutions (and EDID) on the primary HDMI port – I don’t think you can tell it to do that for the secondary one.