HDMI to VGA

My current setup has an ARMX6, a Dell laptop, an RPC and an older desktop PC.
The ARMX6 has HDMI output. The laptop has HDMI off the docking station, the other two are VGA. I use a 4-port VGA and USB switch, and this setup has worked for several years. I run the ARMX6 at 2560 × 1440 @ 45Hz, using a small HDMI to VGA adapter. Recently while I was moving things around the adapter got swapped for an apparently identical one. Now the monitor loses lock every few seconds, and takes its usual 10 seconds to resync.
Once I put a different adapter in place (might have been the original, not sure) it is working again, though the resync time seems to have increased.

It’s apparent that 2560×1440 is pushing the converter to its limit. I’m wondering how to get a more stable setup.

Option 1 is to try and find an HDMI-VGA adapter which can produce a stable 2560×1440 display. None I’ve browsed for seem to go above 1920p.

Option 2 is to replace the VGA 4-port switch with an HDMI switch, and buy a VGA to HDMI adapter for the RPC, and either abandon the old desktop (VGA only) or buy an adapter for that too. The adapters I’ve found are around £20. An HDMI 4-port with USB looks like £80.

Can anyone suggest anything for option 1?

Isn’t 1920×1080 the max resolution that VGA can handle?
I suppose, obviously not, as you’ve had more than that being pushed through a VGA.

“Can anyone suggest anything for option 1?”

If you look to the future, you probably won’t buy VGA devices anymore. You will continue to have to deal with HDMI. Don’t adapt your solution to what you have, but to what the future holds, is my suggestion.

Isn’t 1920×1080 the max resolution that VGA can handle?

With the right equipment (i.e. not artificiality limited PC stuff) it will do more.

My former Iyonix could drive the the VGA input of my 2560×1440 LCD, with my old CRT it used to do 2048×1536, and it could just about manage 2560×1920.

Isn’t 1920×1080 the max resolution that VGA can handle?

<pointlessly pedantic> 640×480 is the maximum VGA can handle </>

Assuming you mean the VGA connector (as opposed to the VGA video mode), it is an analogue connector using separate wires for R, G, B, and H and V sync. The colours are 256 discrete levels from 0v to 0.7v.

In theory, a good video adapter can run a pixel clock up around 400MHz or so. So it ought to easily cater for 2560×1440 at 60Hz which when interlaced and with margins is about 345MHz pixel clock (so has leeway), which is more than can be catered for by DVI and HDMI 1.whatever.

You could go faster, but your problems are going to be crosstalk/capacitance in the wires, the ability of equipment to lock into and reliability track such tiny signals changing so rapidly, and – of course – finding something willing to even work with analogue signals like that.

Druck, of course, turns this up to twelve…

1920×1080

Non interlaced, 60Hz, pixel clock of 173MHz.

2560×1440 LCD, with my old CRT it used to do 2048×1536, and it could just about manage 2560×1920.

~312MHz, ~267MHz, and (damn!) ~420MHz (out of capabilities of HDMI 2.1 FRL1).

My hat of to Druck, I think that’s the fastest I’ve heard of an analogue VGA interface going at.

I think the 2560×1920 was only at 56Hz, so probably around 400MHz of clockiness.

I think the 2560×1920 was only at 56Hz, so probably around 400MHz of clockiness.

As I said at the start, I have an ARMX6 producing 2560 × 1440 @ 46Hz, going through a converter to the VGA input of a monitor. I imagine that is a similar clock rate. The monitor is happy with it (for some definition of happy) but only provided a selected HDMI-VGA converter is used, so it’s apparent that the signal is marginal in some way.

I’ve decided to bite the bullet and I’m awaiting the delivery of £97 of hardware to do this differently – using HDMI where it exists and convert VGA to HDMI where necessary. I just hope it works without anything unexpected spoiling the party. It will at least free up some more converters to use with the RPIs and my significant collection of VGA-only monitors.

So I now have an HDMI KVM, working on the ARMX6 and the Windows10 laptop.

The RPC is giving trouble. It’s running RO4.02.

1. The VGA output only shows a display if a physical monitor is connected while it boots up. If I then transfer the connection to the KVM, I get a display. However there’s no display if the KVM video is connected during booting.

2. The VGA-HDMI adapter is USB powered. However powering it from the Unipod causes a USB lockup. Fortunately there is a powered hub close, and using that is better.

3. The combined USB keyboard and mouse connection is not recognised. However a keyboard plugged into the other USB port of the Unipod does work, so at least it doesn’t crash the USB stack, which is a weakness I’ve found before with the Unipod. It locks up for example on recent Logitech wireless trackballs, though an early model does work.

Any suggestions? For example, is there more recent Unipod firmware available? Does an alternative USB module work, and if so, which one? How do I get the VGA output to work without connecting a physical monitor?

@ Alan A.,

1. The VGA output only shows a display if a physical monitor is connected while it boots up. If I then transfer the connection to the KVM, I get a display. However there’s no display if the KVM video is connected during booting.

To solve this problem, you can use one of these devices:

https://www.amazon.co.uk/dp/B07YN42M1V

They are cheap and, in some cases, you can also pick one with high resolution emulation. I normally use only HD and that is because that’s way more than a RiscPC can work fine with. Those devices make the RiscPC believe there is always a connected monitor and when you switch your KVM to the RiscPC they give control to the KVM.

3. The combined USB keyboard and mouse connection is not recognised. However a keyboard plugged into the other USB port of the Unipod does work, so at least it doesn’t crash the USB stack, which is a weakness I’ve found before with the Unipod. It locks up for example on recent Logitech wireless trackballs, though an early model does work.

The combined USB and keyboard has always been a problem AFAIR. Below some ideas to work around this problem:

- Use a USB mouse and keyboard switcher before your KVM (if, for example the KVM is close to your RiscPC), this allows you to have your keyboard and mouse connected to the KVM (for all your other devices) and when you need to connect the keyboard and mouse to your RiscPC you use the two switchers instead of the KVM. It’s not the best approach but it’s certainly the cheapest!

- Replace your KVM with one that support TRUE PS/2 protocol. Those are a bit rare these days, Startech still makes some, and they aren’t the cheapest, BUT they definitely work with the RiscPC (I have one in my Acorn’s Rack) and even with the Archimedes range, and do not use the UniPOD (making your machine a looooooot more stable).

Let me know if you are interested on the 2nd option and I’ll search for a link to the KVM I use.

Also keep in mind that, IIRC, having Podules or stuff that have IRQs during boot enabled maybe the source of RISC OS crashes, aka the issue isn’t necessarly the Podule. RO’s boot has always been a bit weak on the RiscPC.

HTH

That’s given me some ideas. The old VGA KVM does negotiate with the VGA port, and its combined keyboard and mouse signals do work with the RPC/Unipod. So I may be able to use that as the second switch. If it works it also gets over the limitation on the hdmi kvm of only having two usb inputs.
It’ll be a few days before I can do another upheaval to test it though.