Spectrum Computing

MatGubbins wrote: ↑Wed Sep 07, 2022 6:09 pm Although I don't own an N-Go or Next, I'll ask the question of how are you connecting the N-Go to your screen - HDMI, VGA or some other way?
The N-Go and Next experts will then give you some feedback,

Also have a good read of every comment from this page
viewtopic.php?t=1131&start=370

Multicolour/Nirvana only works in VGA or RGB timings at 50Hz.

The reason is that HDMI or 60Hz both necessitate different video timings, and without a scanbuffer to hold and resample the picture, the timings of the Next have to be bent to have a different number of Ts per line, lines per frame, and frames per second in order to get close enough to the HDMI spec for most displays to display them. The first buggers up multicolour programs expectations that they’re running at exact 48K or 128K timings. The second leaves significantly less Ts per frame. My Nirvana games all crash at 60Hz because they overrun the frame, but Stormfish was ok last time I tested it.

The reason the Next doesn’t have a scanbuffer is simply that there isn’t room for one in the FPGA chip. It takes quite a bit of circuitry and BRAM to implement one.

This is actually a common problem other retro systems have too, as not all of them have a hardware scanbuffer chip or a large enough FPGA.

In the future it will be possible to address this. One possibility is to have a separate standard Spectrum core, without the Next-specific features. This has room for a scanbuffer. This core already exists as a proof of concept and works great, but the multicore infrastructure is still being worked on, so isn’t quite ready for general use yet.

Another possibility is to split the core into separate cores for VGA and RGB, which will also free up some room in both, perhaps enough for a rolling partial-frame scanbuffer. This one also needs some new infrastructure to make it truly seamless to switch between them.

You can also use RGB timings with a SCART cable and a RGB-SCART/HDMI convertor, if you’re unlucky enough to have an HDMI-only display.

For now multicolour games (including Denis’s Pentagon Nirvana) do work great in VGA and RGB modes.

stupidget wrote: ↑Wed Sep 07, 2022 8:05 pm Not sure if this is relevant but all those games use the Nirvana multicolour engine so I’m assuming that the n-go doesn’t support this capability.0

oO cozy Oo wrote: ↑Wed Sep 07, 2022 7:07 pm Why have a Next or N-go if they cannot emulate a spectrum properly.......

So now i have to run in VGA now Im sad now....

oO cozy Oo wrote: ↑Wed Sep 07, 2022 7:07 pm So now i have to run in VGA now Im sad now....

oO cozy Oo wrote: ↑Wed Sep 07, 2022 4:40 pm Hi Everyone,
Got an n-go last week and have been playing around with some zx 128k games and came across Old Tower from retro souls not playing the game as it should, its slow and the graphics are not correct, also Multidude.
I`ve gone through all the setting and also formatted 2 cards and also used new next firmware and tbblue and re downloaded n-go softare ??
anyone else having these problems..Just loaded Buzzsaw+ and the rainbow wave on the menu screen is not right

thanks cozy

-48K- wrote: ↑Tue Jan 17, 2023 9:15 am @Chris23235 May I ask whcih brand/model of HDMI>VGA converter you are using?

Chris23235 wrote: ↑Tue Jan 17, 2023 1:54 pm Hi, I use the OcioDual VGA2HDMI converter.

-48K- wrote: ↑Tue Jan 17, 2023 9:15 am May I ask whcih brand/model of HDMI>VGA converter you are using?

scandoubler=0
50_60Hz=0
timing=0

Robhawk wrote: ↑Tue Jan 17, 2023 2:40 pm Just for awareness I ordered one of these around a month ago from Amazon and it did not work at all - no signal of any sort at the TV. They are not a fortune but you may need to try a couple.

Chris23235 wrote: ↑Tue Jan 17, 2023 3:56 pm Did you try a different USB power cable?

Seven.FFF wrote: ↑Tue Jan 17, 2023 4:39 pm The OcioDual appears to be 60Hz only, so the TV would have to understand HDMI60 at the resolution it outputs. The HDMI spec doesn't require TVs to support 50 and 60 in every single resolution the spec covers - only one 50Hz and one 60Hz each. We've encountered many TVs that don't do what are needed for various convertors or the native HDMI output.



A related question is whether the convertor will accept VGA50 and convert it to HDMI60, or whether it needs the input to be VGA60 too. In that case you'd need to set the Next to output 60Hz in order to get a picture. Of course that effectively puts the Next in US Timex Sinclair timings, which are quite different from UK 50Hz Spectrum timings. Which would be no good when the end goal is accurate timings.

Even if it does accept VGA50 input, @Chris23235 would need to put the next into VGA50 timing 0 to use it. Just plugging the converter in when the Next is set to output HDMI wouldn’t work.

Chris23235 wrote: ↑Tue Jan 17, 2023 3:56 pm Did you try a different USB power cable?

Robhawk wrote: ↑Tue Jan 17, 2023 5:54 pm I did try with a PI PSU but still no avail.

Perhaps it’s an issue and I need to set my N-GO to the VGA50 timing 0 setting? I’m pretty sure I did not do this.