ZX Spectrum Next Discussion

For experts to discuss very technical stuff and newbies to ask why the Spectrum they bought off ebay doesn't work.
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R-Tape
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Re: ZX Spectrum Next Discussion

Post by R-Tape » Wed May 08, 2019 10:45 am

Hehe, probably the first time #MatthewSmith was trending on twitter and it wasn't about Doctor Who!

Whatever happens (and this may not be soon enough for some), the Next really, really, really has to be finished and on people's desks this year.
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Re: ZX Spectrum Next Discussion

Post by Vampyre » Wed May 08, 2019 12:33 pm

It's not finished? I've seen one in action in the flesh via someone who backed it???

EDIT: Oh, is it the full one with the keyboard that's not ready? The one I saw was just the motherboard.
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Re: ZX Spectrum Next Discussion

Post by Bizzley » Wed May 08, 2019 12:36 pm

Some of the comments made by Jim Bagley and Mike Cadwallader in the repost by @toot_toot certainly do seem a little worrying. With the Next having officially been promised for delivery before end Q2 2019 (June 30th) you would expect everyone on board with the project to at least stand by that date, be it eventually right or wrong. Bagley and Cadwallader's repeated remarks that they are as lost about this as the rest of us means that they may not be as closely involved with the initimacies of the project as backers think they are. It also seems from what they're saying that behind the scenes it's pretty much a one-man-band operation with Henrique Olifiers calling all the shots.

Mike Cadwallader's admission that KS Updates look better when there's a "happy ending" may hold true while everything is on schedule but when there's no definite indication that one and a half years past the due delivery date the boxed Next it may still not appear then I think backers deserve more than that. Apart from April's eulogy to Rick Dickinson that's all we've heard from Olifiers since March.
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Re: ZX Spectrum Next Discussion

Post by ZxSpence » Wed May 08, 2019 2:14 pm

It is indeed worrying, and with the increasing aggression towards anyone who asks a question it's looking very bad indeed.

Hopefully the worries will come.to nothing but when he whose back catalogue turns heads but whose ego bends light deploys himself to attack perceived critics it only makes it worse.

Here's hoping for a.happy ending.
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Re: ZX Spectrum Next Discussion

Post by Spud » Wed May 08, 2019 6:17 pm

I tried it out at the expo and was very impressed. I didn’t back it but wish I had. I will if they do a second run.

Jim B seemed to be a very nice bloke too.
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Re: ZX Spectrum Next Discussion

Post by ZXDunny » Sun May 12, 2019 10:24 pm

Looks like they're re-doing the keyboard membranes now?

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Re: ZX Spectrum Next Discussion

Post by Bizzley » Sun May 12, 2019 11:06 pm

ZXDunny wrote:
Sun May 12, 2019 10:24 pm
Looks like they're re-doing the keyboard membranes now?
It's not just the Right Cursor key that doesn't work reliably, it's quite a few composite key presses that are prone to failure as you can see from the picture and mentioned in the latest Update. They are going to try three different designs for the new contacts and hope that one of them does the job but they won't know if any of them work until they get the results back. That to me sounds more like desperation than having a definite and workable idea of how to fix the problem.

Someone has posted on the KS Comments "Is there a backup plan?" in case these fixes don't work and it's a very good question, what indeed does happen if the Next keyboard just plain won't work reliably whatever they come up with?
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Re: ZX Spectrum Next Discussion

Post by Alcoholics Anonymous » Mon May 13, 2019 4:30 am

Bizzley wrote:
Sun May 12, 2019 11:06 pm
It's not just the Right Cursor key that doesn't work reliably, it's quite a few composite key presses that are prone to failure as you can see from the picture and mentioned in the latest Update. They are going to try three different designs for the new contacts and hope that one of them does the job but they won't know if any of them work until they get the results back. That to me sounds more like desperation than having a definite and workable idea of how to fix the problem.
That is exactly what the problem is. It should be made clear that the keyboard is not designed by the next team - it is by a keyboard manufacturer which has plenty of experience building keyboards. They were sure the keyboard would perform well once it was machine assembled rather than hand assembled and they were wrong. Two semi-circle halves as contact means preference for one side or the other in striking leads to one contact being made before the other. If the difference in time is significant this can't be covered up in hardware without affecting the responsiveness of the unshifted key. And that's where it is.

The length of delay is not because there's anything being hidden; it's because the next is a low volume project that has bottom priority for suppliers. They deal with it after higher priority customers are dealt with. Nothing may happen for weeks. Now that they see the machine assembled keyboard does not work as expected, hopefully they have reason to spend some more urgent attention.
Last edited by Alcoholics Anonymous on Mon May 13, 2019 5:01 am, edited 1 time in total.
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Re: ZX Spectrum Next Discussion

Post by Alcoholics Anonymous » Mon May 13, 2019 4:57 am

zxbruno wrote:
Wed May 08, 2019 1:40 am
I read somewhere else that the designer of the hardware ignored the concerns of people who pointed out a few flaws and recommended addressing them. Does anyone know if they were addressed? I don't know anything about hardware, so I don't understand the details. But it was something about the danger of having the FPGA directly connected to something, and bad implementation of HDMI.
The hdmi implementation is not "bad". The problem lies in hdmi televisions not fully implementing the hdmi spec. hmdi tvs should be flexible in video timing but in fact some are not and there are still models out there that only support a list of example timings that the hdmi spec supplies. Most devices and broadcasts will be using one of those from the list.

The problem with the spectrum is the video timing is connected to the pal signal which does not line up with one of the hdmi listed examples. You can deal with this mismatch two ways. One way is you can store frames generated by the spectrum side in memory and then generate an hdmi signal from that by interpolating between frames. This is what many 3rd party devices do. The next does not have the fpga memory available to do this. Instead the signal is generated live without delay by modifying the video timing of the machine so that an hdmi signal that works on the majority of tvs tested works. TVs that fully implement recent(ish) hdmi specs should have no trouble; this modified timing will mean even more hdmi tvs are compatible. It's still not 100% but it seems to have large coverage. You may remember the problems reported after the boards were delivered. It was the experimentation during this time that led to the current implementation satisfying most of the problem tvs.

However every chance I get, I remind people who care that you probably want to run the machine on a VGA compatible display. It is only in 50Hz VGA mode that the video timings out of the next will be perfect and will allow timing sensitive demos to display properly. hdmi tvs that support scart can also get vga timing through a scart connector.

The other issue you're mentioning has to do with the expansion bus. Xilinx discontinued 5v tolerant inputs on its fpgas starting with the spartan 6, which is the fpga used in the next. The fpga's interface to the expansion bus is really designed for fpgas with 5v tolerant inputs and really there should be level conversion done on the expansion bus interface instead. Xilinx was switched to from Altera because a good deal was had on their fpgas. I can't say if the Altera part was 5v tolerant but I am guessing it was and no change was made when the Xilinx part was substituted.

What I think is going to happen is a separate thin interface thing that does do level conversion will be recommended to be plugged in for the expansion bus. This is just the way things are - sometimes you have to deal with issues the best way you can. Having said that, legacy devices were based on bipolar ttl which is unable to drive signals higher than what the fpga is tolerant to. This may explain why this method of interfacing has been used on other retro projects for a long time without known ill effects so far.
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Re: ZX Spectrum Next Discussion

Post by Pegaz » Mon May 13, 2019 8:06 am

Alcoholics Anonymous wrote:
Mon May 13, 2019 4:30 am
Bizzley wrote:
Sun May 12, 2019 11:06 pm
It's not just the Right Cursor key that doesn't work reliably, it's quite a few composite key presses that are prone to failure as you can see from the picture and mentioned in the latest Update. They are going to try three different designs for the new contacts and hope that one of them does the job but they won't know if any of them work until they get the results back. That to me sounds more like desperation than having a definite and workable idea of how to fix the problem.
That is exactly what the problem is. It should be made clear that the keyboard is not designed by the next team - it is by a keyboard manufacturer which has plenty of experience building keyboards. They were sure the keyboard would perform well once it was machine assembled rather than hand assembled and they were wrong. Two semi-circle halves as contact means preference for one side or the other in striking leads to one contact being made before the other. If the difference in time is significant this can't be covered up in hardware without affecting the responsiveness of the unshifted key. And that's where it is.

The length of delay is not because there's anything being hidden; it's because the next is a low volume project that has bottom priority for suppliers. They deal with it after higher priority customers are dealt with. Nothing may happen for weeks. Now that they see the machine assembled keyboard does not work as expected, hopefully they have reason to spend some more urgent attention.
Does this mean that Q2 2019 remains as the deadline for delivery?
Who is the manufacturer of these keyboards, anyway?
I guess they have experience in keyboard production and these issues should be solved during testing process, instead of being delayed that much.
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