SDRAM Reliability

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lamarax
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Re: SDRAM Reliability

Unread post by lamarax »

As long as JT is willing, or capable, to put his observations into silicone, I'm betting people would flock to buy the new and improved modules.
silentheaven83
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Re: SDRAM Reliability

Unread post by silentheaven83 »

lamarax wrote: Sun Dec 27, 2020 9:36 pm

As long as JT is willing, or capable, to put his observations into silicone, I'm betting people would flock to buy the new and improved modules.

Frankly I wouldn’t, I bought in September a 128 MB board from https://misterfpga.co.uk that fails in SFZero CPS 1.5 and I bought it to be future proof, and it wasn’t really cheap as I live in Italy.

I hope Jotego can do what Sorg says, to find a workaround and use everything we already have.

silentheaven83
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Re: SDRAM Reliability

Unread post by silentheaven83 »

Sorg thank you for your input.
Sorgelig wrote: Sun Dec 27, 2020 5:49 pm Also, with existing CPS1.5 core we have an additional test for memory, so sellers will test their modules on this core before ship. Still there can be a very small amount of modules passed on seller's test platform which will fail on user, but it will be very small fraction. Reputable seller will replace it.
The problem would still remain for the people like me who already bought 128 MB v2.5 boards that fail this test. I don’t know if sellers would accept the returning boards, fix them and ship again to the customers.

If you sell 2.5v boards that can fail the test and then you start selling the same version but only if it doesn’t fail the same test I think it’s not fair for first buyers. I’m talking about reputable sellers of course.
PikWik
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Re: SDRAM Reliability

Unread post by PikWik »

im hoping that moving forward, SDRAM sellers run an additional more extensive memory test and also disclose the specific capacitors (ex. kemet) they use for their modules.
if sorg or someone else can create a more thorough memory test for sellers to use, this will also create peace of mind for first time buyers.

and i actually do think sellers will be willing to fix memory modules that give errors with current cores.
(if bought within a certain amount of time, seller approved repair, or small fee to pay for shipping)
this kind of service will only help give the seller a better name and respect from the MiSTer community.
Lodovik
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Re: SDRAM Reliability

Unread post by Lodovik »

Thanks Jotego for exposing the limits of the current design and coming with suggestions for improving on it.
optyfr
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Re: SDRAM Reliability

Unread post by optyfr »

Don't worry, JT will find a solution to make CPS 1.5 to work with most of current SDRAM modules, but maybe a very little % of users will still get troubles with it (but those should also fail probably with the official memory test). Although, take it more as a warning for future cores that will require more and more BW with SDRAM...
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Alkadian
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Re: SDRAM Reliability

Unread post by Alkadian »

Alkadian wrote: Sat Dec 26, 2020 10:58 pm First of all thank you so much Jotego for your very much appreciated hard work!

Well, I am also one of the lucky ones with no ram issues at all apart from Slammasters which it won't boot. Infact I have got two mister setups with two 128mb ram modules. So I consider myself double lucky :mrgreen:

Anyways regarding the PSU query I have got mine which is a Mean Well unit rated @ 5v, 4A, 20W and again no issues so far...touch wood :D
Thanks Jotego! With the latest telease of the core, Slammasters runs perfectly fine! :mrgreen:

EDIT: I have spoken too early, after the first stage I have got illegal instructions error messages, but at least now it boots up! :D
MostroW
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Re: SDRAM Reliability

Unread post by MostroW »

That's kind of a hard demand of someone who puts in his personal time?
If Jotego (or any other author for that matter) had any interest of sharing his / her work then they would've made it public.

Also i think he has made a lot of his work opensource, just check his signature for his git.


EDIT:
Did someone just remove his post or did he remove that himself?
galibert
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Re: SDRAM Reliability

Unread post by galibert »

Sorgelig wrote: Sun Dec 27, 2020 6:00 pm Aside from SDRAM...
I was wondering, why sdram? synchronous static ram would give you an access every cycle, it seems (pipelined), and memory bandwidth on random access is a real problem, especially for arcade...

OG.
MadDog
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Re: SDRAM Reliability

Unread post by MadDog »

jotego wrote: Fri Dec 25, 2020 5:22 pm
lamarax wrote: Fri Dec 25, 2020 4:31 pm I still have to ask though; what happened with the Street Fighter (Capcom 68000) core, and why this doesn't boot for anyone after having been updated to run @ 48Mhz, a measure taken to supposedly bypass the objective problems that you're describing re: existing 128MB modules?
I was in a rush and uploaded the wrong file. Apologies about that.
Ah. Glad I looked for a post about this... I didn't see a bug reported on the jtsf core about Street Fighter not booting after the latest update. Please don't feel rushed - I'm just glad it's not just me and Jotego is aware. Fantastic work. Take your time, and thank you (and literally every other core developer) for the nostalgia!! :D
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jdeberhart
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Re: SDRAM Reliability

Unread post by jdeberhart »

galibert wrote: Sun Jan 03, 2021 9:45 pm
Sorgelig wrote: Sun Dec 27, 2020 6:00 pm Aside from SDRAM...
I was wondering, why sdram? synchronous static ram would give you an access every cycle, it seems (pipelined), and memory bandwidth on random access is a real problem, especially for arcade...

OG.
Because SRAM is stupidly expensive for anything more than a few hundred kilobytes. You'd easily be looking at $500+ USD for a 128 MB SRAM module.
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jotego
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Re: SDRAM Reliability

Unread post by jotego »

I received a couple of weeks ago some SDRAM boards using the v2.9 design. This version uses a voltage regulator and has other improvements to prevent some of the issues discussed above. I have not found problems so far and measuring the memory supply voltage, is most of the time around 3.3V, with occasional peaking at ~3.7V and 2.8V. Remember that we were seeing peaks at 4.04V (max) and 2.38V (min) before and that the specification is 3.3±10%. So the voltage ripple is much better now and should not be a problem.

Although I have used several boards, I have only measured one. The voltage seen is across the capacitor besides device U4 (the voltage regulator).

Thanks to Nathan from MiSTer FPGA UK for the samples.
SDRAM v2.9 VDD-VSS.png
SDRAM v2.9 VDD-VSS.png (35.45 KiB) Viewed 4249 times
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