SDRAM Reliability

[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...

[Alkadian]

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

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

Thanks Jotego! With the latest telease of the core, Slammasters runs perfectly fine!

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

[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]

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]

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!!

[jdeberhart]

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.

[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 (35.45 KiB) Viewed 5020 times