SDRAM board

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Sorgelig
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Re: SDRAM board

Postby Sorgelig » Fri Dec 15, 2017 4:30 pm

Extra small version:
sdram_xs.png

Probably will be tricky to solder. But if it will work not worse than standard vertical module, then is should close the dilemma "which dimension to sacrifice".
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Re: SDRAM board

Postby JimDrew » Fri Dec 15, 2017 4:59 pm

Did you add a 4.7K pull-down to the CKE line in that design?
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Re: SDRAM board

Postby Sorgelig » Fri Dec 15, 2017 5:04 pm

nope. Why?

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Re: SDRAM board

Postby JimDrew » Fri Dec 15, 2017 5:25 pm

To prevent overshoot, and increase the speed of the line going low. Doing this, modules that don't pass at 150MHz always pass at 150Mhz and most pass at 166MHz (vertical design).
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Re: SDRAM board

Postby Sorgelig » Fri Dec 15, 2017 5:42 pm

CKE is always at '1' while working. Some SDRAM modules pull CKE to 1 at power up and never set to 0.

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Re: SDRAM board

Postby ijor » Sat Dec 16, 2017 12:31 am

JimDrew wrote:Did you add a 4.7K pull-down to the CKE line in that design? ...
To prevent overshoot, and increase the speed of the line going low


Are you sure you mean CKE and not something else? Relly it doesn't make much sense on this signal since, as Sorgelig is saying, it is pretty much static.

Note that overshoot can be managed, at some extent, from the FPGA side. The FPGA drivers have programmable drive strength. But this is part of the compilation.

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Re: SDRAM board

Postby alfishe » Sat Dec 16, 2017 3:39 am

ijor wrote:Note that overshoot can be managed, at some extent, from the FPGA side. The FPGA drivers have programmable drive strength. But this is part of the compilation.


I've did an experiment when the whole FPGA bank switched to 2.5V instead of 3.3V and with Alliance SDRAM chip it gave few additional MHz of frequency. Probably playing with various types of termination might give even more.

But it didn't work with all other chips (ISSI, Micron). They draw 2-3 times more current per line (as per datasheets)

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Re: SDRAM board

Postby JimDrew » Sat Dec 16, 2017 5:35 am

The SDRAM is always high once the board is powered up? Maybe there is some type of impedance issue that is resolved with a 4.7K resistor to ground on CKE (pin 37)? This was something that Mike mentioned that Replay hardware does (and it does according to the schematic), so I decided to try it.
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Re: SDRAM board

Postby ijor » Sat Dec 16, 2017 3:35 pm

alfishe wrote:I've did an experiment when the whole FPGA bank switched to 2.5V instead of 3.3V and with Alliance SDRAM chip it gave few additional MHz of frequency ...


Interesting, but I wasn't talking exactly about the voltage levels. The FPGA supports programmable slew rate and output current strength that can be set individually on each output pin. There is even programmable on chip termination.

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Re: SDRAM board

Postby olin » Sat Dec 16, 2017 6:36 pm

Sorgelig wrote:Probably will be tricky to solder.

Then maybe try something like this:

sdram_vert_mount.jpg

Illustrative image how to mount vertical SDRAM board on the dual row header pins.

The board of 1.6mm thickness fits nicely in between the dual row header pins, which can be soldered to pads on the SDRAM board. You still achieve 'non-bending' connection to some of the traces (one side will have to use vias to reach the chip though) and compact size.
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Re: SDRAM board

Postby Sorgelig » Sun Dec 17, 2017 4:36 am

olin wrote:
Sorgelig wrote:Probably will be tricky to solder.

Then maybe try something like this:

sdram_vert_mount.jpg
Illustrative image how to mount vertical SDRAM board on the dual row header pins.

The board of 1.6mm thickness fits nicely in between the dual row header pins, which can be soldered to pads on the SDRAM board. You still achieve 'non-bending' connection to some of the traces (one side will have to use vias to reach the chip though) and compact size.

Tricky doesn't mean impossible. And for me it's not a problem. It will be tricky for mass production as it will require pre-cut pins. For mass production i will keep traditional v3.x version. I've made a slightly slimmer v3.3 (not published yet).

Your suggestion won't produce as slim as i did. It also will introduce other problems. It won't be solid and may tear off the traces while inserting or removing the board. Since chip uses surface pads, it will require additional holes for half traces and most likely will end with extra space between chip and connector. I was thinking about this connection at earlier development stages and found it less useful as current one.

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Re: SDRAM board

Postby JimDrew » Sun Dec 17, 2017 6:45 am

I can mass produce the super slim version. I have a machine for trimming connector pins. I am just about sold out of the original version.
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Re: SDRAM board

Postby Sorgelig » Sun Dec 17, 2017 7:18 am

JimDrew wrote:I can mass produce the super slim version. I have a machine for trimming connector pins. I am just about sold out of the original version.

Good!
But don't rush. I didn't get PCB yet, so i didn't test it.

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Re: SDRAM board

Postby olin » Sun Dec 17, 2017 7:24 pm

Sorgelig wrote:I was thinking about this connection at earlier development stages and found it less useful as current one.

Fair enough.

I was wondering what is the second thinner board connected quite close to your SDRAM board as seen on many of your snapshots? Is it some sort of heat spreader made of PCB with exposed copper layer attached to the SDRAM IC? I didn't find it mentioned anywhere (maybe I overlooked something).

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Re: SDRAM board

Postby Sorgelig » Sun Dec 17, 2017 8:43 pm

May be RTC board which is connected to LTC port?

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Re: SDRAM board

Postby olin » Sun Dec 17, 2017 9:39 pm

I don't think it's RTC. I mean this:
sdram_dual_board.jpg

There are 2 identical size SDRAM boards close to each other... That's why I thought it's a heat -spreader... but probably it is not. What is it then (or what it was then if it is no longer used)? Sorry, just curious :)
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Re: SDRAM board

Postby Sorgelig » Sun Dec 17, 2017 10:58 pm

Ah, this is simple shield/cover. Originally it was supposed to reduce EMI to SDRAM, but turned out useless. Although it makes SDRAM look more like module than bare board.

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Re: SDRAM board

Postby Sorgelig » Thu Dec 21, 2017 5:21 am

This is how extra slim SDRAM board looks like:
20171221_130253.jpg

20171221_130330.jpg

20171221_130142.jpg


here is how connector should be soldered to allow SDRAM chip overlay smoothly:
20171221_105333.jpg


Performance of this module is the same as standard vertical SDRAM. Passes 150MHz. Has few errors on 167MHz.
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Re: SDRAM board

Postby Sorgelig » Thu Dec 21, 2017 8:05 am

Extra slim SDRAM board has been released.
Note: it uses 6 capacitors (instead of 5) due to placements. Probably 5 caps could be enough and the middle one in group of 3 can be omitted, but i suggest to solder all caps.
SDRAM_uni design will coexist with new extra slim version since the later one requires non-standard soldering procedure.

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Re: SDRAM board

Postby Sorgelig » Thu Dec 21, 2017 1:57 pm

Wiki page about SDRAM DIY has been updated as well: https://github.com/MiSTer-devel/Main_MiSTer/wiki/SDRAM-Board-Assembly-(DIY)

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SDRAM Board Problem

Postby cavemanxzx » Sat Dec 30, 2017 11:25 am

Hi,

i have here a SDRAM Board that is not working with any core, but running for hours through memtest 150 Mhz and also lower without any Errors. 167 Mhz give errors from start.


I think my Board is Thrash, but is memtest working correct?

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Re: SDRAM Board Problem

Postby Sorgelig » Sat Dec 30, 2017 1:29 pm

cavemanxzx wrote:Hi,

i have here a SDRAM Board that is not working with any core, but running for hours through memtest 150 Mhz and also lower without any Errors. 167 Mhz give errors from start.


I think my Board is Thrash, but is memtest working correct?

What you see in cores? What makes you think it doesn't work?

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Re: SDRAM board

Postby cavemanxzx » Sat Dec 30, 2017 2:12 pm

First to say I have second Board that works correct.

Minimig with Kick 1.3. You get the Rom init dark grey, light grey and then white, but no prompt for Disk.
NES no games running.
X68K hangs on init (Vertikal lines)

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Re: SDRAM board

Postby Sorgelig » Sat Dec 30, 2017 2:34 pm

if memtest is passed on 150MHz, then other cores should work.
Probably memtest misses some problems such as broken RAM cell of shorted lines (by solder bridges).
It's hard to say where is the problem.. Did you solder it by yourself?
Try ZX core - what behavior you will see?

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Re: SDRAM board

Postby cavemanxzx » Sat Dec 30, 2017 3:44 pm

I think the Ramchip is bad.

Soldered by myself. No shortcuts.

ZX: black Screen on startup. when injecting a TAP some graphic corruptions.


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