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Re: DRAM on USB

Posted: Tue Nov 01, 2011 10:04 pm
by matt_heys
Ok, odd question I know but has anyone ever seen a product that has DRAM on USB, or any type of high speed memory that doesn\'t have finite write cycles that NAND has?

I\'m thinking about a small USB Swap partition, high IO but without wearing out quickly, doesn\'t need to be persistent either.

Some company did an enclosure that had DDR sockets in it and a SATA interface but it was big, ugly and expensive (with no ram in!).

256mb would probably do, so that\'s 1x128mb dram on either side of the pcb. That should be fairly small.

Re: DRAM on USB

Posted: Wed Nov 02, 2011 10:08 am
by colbhaidh
Should be quite straight forward to build one using the PIC18F microcontroller although the speed would be limited to 12Mb/sec for consecutive reads or writes.

Re: DRAM on USB

Posted: Sat Nov 05, 2011 11:48 am
by theomarkettos
An FPGA board with sufficient DRAM should do, but you\'d have to design the USB-DRAM interface. AFAIK there\'s no standard protocol for using DRAM over USB. I suppose you might want it to look like a mass storage device, but don\'t forget you\'d have to \'format\' it every time you power on.

Or you could take a USB flash controller, and just use convert the flash output to drive a DRAM - might be more manageable, but would still need an FPGA.

Re: DRAM on USB

Posted: Sat Nov 05, 2011 12:57 pm
by obarthelemy
easier: buy a SATA ramdisk, and put it in a USB enclosure. http://techreport.com/articles.x/16255 ; http://en.wikipedia.org/wiki/I-RAM
drawback: you could buy several tens, or hundreds, of Pi for the same price.
conclusion: not worth it. Exercise software/OS ingenuity to deal with constraint, and leave wallet / soldering iron at rest.

Re: DRAM on USB

Posted: Sat Nov 05, 2011 8:07 pm
by portets
[quote]Quote from colbhaidh on November 2, 2011, 10:08
Should be quite straight forward to build one using the PIC18F microcontroller although the speed would be limited to 12Mb/sec for consecutive reads or writes.[/quote]

i really hope a project like this really takes off for the pi. i love hardware hacking.

side-note: could ram be added through the gpio ports?

Re: DRAM on USB

Posted: Sat Nov 05, 2011 9:29 pm
by Bacan
[quote]Quote from portets on November 5, 2011, 20:07
side-note: could ram be added through the gpio ports?[/quote]

I thought of that idea, then discounted doing it because of the lack of address/data lines available in the GPIO. But I\'m just a Business/Firmware/Software guy.

Re: DRAM on USB

Posted: Mon Nov 07, 2011 2:26 pm
by Huulivoide
Just buy some cheap external usb HDD,
and create a swap partition on it, you also
gett \'LOTS\' of storage space. :D

Re: DRAM on USB

Posted: Tue Nov 08, 2011 9:03 pm
by caminati
Oddly, the same topic emerged on tinycore forum some time ago:
http://forum.tinycorelinux.net/index.php?topic=9550.15

More recently, I was planning to simply use the sd card to swap; they are just cheap: 5 euros (even less) for 2 gb.
That would be slow, but not much slower than the bottleneck imposed by usb2, and things would vary depending on the SD class (by the way, that of SD classes is a tiering system I find ambiguous).
I estimate that months have to pass before the first wearings, then you buy another one.
By putting the OS on a partition and the swap on another, one should have an easy time in transfering the first on the new SD.

Re: DRAM on USB

Posted: Tue Nov 08, 2011 11:15 pm
by theomarkettos
I use a USB flash stick as swap in my router (32MB RAM, MIPS 233MHz CPU). The performance of the router matters a lot depending on the speed of the flash stick - it\'s not the read/write time that matters, it\'s the latency. A stick with ReadyBoost support made a big difference - this means latency is less than 1ms. In 5 years I\'ve got through 3 USB sticks (replacing as a precautionary measure).

For the same reason, RPi speed in Linux depends a lot on the SD card speed if used as swap. With a slow card, the machine is noticeably slower to respond. So a fast USB stick will probably be a substantial improvement. USB SSD will be better, and USB DRAM (if such existed) will be better still.

Re: DRAM on USB

Posted: Tue Nov 08, 2011 11:34 pm
by RobertM
You can buy USB drives with DRAM caches too