13 Dec
2013
13 Dec
'13
10:29 a.m.
Wow, this is old but got stuck in my drafts box. Thought I'd send it
now; still willing to work on this sort of thing, but I have massive
time constraints for the next few months.
On Aug 13, 2013, at 14:26, Andrew Lynch <lynchaj at yahoo.com> wrote:
Hi Ryan! Thanks! We need help with a dense, fast
DRAM/SDRAM/DDRx board in the worst way. Phat stacks of DDR RAM in the GBs and that
requires DDR encoder/decoder logic.
Neither John nor I know anything about it other than it is quite complex. I've used
the old school DRAMs (4164) but they are nothing in comparison to DDRx or whatever its
called.
Help! This is an urgent appeal. The S-100 80386 CPU board is basically boned without a
decent RAM board to go along with it. We have an 8MB SRAM board that works and can design
an 32MB SRAM board but that just gets you in the door.
Sophisticated Linux/BSD OS's all require GBs of RAM and 32MB won't even get a
boot screen. Maybe a dirty look from the barest of the bare bones Linux distributions.
Not much else.
I'm glad to help (I do this professionally), but I'm out of town for
the next two weeks. Ping me after that, though; you should be able to
at least do some standard 3.3v SDRAM (not DDR) with a small CPLD. You
can do DDR 1/2/3 with small, low-cost FPGAs. All of this will require
surface mount (neither RAM nor FPGAs come in anything else now), but
you could at least use SODIMMs to avoid most work with BGAs.
I can't do the pin math in my head to think if you could use QFP
packages for the FPGA, but I suspect not; this may be something that
would be worth doing at an assembly house, even if just for the SMD
components. You're not going to get away without using surface-mount
bypass caps for an FPGA, either.
Long story short, if you can deal with the space provided by standard
SDRAM, it's probably your best bet.
Let me know how I can help. I'm glad to help with schematic and layout
in my spare time. Don't even THINK of touching SDRAM layouts with an
autorouter. It will not save you any time or effort, because you will
spend more time cleaning up after it than it would have taken to hand
route it to begin with.
- Dave