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Subject: Re: RAM limit
From: Matthias Wächter (matthias_at_waechter.wiz.at)
Date: 2002-08-14


On Mon, 12 Aug 2002, Linus Nielsen Feltzing wrote:

> > I mean, we all know that 2MB is not _that_ much (f.e. for 200+ song
> > titles in the list to sort :-)), other players have 8MB to save
> > battery power (well, to make the device smaller by using smaller
> > batteries). The SH-1 supports up to 16 MB of DRAM, so even if it's
> > a hard and dirty job, one could enhance/replace the memory using
> > additional DRAM modules (f.e. by piggy-packing them on the one
> > already there). An additional address decoder will be necessary,
> > too.
> Then you need another DRAM controller as well, since the DRAM
> controller and address decoder is internal to the SH1.

No.

There are two alternatives:

a) Remove the existing chip (1M x 16) and replace it with a larger chip
(4M x 16). In theory this should work (and by wiring two additional
address lines). In practice, this is nearly impossible for two reasons:
(1) I can't find a manufacturer offering 4M x 16 devices for 5V (maybe I
don't search correctly), (2) I can't find a manufacturer offering any FPM
(fast page mode) DRAM in this size after all (The main age for these chips
was about 1996-1998). Maybe we find some old PS/2-SIMMs we can unsolder
the parts from, but I don't think we will succeed in making something
'easy' and 'for longer times available' to help all Archie-owners
upgrading their devices. Maybe, if the SH1 was a 3.3V component, we
could've found a replacement chip (for 3.3V there are a lot of
manufacturers for 4M x 16 FP-DRAM, maybe one of them has some spare
devices for us), but currently we would need at least 2 x 16bit voltage
translators 3.3V <-> 5V to connect those chips into the Archos. What a
mess would that be! Even if the chip were pin-compatible to the current
1Mx16 chip, we would have to wire all the pin elsewhere.

b) Add additional 1M x 16 chip(s) plus an address decoder. Problem here is
that we get a lot of additional heat (about 0.3 W per memory chip), and
additional heat from the address decoder (about 0.6 W!), which we would
have to put into a GAL. All this not accounting for the additional space
needed for all this. With a clever address decoder design, you can just
use the SH1 with its DRAM controller, though.

For example: While /RAS is asserted (falling edge), the extra address
lines A10,A11 are available to be decoded. One just has to 'gate' the
/CASL and /CASH to the decoded memory chip, the other chips just see a
/RAS access without a /CASx. I already wrote some lines of VHDL code for
the GALs, but I think this leeds us nowhere.

<sigh>

Slowly I think that project is a little bit too much for our little
Archie.

Additional comments? For the chips we would at least need PS/2 SIMMs
with the following features:

a) 16 MB with 2 chips
b) 32 MB with 4 chips (2 chips per side).

the chips should have at least 44 pins each (that would make them 16-bit
chips). Maybe some of us have such SIMM modules in their old dusty
computers...

bye,
- Matthias

-- 
                    "To get control over people, make them trust you.
                                            To make people trust you
                      don't try to tell them the truth about history
                 but make happen what you told them about the future."



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