[vdr] Re: Increasing SDRAM on DVB cards

[Oliver Endriss <o.endriss@gmx.de>]

Hermann Gausterer wrote:
> > Take a look at page 13 of the AV7110 data sheet, which shows its
> > memory map. The SDRAM is at CC000000-CDFFFFFF, while the DRAM is
> > at 2E000000-2FFFFFFF.
>
> ok ok ok, RTFM ;-)
>
> > Well, since SDRAM goes from CC000000-CDFFFFFF and only half of that
> > address space is currently used, your suggestion might work _if_
> > there are actually enough address lines connected.
>
> you can be shure that enough adress lines are connected .. this is
> not an linear adress bus, insteed an multiplexed is used (ROW &
> COLUMN) and we know that the full 2mb are allready accessable (fairly
> yes !!) we know from the specs of the mem chip, that A0-A10 in row
> mode and A0-A7 in colum mode is used.
> that mean, we need an chip that is pin-compatible and uses
> also ROW-A0-A10 and COLLUMN-A0-A8 and the onboard adress
> decoder should JUST SIMPLE WORK (TM) ;-)
>
> > However, since the
> > AV7110 has two explicit SCS lines (SCS1 and SCS2) I would assume
> > that it can handle either one or two 2MB chips, each connected to
> > its very own SCSn line.
>
> yes that could also be true and done, but that would need additional
> handling
> of the memory .. normaly there are programable shadowregister that
> check if an adress is on chip 1 or 2 and sets the PINS automaticaly
> .. or the are using
> another way for hardware or software adressdecoding or even both :-o
> trust me avoid such an aprouch if possible !!!
>
> > But I'm just guessing here... Maybe you're actually on the right
> > track. But then again, what would the SCS2 pin be for?
>
> it would be for an second IC, but my "way" is to use an even greater
> chip that replaces the one on the board

Hm, SCS1 is active for the *first* 2MB block only.
You cannot use SCS1 'as is' for a double-sized SDRAM, because it's only 
active when the lower part of the address space is being accessed.

There are two possible solutions:
- create your own 4MB chip select using the upper address lines
  (don't know whether these lines are accessible)
- re-program SCS1 for a 4MB address block (if I understand the datasheet
  correctly, this is not possible, as the chip selects are fixed)

After all I think that we need SCS2 or it can't be done. :-(

Oliver


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