770 RAM expansion

[ddalex]

Hello,

I got last weekend the repair schematics for the 770 and N800. I have a 770 and I'd like to increase the RAM so I can run bigger apps and decrease the load on the swap file :), with better performances.

The idea was to take out the combo memory chip and replace it with something with bigger size. But I was surprised to see that the combo chip is marked as 512Mb DDR + 1Gb NAND, and that only 64Mb RAM and 128 Mb NAND are used... what a waste !. So I'm trying to figure out how to mod the 770 (warranty already expired) to put the rest to the use.

So I'm taking a look at the repair schematics, page 7 out of 11. Here the OMAP chip is shown directly linked to the memory, and if I remember correctly, the OMAP includes the memory controller - this makes sense. I'm focusing on SDRAM part, and we have this signals:
- SDRAM_AD(0:15) with 12 lines connected on memory chip and 13 lines connected on OMAP ????; this makes between 14 and 16 lines for addressing,
addressing 16K to 64K of memory
- SDRAM_BA(0:1) with 2 lines of memory bank selection !?!?
- SDRAM_CTRL(0:9) with 10 lines for control, labeled clearly enough
- SDRAM_DA(0:1%) with 16 lines of data

The Combo memory has quite a few of Not Connected pins, and the Omap processor has 16 NC pins labeled ExtAdDa, and 9 more NC pins labeled ExtDa.

This tells me that the OMAP 1710 (presumably pictured in schematics) can transfer data on 32 bits (SDRAM_DA w/ ExtAdDa) and for 41 bits addresses (SDRAM_AD w/ ExtAdDa w/ ExtAd), up to 2 Terabytes !. However if we're limiting to SDRAM_AD and ExtAdDa we still get a whopping addressable 2G RAM, which should pose no problem addressing the 512 Mb supposedly available on chip.

Back to seeing possible addressing modes:
14-16 lines of address -> 16 K to 64 K of memory addressed by directly sending the address
2 lines for bank selection -> 64 K to 256 K accessed with bank selection
2 bytes transfered at once -> 16 bit memory granularity -> 128Kb to 512Kb of 16-bit memory addressed by direct addressing w/ bank selection
So there still are a couple of lines to figure out till the 64Mb limit - this means a composite memory addressing mode.

So I have a couple of questions, if anyone here can help me I would be grateful:
- does anybody have detailed specs of the OMAP and memory Combo chips ? :)
- what is the current addressing mode used ? I hope that by modifying the current addressing mode, I could get the RAM increase without soldering :D. Anyway for this point I'm gonna start up and read the kernel :)
- someone with the right tools, can pls trace what signals pass between the OMAP and the memory chip ? :D

cheers,
Alex

[TA-t3]

The idea was to take out the combo memory chip and replace it with something with bigger size. But I was surprised to see that the combo chip is marked as 512Mb DDR + 1Gb NAND, and that only 64Mb RAM and 128 Mb NAND are used... what a waste !.
I'm not familiar with the chip in question. But if it's really marked with 512Mb/1Gb (or 1024Gb) then my guess is that it's really Mb and Gb, not MB and GB. In other words, bits, not bytes. It's quite a common way to mark memory chips after all. 512Mb/1024Mb corresponds to 64MB/128MB, which is exactly what the 770 has for RAM/Flash.

[choffee]

Are you sure it's 512 MegaBytes I think that RAM is often sold in Bits so 512 MegaBits would give you 64 Mega Bytes.

[ddalex]

Valid point taken :)

In this case, it's possible to replace said chip with something similar but with higher capacity. Still the problem of the addressing mode used remains...

Anyone help ?

[kosmic]

I don't known, the combo memory chip look like a BGA or QFN package (pin under the chip)... you will have a hard time solder a new one on the board.

Kos

[fanoush]

But I was surprised to see that the combo chip is marked as 512Mb DDR + 1Gb NAND, and that only 64Mb RAM and 128 Mb NAND are used... what a waste !
umm, lower b means bits thus 512Mb and 1Gb becomes 512/8=64MB and 128MB, mystery solved :-)

Oh, sorry, too late.

[bartsimpson123844]

How much more RAM can you fit in the 770's case? That would be sweet if you could double it, it would be capable of much more.

[TA-t3]

Nothing has surfaced so far to indicate that the RAM can be extended in any way whatsoever.