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 . 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 ?

cheers,
Alex

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.

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.

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 ?

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

umm, lower b means bits thus 512Mb and 1Gb becomes 512/8=64MB and 128MB, mystery solved :-)

Oh, sorry, too late.

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.

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