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Re: Adding RAM to Pi

Posted: Wed Aug 20, 2014 9:26 pm
by Joe Schmoe
fruitoftheloom wrote:1GB PoP Memory is certainly feasible, but no one manufactures them and considering that the likely market for them is small the price would be prohibitive !
The point of my analogy was that it is not the memory that is the limiting factor. It is the 2835 CPU.

Isn't 512M the max memory of the 2835 - based on the number of address lines it has?

Re: Adding RAM to Pi

Posted: Wed Aug 20, 2014 9:37 pm
by pluggy
Joe Schmoe wrote:Note that this question is basically equivalent to:
Can I add more than 1M of memory to my 8086 PC?
(Yes, I know that the real maximum is 640K, but it can address up to 1M)

(And yes, I am ignoring so-called "expanded" memory)
Don't take us back to the bad old days of fudged memory addressing. I'm presently working on a pretty ancient laptop whose BIOS reports its 1GB of ram as being Expanded memory and its 'real' memory as only 640k. I haven't seen that in a long time.

Re: Adding RAM to Pi

Posted: Wed Aug 20, 2014 9:55 pm
by plugwash
Joe Schmoe wrote: Isn't 512M the max memory of the 2835 - based on the number of address lines it has?
AIUI from previous posts by gert it has the ability to address 1 gigabyte but it only has an 8-bit wide bus and one chip select and noone makes a 1 gigabyte (8 gigabit) LPDDR2 chip in that configuration.

Higher end devices have wider busses and/or multiple chip selects alllowing multi-die packages to be used.

Re: Adding RAM to Pi

Posted: Wed Aug 20, 2014 10:09 pm
by fruitoftheloom
plugwash wrote:
Joe Schmoe wrote: Isn't 512M the max memory of the 2835 - based on the number of address lines it has?
AIUI from previous posts by gert it has the ability to address 1 gigabyte but it only has an 8-bit wide bus and one chip select and noone makes a 1 gigabyte (8 gigabit) LPDDR2 chip in that configuration.

Higher end devices have wider busses and/or multiple chip selects alllowing multi-die packages to be used.
http://www.raspberrypi.org/forums/viewt ... 64#p600904

Re: Adding RAM to Pi

Posted: Wed Aug 20, 2014 10:25 pm
by DirkS
pluggy wrote:Don't take us back to the bad old days of fudged memory addressing. I'm presently working on a pretty ancient laptop whose BIOS reports its 1GB of ram as being Expanded memory and its 'real' memory as only 640k. I haven't seen that in a long time.
Ah... that reminds me of my home made floppy copy program (written in Turbo Pascal and assembler) that could use expanded mem, extended mem, and even my 30MB HDD for intermediate storage to copy 1.44MB floppies in 1 go... happy days :lol:

Re: Adding RAM to Pi

Posted: Wed Aug 20, 2014 10:44 pm
by pluggy
A whole 30 MB ?, my first hard drive was only 20....

The memory in a Pi would swallow the whole hard drive 25 times over. Things have moved on in the 27 years since I bought my first hard disk. :)

Re: Adding RAM to Pi

Posted: Wed Aug 20, 2014 11:02 pm
by mahjongg
curious minds want to know....

has anyone read http://www.raspberrypi.org/documentatio ... herals.pdf (the BCM2835 ARM Peripherals document)?

Does anybody know what the "secondary memory interface" is that is mentioned on page 103, as an alternative GPIO use?

Wikipedia describes "secondary memory" as memory, ( https://en.wikipedia.org/wiki/Secondary_memory ) ... that is used to store a large amount of data at lesser cost per byte than primary memory. examples are hard disks and such.
The point is that the GPIO's seem capable to be used as a simple parallel memory interface using the ALT1 alternative GPIO function. Perhaps this can now work, now that the B+ has more GPIO's.

is this one of the best kept PI secrets, that it can support a fast swap memory system?

Can we indeed implement a super fast swap file mechanism using this interface, or am I imagining things?

Re: Adding RAM to Pi

Posted: Wed Aug 20, 2014 11:40 pm
by ci.v.ic
I also would be really interested in informations about this memory interface for a project at our university. I'm searching for months but nobody can help me, e.g. Broadcom even does not answer.

However, this is the most strange memory interface I've ever saw, with more data than address lines. I hope that this is only a bug in the doc, otherwise I don't know how I could use it.

Re: Adding RAM to Pi

Posted: Wed Aug 20, 2014 11:57 pm
by jehamann
so do you guys have any suggestion on how I would go about building my own single bored computer. I know I can buy one more powerfull but I would like to build one. I plan on trying to build a simple computer like something from the 80s but I eventually want to move on to something more powerful then the raspberry pi.

Re: Adding RAM to Pi

Posted: Wed Aug 20, 2014 11:59 pm
by DirkS
single bored computer
:shock:

Re: Adding RAM to Pi

Posted: Thu Aug 21, 2014 12:23 am
by mahjongg
ci.v.ic wrote:I also would be really interested in informations about this memory interface for a project at our university. I'm searching for months but nobody can help me, e.g. Broadcom even does not answer.

However, this is the most strange memory interface I've ever saw, with more data than address lines. I hope that this is only a bug in the doc, otherwise I don't know how I could use it.
wondered about that too, but it could be implemented as something like a FIFO with the addresses addressing registers with which you can choose which block (of say 512 words) to address and such. The peripherals document is really stripped (I assume) of the relevant data, but I assume what is meant is a "block device", instead of a "random access device". In fact a very fast block device would be ideal for a swap file (virtual memory) mechanism.
But that is just my two cents worth of interpretation, a bit inspired on how the parallax propeller handles external RAM.

its getting "curiouser and curiouser" :mrgreen:

Re: Adding RAM to Pi

Posted: Thu Aug 21, 2014 12:32 am
by plugwash
fruitoftheloom wrote:1GB PoP Memory is certainly feasible, but no one manufactures them and considering that the likely market for them is small the price would be prohibitive !
1GB and even 2GB PoP memories exist, they just have wider bus width and/or more than one chip select line so they aren't compatible with the processor on the Pi.

Re: Adding RAM to Pi

Posted: Thu Aug 21, 2014 4:39 am
by Jessie
This month after 2 years I finally hit a RAM wall with EmulationStation 2.0. So there is indeed an app that will take all it can get. There are users with large libraries reporting that 320MB is the minimum amount to allocate to the GPU. It is well written with all vector graphics and looks nice but it loves plenty of vram. My config requires 256MB to keep from getting artifacts.

I would think that after almost 3M units sold (maybe more) someone would be willing to create a 768MB or 1G POP chip for the Pi. I admit that those of us filling the 512MB are few and far between but that doesn't mean that it makes us want more any less.

Re: Adding RAM to Pi

Posted: Thu Aug 21, 2014 6:52 am
by fruitoftheloom
plugwash wrote:
fruitoftheloom wrote:1GB PoP Memory is certainly feasible, but no one manufactures them and considering that the likely market for them is small the price would be prohibitive !
1GB and even 2GB PoP memories exist, they just have wider bus width and/or more than one chip select line so they aren't compatible with the processor on the Pi.
WHATEVER

Re: Adding RAM to Pi

Posted: Thu Aug 21, 2014 7:27 am
by RaTTuS
Jessie wrote:...
I would think that after almost 3M units sold (maybe more) someone would be willing to create a 768MB or 1G POP chip for the Pi. I admit that those of us filling the 512MB are few and far between but that doesn't mean that it makes us want more any less.
that's the problem - there is no upgrade path so you cannot get those 3M units back you have to sell new ones
and if you where making those POP modules it is a very closed circle of things it can go on....
my bet that in 2years [whatever] when a new RPi comes out it will have more RAM - but not for the original RPI .... ;)

Re: Adding RAM to Pi

Posted: Thu Aug 21, 2014 8:28 am
by pluggy
The Broadcom engineers who who post on here have said several times the SOC won't do more than 512MB. It makes sense since the SOC was never envisaged to be used as a computer. Its a smart telly chip - a powerful GPU with a very small (old) ARM processor shoehorned onto the die. No doubt the next version of the the Pi with a different SOC will have more RAM.

Re: Adding RAM to Pi

Posted: Thu Aug 21, 2014 8:57 am
by rpdom
They actually said that it will address 1GB/8Gb maximum, but (as already mentioned) no one makes 8Gb POP RAM with only one select line. The existing chips are all 2x4Gb on a single chunk of sand with a select line for each half of the chip.

I guess it wouldn't be hard for those chip makers to design a compatible chip, but the cost of setting up would outweigh any income generated from a possible couple of million or so sold for a single product that might well be superseded in a few years time.

Re: Adding RAM to Pi

Posted: Thu Aug 21, 2014 9:02 am
by gregeric
Not so pluggy, as rpdom says: 1GiB is the physical limit for the POP memory, but practically limited to 512MiB cos no-one has manufactured a compatible chip. From the rather hoarse Broadcom Eng's mod's mouth: http://www.raspberrypi.org/forums/viewt ... op#p222583

Re: Adding RAM to Pi

Posted: Thu Aug 21, 2014 9:13 am
by pluggy
I stand corrected. So any volunteers to make a compatible memory modules ?, VERY deep pockets a distinct advantage.....

Re: Adding RAM to Pi

Posted: Thu Aug 21, 2014 9:52 am
by plugwash
jehamann wrote:so do you guys have any suggestion on how I would go about building my own single bored computer. I know I can buy one more powerfull but I would like to build one. I plan on trying to build a simple computer like something from the 80s but I eventually want to move on to something more powerful then the raspberry pi.
How much time and money do you have?

First there is the design, back in the old days when clock speeds were low and noone cared about EMC laying out boards was just a matter of laying out tracks to match a scematic. Nowadays that's no longer the case, layouts have to manage high speed signals where the behaviour of PCB tracks is far from the concempt of an ideal wire, very high signal densities and a need to keep lines from power pins to the decoupling caps very short. Honestly lots of board designers just copy the SoC vendors reference design for the critical bit arround the SoC

Then there is the board manufacture, you are talking multilayer boards, often with blind vias and with very small feature sizes. That doesn't come cheap in low volume.

Then there is the assembly, if you want to do this yourself you need microscopes, placement tools etc if you want to contract it out expect to pay, especially if the SoC you choose uses PoP

If you are really interested in this stuff I belive the design files for the beaglebone black are available and would be worth looking at to get an idea of what is involved.

Re: Adding RAM to Pi

Posted: Thu Aug 21, 2014 10:36 am
by ame
jehamann wrote:so do you guys have any suggestion on how I would go about building my own single bored computer. I know I can buy one more powerfull but I would like to build one. I plan on trying to build a simple computer like something from the 80s but I eventually want to move on to something more powerful then the raspberry pi.
Here you go:
http://hackaday.com/2014/08/19/the-most ... -computer/

Unmarried, bored computer.

Re: Adding RAM to Pi

Posted: Thu Aug 21, 2014 10:48 am
by Gert van Loo
A real engineer will always come up with a solution.
That is why you do not want an engineer freely talking to customers and
always place a marketing person next to him to restrain him.

So here is the UN-restrained engineer talking.
To get more memory on a Pi you have to develop a PoP chip which has multiple memory chips on it plus a small MMU.
The MMU will allow you to map different areas of the various memory chips onto the 512M memory map as can be seen by
the processor. You also have to carve out a small part of the 512M memory map to access and control the MMU.

This way there is no technical limit to the amount of memory you can connect.

Re: Adding RAM to Pi

Posted: Thu Aug 21, 2014 10:56 am
by ame
Gert van Loo wrote:A real engineer will always come up with a solution.
That is why you do not want an engineer freely talking to customers and
always place a marketing person next to him to restrain him.
You are being ironic, I hope.

In my experience you do not want marketing talking to customers as they will invent features that we don't have, and sell them. Then we engineers have to implement whatever brain-dead ass-hattery they came up with.

Re: Adding RAM to Pi

Posted: Thu Aug 21, 2014 10:57 am
by DirkS
Gert van Loo wrote:A real engineer will always come up with a solution.
That is why you do not want an engineer freely talking to customers and
always place a marketing person next to him to restrain him.
Hmmmm... https://www.youtube.com/watch?v=BKorP55Aqvg

Re: Adding RAM to Pi

Posted: Thu Aug 21, 2014 11:12 am
by toxibunny
RASPBERRY PI FOUNDATION ENGINEER LEAKS DETAILS OF 'NO LIMIT' RAM UPGRADE.