ARM SoC Embedded Linux

[ACF2802]

Looking to start an embedded Linux project. I know you can find development boards, but I'm wanting to build my own from scratch.

I believe I will be using the AT91SAM9260 (maybe the AT91SAM9XE512) because it seems to be one of the most powerful SoC that is Non-BGA (this is important because this is DIY and BGA components are not friendly at all) that is easily supported by Linux.

I'd like for this board to have a VGA out capable of different SVGA resolutions, but not sure how to go about doing this. Is there a very simple way? Otherwise, I was thinking about putting a Spartan-3E fpga on it that would act like a video controller that outputs to a 8-bit RAMDAC. The Spartan supports DDR memory which could be used as VRAM. My question is what type of performance could I get out of such a configuration? I'd like at least 1024x768x24 @60Hz, but I'd be happy if I could go higher to more modern resolutions.

 

[ACF2802]

I should have also mentioned I would like to have DMA access so the controller can load from main memory without any CPU overhead.

 

[Sceadwian]

Looking to start an embedded Linux project. I know you can find development boards, but I'm wanting to build my own from scratch.

Umm... Why?

 

[ACF2802]

Umm... Why?

Why? Because that's the project! lol. That's like telling someone who wants to build a model airplane to just go out and buy one that's already been assembled and painted.

 

[Ubergeek63]

Looking to start an embedded Linux project. I know you can find development boards, but I'm wanting to build my own from scratch.

I believe I will be using the AT91SAM9260 (maybe the AT91SAM9XE512) because it seems to be one of the most powerful SoC that is Non-BGA (this is important because this is DIY and BGA components are not friendly at all) that is easily supported by Linux.

I'd like for this board to have a VGA out capable of different SVGA resolutions, but not sure how to go about doing this. Is there a very simple way? Otherwise, I was thinking about putting a Spartan-3E fpga on it that would act like a video controller that outputs to a 8-bit RAMDAC. The Spartan supports DDR memory which could be used as VRAM. My question is what type of performance could I get out of such a configuration? I'd like at least 1024x768x24 @60Hz, but I'd be happy if I could go higher to more modern resolutions.

nice... i hope you are not planning on hand soldering wires to that thing. it has 50 pins in an inch! (0.5mm pitch) not to mention that the likelihood of having high speed hand wired busses working right is very small indeed.

dan

 

[ACF2802]

It will be going onto circuit board. I haven't soldered anything quite that big this that many fine pins before, but with the right technique it's not that difficult.

 

[Sceadwian]

ACF. To use the model plane reference, there's a BIG difference between pre-cut kits and having to exacto'ing the whole thing yourself from blue prints on raw balsa stock =) Not that I'm nocking what you want to do, but honestly, there are such nice products no the market already that my first question would be why. Even aside from the hardware complexities you have to write all the software for it as well if it's going to be a fully custom system. Sounds more like a nightmare than a project in my book =)

 

[ACF2802]

ACF. To use the model plane reference, there's a BIG difference between pre-cut kits and having to exacto'ing the whole thing yourself from blue prints on raw balsa stock =) Not that I'm nocking what you want to do, but honestly, there are such nice products no the market already that my first question would be why. Even aside from the hardware complexities you have to write all the software for it as well if it's going to be a fully custom system. Sounds more like a nightmare than a project in my book =)

Not 100% sure what you mean with the balsa stock and exacto knives.

If you are referring to my methods of construction, I'll be using double sided acid etched copper PCB. The traces will be designed with aid of software. I'm not doing this because I want an embedded system. I'm doing this because I want to design and create my own. I thought this was a DIY forum. Ask someone building a hotrod car why they didn't just go out and buy a fully functional car and they would probably look at you as if you were crazy. If I simply wanted to mess with an embedded system, sure, I'd drop the $100-500 on a evaluation board and mess with it to my hearts content.

 

[Sceadwian]

That's fine ACF, as I said, not nocking it if that's what you wanna do =) A lot of people come here asking for that kind of stuff, while what they actually want is the premade stuff.

 

[BeeBop]

Yes, but embedded project have two facets: hardware and software. If I was doing it, I would develop the software on a known good hardware first, then build my own hardware, so I could use the known good software to debug my hardware.
If you just jump in with both at the same time you have more variables to work with...

 

[Ubergeek63]

It will be going onto circuit board. I haven't soldered anything quite that big this that many fine pins before, but with the right technique it's not that difficult.

well that is debatable...

having done so myself, i would say your best bet, assuming you can get it tacked down accurately enough, is to use a fine pitch shovel point with fine solder after swiping the side of the chip with a flux pen. and then have fine pitch wick ready for the inevitable bridges.

dan

 

[Sceadwian]

Or once you get the board design finalized your practice with a paper stencil to lay down a semi-precision band of solder paste and just use a hot air gun to bulk solder the whole thing. If the thickness of the solder paste is carefully controlled (easy enough to do) the solder will naturally wick the leads to the copper pads, the critical bit is using juuuust the right amount of solder paste. And then you can touch up with a fine point soldering iron afterward if required.

 

[DirtyLude]

You know he's not asking about the soldering right? If he says he's done fine pitch before, he's done fine pitch. For some people it's not that hard.

Doing a 9260 on a 2 layer board is going to be kinda tight with all the external RAM.

 

[ACF2802]

I suppose the TI OMAP series of chips would be a good solution because of their built in graphics processor/controller. If I used one of those however, I would need to have a 4 layer PCB manufactured as it is BGA with a high pin count. I've seen plenty of people who have done BGA at home using various methods of reflow.

I've etched simple 1 or 2 sided PCB on copper clad before. Recently I've even seen some people who went as far as to do DIY solder masks and silkscreen on their PCB. One thing I have not seen is anyone who managed to make a multilayer PCB (>2 layers) at home. Anyone here know how difficult it might be? I realize it would be time consuming, but I'm more concerned about the feasibility of it. It would be worth the time and trouble as places online are going to probably charge $200-300. It would be pretty nice for prototyping more complex devices.

 

[DirtyLude]

BatchPCB has a 4 layer option. $8 a square inch for 4 layer plus $10 setup.

 

[ACF2802]

BatchPCB has a 4 layer option. $8 a square inch for 4 layer plus $10 setup.

That's no better. I would be spending $200 for a 4x6" 4-layer PCB. Unfortunately that's not economical for amateur DIY.

 

[DirtyLude]

I'm not certain why you think you need such a large board. You put the chip and SRAM and any other high density items you want on a small 4 layer module and use a larger 2 layer board for peripherals. 4 square inches total would be plenty.

Like these:
AT91SAM9263 (ARM9) CPU Module
MXM-7110 [MXM-7110] : Embedian, Inc., Trusted Embedded ARM/XSCALE Computers
SoM-9307 ARM9 WindowsCE / Linux Single Board Computer Module
**broken link removed**

This thing has to be 6 layer.
**broken link removed**

 

[Ubergeek63]

I'm not certain why you think you need such a large board. You put the chip and SRAM and any other high density items you want on a small 4 layer module and use a larger 2 layer board for peripherals. 4 square inches total would be plenty.

Like these:
AT91SAM9263 (ARM9) CPU Module
MXM-7110 [MXM-7110] : Embedian, Inc., Trusted Embedded ARM/XSCALE Computers
SoM-9307 ARM9 WindowsCE / Linux Single Board Computer Module
**broken link removed**

This thing has to be 6 layer.
**broken link removed**

dunno about that...I regularly do stuff that *should* be 6 layer with parts on both sides of the board on 4 layer single sided mounting.

production is not a problem but it gets weird for rework when you take off a large chip and half it's decoupling caps come with it. production complains but it takes less time to do the extra rework on a few than it does to go through the SMT line twice for each board.

dan