# Beginning arm cortex Ax hardware development

Where can one find information on how to put together a minimal linux bootable board based on the cortex A family (like the beagleboard)? Programming information is plentyfull, but hardware knowledge appear more arcane. I'm especially curious about:

• What external components are needed and why.
• Why dev boards seems to end up around 200$, even though I could get an omap3517 for 15$?
• What kind of equipment is needed to create prototypes around a chip such as the omap3517?
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I've been blogging about the Linux board I've been working on starting here and continuing here. I started thinking I would use a Cortex A8, but eventually settled on the Atmel AT91SAM9G20.

• You can see the components I used in my schematic, but I don't know of a more general explanation of why each is necessary.
• The processor is only about 10-20% of the total cost of parts. Assembly is another $4-40, depending on the quantity built. I suspect the profit margin is 30-50%. • Depending on the package, the OMAP3517 BGA package has either a 1 mm or 0.65 mm ball pitch. Generally, below 0.8 mm pitch, you need to X-ray at least some fraction of the finished boards to check for errors. (Just for the record, the OMAP3517 1 mm packages aren't actually available yet.) If you have other, more specific questions, I'd be glad to try to answer them. - Very concise and informative answer. Thank you. – Imbrondir Dec 28 '10 at 13:56 People don't build their own OMAP boards because you need either 1) an x-ray machine, or 2) extreme patience and experience with re-balling bgas and hot-air rework in order to successfully solder high density bga packages. Also asking why the board costs$200 while the chip costs $15 is like complaining about why software costs money even if you use free and open source compiler and libraries. -  Not complaining. Just want to understand. Thank you. – Imbrondir Dec 28 '10 at 13:53 For a linux system your essential components will be a processor, ram (probably at least ddr) and flash. Then you'll need all the extra stuff, power, lcd connectors, usb, ethernet... any peripherals you want, etc. The Beagle board uses a special POP (package on package) technology where the Flash and RAM are literally mounted onto the top of the OMAP. This is how they can get the board so small. But... it cost some serious dough, like way more than$15.

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As to why the board will cost 200 USD + when the chip is only 15 USD I can give you an answer: You need to check out the other required components: * OMAP: Alright, you'll certainly need that, but how can I power it? * PMIC: Power Management IC, alright, now I have my required 4 voltages, now for some memory * SDRAM: Depending on what you will need, you need an appropriate amount of SDRAM * NAND flash: Definitely you want some non-volatile memory * SD card: Maybe some exchangeable memory * Connectors: Count in the cost for connectors for USB, LAN, eventually you want WLAN Bluetooth or GPS

Alright, now you have the components, but where do you put them on. Designing such a system usually leads to 10 or 12 layer PCBs, eventually including micro-vias, which are not cheap themselves.

Finally, add testing and bring-up of the board, account for a few prototypes before the production can actually start and you have your USD 200 :)

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