Few question about the CM

[Narf03]

I didnt know the existence of this sub-forum, and i posted these questions on
http://www.raspberrypi.org/raspberry-pi ... w-product/

Since its not being answer yet, maybe I should ask them here =)

1) How good is the eMMC against corruption ? We know that there is a chance of corruption will happen if we simply cut power for Model A and B, but both A and B uses SD card, and CM uses eMMC, will it still be the same(which we cannot simply cut power) ?

2) Is it possible to make the eMMC read-only and only writing data to other media(to prevent system corruption) ? like USB Flash drive / HDD ?

3) How much total bandwidth can we expect from the USB ports ? 480mb/s ? Shared with eMMC ?

4) Can all DSI(s) & HDMI & composite working at the same time ? Or what is the limits ?

5) I am a software engineer, so please tell me is it easy/difficult for a hardware engineer to design our own IO board with RJ45 ? Where is the MAC address from ?

6) Regarding the price, $30 is just the CM itself or with the IO board ?

Thanks alot

[RaTTuS]

1) dunno , but if you building a board then put some abttery on it and sense the power fail and then close down cleanly
2) probably no need
3) usb is the same as on the Model A -
4) yes
5) you will need to add a Network chip like on the model B
6) that is the compute module - the IO board is extra but you use that instead of making your own

[clacktronics]

5) I am a software engineer, so please tell me is it easy/difficult for a hardware engineer to design our own IO board with RJ45 ? Where is the MAC address from ?

Usually set in the interface IC itself i think
http://en.wikipedia.org/wiki/MAC_address

see a random IC datasheet
http://www.micrel.com/_PDF/Ethernet/dat ... snl_ds.pdf

I would say tricky if you have no PCB and Electronics experience but not impossible! keep in mind a lot of parts needed for development with the CM are going to be tiny!

[rpdom]

The MAC address for the standard ethernet connection on a model B pi is generated from the six hex digits of the Raspberry Pi foundation MAC range (b8:27:eb) and the last six hex digits of the Pi serial number.

This only applies to the LAN9512 interface, any USB wifi or lan interfaces will have their own MAC addresses.

I suspect the CM will work the same way, as it has the same firmware and OS.

[jdb]

I didnt know the existence of this sub-forum, and i posted these questions on
http://www.raspberrypi.org/raspberry-pi ... w-product/

Since its not being answer yet, maybe I should ask them here =)

1) How good is the eMMC against corruption ? We know that there is a chance of corruption will happen if we simply cut power for Model A and B, but both A and B uses SD card, and CM uses eMMC, will it still be the same(which we cannot simply cut power) ?

eMMC devices have additional safeguards against breaking them by yanking the power in the middle of a write. The FTL inside them is capable of running in a copy-on-write mode: it's painfully slow but guarantees that all block writes either fail and report failure or succeed across power cycles.

2) Is it possible to make the eMMC read-only and only writing data to other media(to prevent system corruption) ? like USB Flash drive / HDD ?

Yes. Sections of the eMMC device can be made "one-time programmable" by sending it a set of specialised commands that render a block range read-only. The FTL understands this and will not write to the flash pages at all.

3) How much total bandwidth can we expect from the USB ports ? 480mb/s ? Shared with eMMC ?

The eMMC uses the SD interface. It's an SD card with all the useless bits removed. The maximum USB bandwidth is a function of transport type and how well you can program realtime applications: I believe gsh has managed to get 2x720p streams out of BCM2835 over an isochronous transport.

4) Can all DSI(s) & HDMI & composite working at the same time ? Or what is the limits ?

The display output combinations are a function of how many different ways you can configure the pixel valves - there are 3 on BCM2835, which means a theoretical limit of 3 displays. HDMI cannot be functional at the same time as composite as they share a pixel valve.

[Narf03]

eMMC devices have additional safeguards against breaking them by yanking the power in the middle of a write. The FTL inside them is capable of running in a copy-on-write mode: it's painfully slow but guarantees that all block writes either fail and report failure or succeed across power cycles.

Does that mean eMMC will be much slower compare to a normal SD card(reading and writing or writing only) ?

Yes. Sections of the eMMC device can be made "one-time programmable" by sending it a set of specialised commands that render a block range read-only. The FTL understands this and will not write to the flash pages at all.

Does that mean, I can no longer flash the eMMC anymore ? Lets say i done it wrongly, can it be reset ?

Thank you very much.

[jamesh]

One time programmable is exactly that. But you don't have to make anything OTP if you don't what to. As I understand it...

[Bertold]

Hello,

You can also temporary write protect the SD Card so you can revert it if you need to change the contents later. I have made a program to do this: http://bertold.org/sdtool/ (it very likely also works for eMMC)

Note that this program uses the CSD write protection flags so it locks the entire card. If there is interest I can add the commands to only lock certain pages.

[Briarios]

I have a question as well. will the Compute Module already have an OS already installed? or will we need to flash our own?

[fruitoftheloom]

I have a question as well. will the Compute Module already have an OS already installed? or will we need to flash our own?

No OS pre-installed...

[jamesh]

But it's easy to install - takes a couple of minutes once you know what you are doing.

http://www.raspberrypi.org/documentatio ... /README.md

[Briarios]

Thanks for that guys, now I know on what is needed

[alexeames]

But it's easy to install - takes a couple of minutes once you know what you are doing.

http://www.raspberrypi.org/documentatio ... /README.md

Took me 20 minutes to flash June 2014 Raspbian using an old Ubuntu laptop
(that was the flashing time, not the setting up or anything).