Author Topic: Build Your Own Linux Powered Pda  (Read 214217 times)

Ferret-Simpson

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« Reply #330 on: July 17, 2006, 08:25:52 am »
Battery:

If it's any bigger than that of a 5600, then who cares? The 5600 battery is 1700mAh anyway, and you could easily fit the SIM socket underneath. (BL08)

Main point about the trackball is that it's basically there for Gaming, and CAD. Anybody who'se that desparate can use an external one, because there's no point in having one if it's in an uncomfortable place because of board shape. If it's going to be a pain in the Derriere to design a board to fit round it then drop it, since it's no good in an awkawrdly placed one.

If we're having connectors around the edge of the case, My point there was that most of them might as well be attached to the Keyboard PCB since it's covering the area of the device anyway.

What's the reason for making the bootloader RO? (You told me there was one, not what it was   ) I thought it was for the sake of Security, which as I said, if the person can use JTAG, they're probably good enough to work another way around the bootloader anyway. (Even if it's a BGA RW Station and a new flash chip.)

And as I listed, those are all reasons to update the bootloader. XP

If people DO lose their key, they'll need to reflash it. If it's flashable by JTAG and nothing else, they can still do that. I mean seriously, how many of the people who would normally steal a device like this can use JTAG? If we keep the documentation of how to do that specifically for the PPZ offline, given only with the hard-copy paperwork of the PPZ anyway, they'll need to ask how to do it. Just make sure they give you the serial number first, and bingo. You've traced the device! Not to mention the concept of the trace program over the modem.

Where do you store the second bootloader, anyway? XP If it's on the ATA or SD, it kinda defeats the object.

I thought the new MD's were out, they might not be. . . They're supposed to be available this year though, we shouldn't have to wait long.

And again, any way to modify that to add USB boot support? I'm guessing it wouldn't be a particular challenge. . Mount the drive and kexec the kernel from it? As I said, would be useful for the Desktop mode, and for people with iPods etc who want to be able to boot from 'em.

As far as the internal ipod drive goes, I was making the point that most people won't need it, or can use it externally, so as far as the PPZ's normal case goes. . better to use a CF socket and keep the case small. PPZ with an extra CM thick for the bigger battery and drive starts to become a little too big for most pockets. Mine, at least. XD
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koen

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« Reply #331 on: July 17, 2006, 08:40:52 am »
Quote
What's the reason for making the bootloader RO?
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It makes the device unbrickable
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Ferret-Simpson

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« Reply #332 on: July 17, 2006, 09:36:00 am »
But if it's only writable from JTAG, chances are that if you know how to flash it once, you know how to flash it again. Right?

I'm not suggesting we make it flashable from OS or anything, just over JTAG. That being the whole point of JTAG in the first plce, right? Flashing and Debugging?
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Da_Blitz

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« Reply #333 on: July 17, 2006, 09:40:39 am »
and a RW bootloader can allow someone to get you encrpytion keys on boot

keyboard PCB might not be made by us, i have seen some people who can do it for us and besides its a bad idea to begin with due to key placment and throgh hole parts

we will be using secure jtag, that requires a code to be sent before flashing

i intend to make this device unhackable if posible, that means not even i can bypass it. it makes it more intresting. if you dont want the extra security then dont enable it or put it on a lower level however i am sure there are a couple of companies who would like somthing this capable. however i ekpect to be yelled at by them when they stuff up and need the data

basically its trusted computing, if you F*** up your F**** (sorry bout the language but i feel its the only way to get the point across) that said you dont have to use the encryption, use the authentication instead

Quote
Where do you store the second bootloader, anyway? XP If it's on the ATA or SD, it kinda defeats the object.

thats why i have the entire encryption and/or authentication so that you can only boot a signed 2nd stage bootloader, what you do from there is your own problem

this thing will boot off anything linux will support

Please remeber this is an Extensible platform, if someone wants a bigger case they can buy a bigger case

i really have to simplify this now. i think i should not comment on the case but focus on the PCB and follow the princibles of simplicity and extensability
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Da_Blitz

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« Reply #334 on: July 17, 2006, 09:43:23 am »
once its debuged i am removing the jtag port.
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Ferret-Simpson

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« Reply #335 on: July 17, 2006, 01:58:39 pm »
Ok. next question: Can the Linux Encrypted Bootloader kexec the kernels of other OS's? For example. .  FreeBSD, OpenBSD, AROS. . .?

Ok, for me. . . Just AROS. But is it capable of that? That's a biiiig one for me.
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km2783

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« Reply #336 on: July 17, 2006, 02:04:34 pm »
FYI, the ipod recharges when connected to a USB port.  Make sure to modify the cable so it can't.
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koen

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« Reply #337 on: July 17, 2006, 02:08:58 pm »
Quote
FYI, the ipod recharges when connected to a USB port.  Make sure to modify the cable so it can't.
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The ipod negotiates the current draw first, so you can instruct linux not to charge it.
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Da_Blitz

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« Reply #338 on: July 17, 2006, 09:05:36 pm »
kexec can execute any binary image regardless of what it is. as long as it runs on the hardware it can exec it (this is how tho openBSD peopel boot on the Z)
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Da_Blitz

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« Reply #339 on: July 17, 2006, 09:08:04 pm »
i also discorvered the problem with the dns, the client i was using fails silently. no error message or exit code to indicate a lack of update (very bad programming practice)

updating by hand at the moment but my IP is alot more stable now
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Tom61

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« Reply #340 on: July 18, 2006, 12:28:20 am »
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once its debuged i am removing the jtag port.
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Err, then how are we supposed to get the bootloader on then? Wouldn't the secure JTAG be signed agianst the number in the iMX, which we wouldn't know initially?

Quote
And as I listed, those are all reasons to update the bootloader. XP

Let me guess, you're still using LILO.  I've put multiple kernels, including going from 2.4 series to 2.6 series kernels without redoing GRUB. One just needs to update the config and put the kernel/initrd in /boot, which is in a rw partition. With a more embedded system, you just name the kernel/initrd the right name, and in this system, have to sign it with the correct key to load it.

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« Reply #341 on: July 18, 2006, 02:39:49 am »
its a real chiken and egg problem till you look at the data sheet and relise that you can send this thing code to be executed over usb

when faced between the option of flashing over usb or jtag i think more people would have a usb port than jtag equipment

onec everything is flashed then we can disable flashing over the usb port (must double check that)
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Nemuri Neko

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« Reply #342 on: July 18, 2006, 02:57:23 am »
Ok, lets get rid of the flash slowing down the SDRAM meme. The flash whether NAND or NOR will not slow down the SDRAM in any meaningful way. They only share a bus in the sense that they both use AMBA peripherals to the CPU, but the arbiter will mean things move along at a good pace. If you want to look at the real culprit for system slowdown then begin to look at the LCD. Having a look at some of the app notes the iMX looks to have to hand over up to 70% of available bandwidth for a VGA screen running 3d graphics, this will only get worse as the resolution increases. This includes using the 3d engine so has a high pixel rate that would only be seen in games.
Now, these tests were done using 16 bit SDRAM, and I think the plan is to use 32bit mobile DDR SDRAM so this whould halve the memory requirements. But this is something to keep in mind if you want the result to run 3d apps.

Over to the keyboard, thinking about having a membrane over keyswitches.... I'm not sure how that will work. I have seen membrane keyboards, but these usually have a conductive layer over a spiral of etch, so when the "key" is pressed then the contact is made. The best adaption of this I have seen are in old HP calculators and pocket computers. These had a separate keycap pivoted above a shallow metal dome. this gave very good key feel for not much vertical height.

Surface mount keyswitches will definitely provide the best feel for a keyboard, but even the most shallow of these are tall, add to that the keycap that has to be placed over it and you have a keyboard with a height of 5mm or over. a better solution is to pivot the keycap below the upper deck height of the keyswitch, but this is very hard to engineer.

Last time I did something similar Fujitsu had some nice embedded keyboards off the shelf, but they are larger than I think this forum wants. Check out the following pdf

http://www.fceu.fujitsu.com/pdf/Datasheet_FKB-7681.pdf

The amount of things in this design may very well mean that a keyboard of this size is useable. They definitely feel ok to type on.

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« Reply #343 on: July 18, 2006, 03:02:01 am »
Quote
its a real chiken and egg problem till you look at the data sheet and relise that you can send this thing code to be executed over usb

when faced between the option of flashing over usb or jtag i think more people would have a usb port than jtag equipment

onec everything is flashed then we can disable flashing over the usb port (must double check that)
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First boot can be done over USB, and thus a loader can be loaded  Then a change in jumpers, or fuse burn can disable this option. There will be nothing that can be done about a determined engineer re-flashing, but data already flashed should be able to be made safe. It is not tamper proof, but is what the datasheet describes as tamper evident.

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« Reply #344 on: July 18, 2006, 03:07:08 am »
Do we have an IRC channel to have a chat? cos some of this is going to get very loooong and very technical. Toys will be thrown, chickens counted and milk spilled before things are finalised, all of which is going to take up a lot of pages on this board