Author Topic: Boot process in pictures  (Read 2204 times)

Destroyer

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Boot process in pictures
« on: March 12, 2011, 08:16:59 AM »
Whilst developing new boot loaders or new operating systems, it is good to have a reference point that you can compare with your own code.

Therefore I present the following information:

Power on:
We have turned the power on and the CPU has started up from cold, we have HALTED U-Boot ready to load the kernel next
at this time there is NO Linux kernel, but U-Boot has been initialized and is ready for commands to be entered.

Console screen


Device LCD


This is the image as seen on the LCD whilst in the U-Boot loader (the extra picture litter, is to ensure I am not accused of using the Emulator to get the image).
At this stage the Kernel is NOT loaded, so from this we can surmise that if when developing our own kernel, we do NOT see this screen(or something similar), that somehow or somewhere there has been an error that has caused U-Boot to fail.

This may be because we have not 'offset' the kernel image with U-Boot at the start, but rather accidentally over written the U-Boot loader either with the file system or with the Kernel image.

A check with a disk editor will answer our question fairly quickly.
« Last Edit: March 12, 2011, 08:24:47 AM by Admin »

tekowalsky

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Re: Boot process in pictures
« Reply #1 on: March 29, 2011, 03:50:54 PM »
Good information.

I think the single best thing we could have right now for these tablets would be a modified u-boot that can optionally boot from the external SD.  The Nook Color uses a modified u-boot to boot from either external SD or from eMMC.

Source for the Nook Color multi- u-boot is located here if anyone else wants to take a crack at porting it:
https://github.com/rookie1/u-boot.git

More advanced version with a boot menu:
https://github.com/j4mm3r/bn_nc_u-boot/tree/boot_menu
« Last Edit: March 29, 2011, 04:07:55 PM by tekowalsky »

Destroyer

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Re: Boot process in pictures
« Reply #2 on: March 31, 2011, 12:09:26 PM »
It really should not be an issue, the U-Boot can boot from any suitable supported device.
There is just a need to get the boot command right, then save it  in the U-Boot options, it is something I am going to look at once my internet connection is re-establised. Currently I'm working sat at a bar, which really is not good for setting up my test equipment.