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README: primordial documentation on booting from the external microSD card

feature/booting-external-microsd
Fivel Sotheby 2 years ago
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Booting from the external microSD card
--------------------------------------
TODO

* Insert the external microSD card in the ereader and boot it up.

* Get a shell on the device, either via Telnet, SSH or some sort of terminal emulator.

* On the ereader shell, mount the rootfs as read only and clone the internal memory into the external microSD card:

```
umount /mnt/onboard
mount -o remount,ro /
dd if=/dev/mmcblk0 of=/dev/mmcblk1
```

* Remount the filesystems with their default options:

```
mount -o remount,rw /
mount -t vfat -o noatime,nodiratime,shortname=mixed,utf8 /dev/mmcblk0p3 /mnt/onboard
```

* Remove the microSD card from the ereader and insert it into a computer with a microSD card reader.

* Extract the hardware configuration block from the microSD card. For example, on a GNU/Linux computer, assuming the SD card is at /dev/mmcblk0 (replace as needed):

```
dd bs=512 skip=1024 count=1 if=/dev/mmcblk0 of=ereader.hwconfig
```

* Use a hex editor to change the byte at offset 0x3F (63) from 0 to 1:

```
printf '\x01' | dd of=ereader.hwconfig bs=1 seek=63 count=1 conv=notrunc
```

* Write it back to the microSD card

```
dd if=ereader.hwconfig bs=512 seek=1024 of=/dev/mmcblk0
```

* Proceed with the installation as documented in **Installation on the internal microSD**.

* Hold down the power and backlight buttons while booting until the LED is blinking to boot from the external microSD card.


Notes for developers


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