Here now comes the SD-Card and Rom level changes :
YOU MUST USE ATLEAST CLASS 6 OR ABOVE SDCARD WITH MINIMUM 8GB CAPACITY
First you need 3 EXT4 partitions on SD-card, using minitool partition wizard
1) around 400 MB - SD-SYSTEM (ext4)
2) around 1 GB (or can be less) - SD-DATA(ext4 format),
3)around 75MB (can be less) SD-CACHE(ext4 format) (refer to the screenshot):
Rom level changes :
Get the updater-script of your Primary rom and find for these lines (Will differ from device to device
- but basically the format is same )
format("yaffs2", "MTD", "system", "0", "/system");
mount("yaffs2", "MTD", "system", "/system");
Now replace it with :
run_program("/sbin/busybox", "mount", "-t", "auto", "/dev/block/mmcblk0p2", "/system");
run_program("/sbin/busybox", "rm", "-rf", "/system/*");
-what we are doing here is extracting the sustem files to the sd-ext partition we just created earlier
save it and replace this updater-script in the original Primary rom and also replace the boot.img with the one you made earlier.
That's it.If you have followed the guide correctly you can Dual boot any Rom on your device
Now flash the primary rom first.. and then any rom you choose as the secondary rom (PROVIDED IT DOESN"T USE SD-Ext partitions..) and flash it
REMEMBER DO NOT wipe data before installing the secondary rom
If you want to change your secondary rom DO NOT WIPE DATA instead goto recovery -
if in CWM or philz
-go to mounts and storage and format
[B][COLOR="red"]system , data and cache
For Switching roms :
-put the boot.img of primary rom in the root of your sd-card(not in any directory) reanme it primary.img
-put the boot.img of secondary rom in the root of your sd-card(not in any directory) reanme it sec.img
-get terminal emulator app
flash_image boot /sdcard/primary.img (or secondary.img)
But STOP here are some restrictions of this method :
You must make sure your device uses boot.img format and you know your device's correct mount points !! if you do it wrong you WILL hard brick your device !!
1. For The secondary rom you CANNOT use scripts like int2ext, etc.
2. Also you CANNOT use pll2 OC method in Secondary ROM
3. The edited cm10beta 6 (primary rom) is clocked at 600mhz, so NO chances of burnt nand.
4. You can choose ANY rom as secondary ROM provided it does not violate the first 2 clauses, that is, it should not use sd-ext partitions
5. The process is only for people having class 6 or higher sd card.
PS : This has taken a lot of effort and time so please don't go on commenting "This is useless" , "i don't like it" ,etc. If you don't like it, you are free to leave.