Redmi Note 12: how to use Slot B for dual-boot?

[zhubr]

Hi all,
I've unlocked the bootloader, installed successfully most current ROM from here as per standard instructions, and installed successfully TWRP also per standard instructions from here. All seems ok. As this is a SD 685 device, it has a full double set of system partitions, _a and _b. I thought it must be very handy for experimenting with alternative ROM versions/OSes without destroying a base usable environment, if I understood this A/B thing correctly.
Now, looking at the the scripts inside of xiaomi.eu_multi_TAPAS_V14.0.14.0.TMTMIXM_v14-13 it seems they install both A and B equally. So I'd suppose if installation was successfull I should be now able to freely switch from A to B with no problem, just to test the method. However, it I go to fastboot and do

fastboot set_active b

then after reboot device gets quite broken. Trying to boot normally, produces a boot loop after Mi Logo. Trying to get into recovery (by holding vol-up) gets stuck at Mi Logo forever. Getting into fastboot (by holding vol-down) works fine though. I've also tried to do multiple set_active b + set_active a + set_active b, as per some recommendations, with no result.

Additionally, I've then looked into some alternative ROM (downloaded elsewhere) and noticed that while flash scripts inside it looked similar, they flash quite more stuff. For instance, they flash standard recovery, which xiaomi.eu_multi_TAPAS_V14.0.14.0.TMTMIXM_v14-13 apparently does not contain. There are some other actions involved there too. Why is that? What else could be missing for successfull Slot B operation?

Note: my device has just been bought and have never obtained any OTA updates.
Any hints and ideas greatly appreciated!

 

[Igor Eisberg]

Slot B is empty, you can't boot from it.

 

[zhubr]

Slot B is empty, you can't boot from it.

Hmm, after those steps like
fastboot flash abl_b abl.img fastboot flash bluetooth_b bluetooth.img ..... fastboot flash boot_b boot.img fastboot flash init_boot_b init_boot.img .....
B is still empty? Ok, then what else is necessary to make it filled?
Or did you mean that somehow slot B is empty for this device no matter what? Then, why the above code for slot B would need to exist?
Sorry for my silly questions and thanks for any hints.

 

[Igor Eisberg]

Hmm, after those steps like
fastboot flash abl_b abl.img fastboot flash bluetooth_b bluetooth.img ..... fastboot flash boot_b boot.img fastboot flash init_boot_b init_boot.img .....
B is still empty? Ok, then what else is necessary to make it filled?
Or did you mean that somehow slot B is empty for this device no matter what? Then, why the above code for slot B would need to exist?
Sorry for my silly questions and thanks for any hints.

I was talking about the super partition. Only Slot A is populated.
As to "what else is necessary", dunno, never tried, and never will...

 

[zhubr]

I was talking about the super partition. Only Slot A is populated.
As to "what else is necessary", dunno, never tried, and never will...

Ah, ok. But in this case I'd suppose going into TWRP recovery from slot B partition should still work regardless of super? Or does TWRP recovery depend on super partition so much that TWRP won't even show up its UI if there is a problem with it?
Thanks!