can't update bootlader over the air when changing DFU_APP_DATA_RESERVED

Question

I'm trying to update the bootloader over the air, I succeeded to do so following the answer given here 
 it worked when I didn't change big things in the bootloader , but my main purpose is to change DFU_APP_DATA_RESERVED in order to preserve device manager keys which are now erased when DFU performed 
 when I change DFU_APP_DATA_RESERVEDin in the new bootloader I want to flash over the air, the flashing succeed but then nothing boot, not DfuTarg , not my app.

Vidar Berg · Accepted Answer

Changing the DFU_APP_DATA_RESERVED causes the "bank" memory layout to change which the new bootloader cannot foresee. Please have a look at this thread here for more details and a solution. 
 Update 
 dfu_bl_image_validate () is called on startup if softdevice or bootloader update is in progress. This is the normal program flow for BL update: 
 
 Old bootloader loads the new image to swap and sets p_bootloader_settings->bank_1 == BANK_VALID_BOOT followed by a system reset 
 Bootloader starts and
bootloader_dfu_sd_in_progress()
returns 'true' since BANK_VALID_BOOT
is set in bootloader settings. 
 in
bootloader_dfu_sd_update_continue()
the bootloader compares its own image
with the one in swap. If they are
different the old bootloader will
assume that the one in swap is a new
one. In this case it will be
different 
 The comparison will return false so
the bootlaoder runs the
dfu_bl_image_swap() call to replace
itself with the new one (swap is
handled in the MBR). 
 The MBR will start the new bootlaoder
once the copying is complete. 
 BANK_VALID_BOOT will still be set
when the new bootloader starts, but
this time the comparison in
bootloader_dfu_sd_update_continue()
will return success so the bootlaoder
will proceed to
bootloader_dfu_sd_update_finalize()
call and clear the BANK_VALID_BOOT
flag. 
 
 However, in your case the comparison done in the new bootlaoder will fail because of the changed bank1 address.

can't update bootlader over the air when changing DFU_APP_DATA_RESERVED

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