Will sys_reboot(SYS_REBOOT_COLD) clear the flag bit set by bootmode_set(BOOT_MODE_TYPE_BOOTLOADER)? (Attempted in the DFU upgrade routine by pressing a key (l9_e1_sol).)

RE: Will sys_reboot(SYS_REBOOT_COLD) clear the flag bit set by bootmode_set(BOOT_MODE_TYPE_BOOTLOADER)? (Attempted in the DFU upgrade routine by pressing a key (l9_e1_sol).)

Menon — Fri, 13 Mar 2026 07:29:29 GMT

Hello,

Glad to hear that the issue has been resolved.

Kind regards,

Abhijith

RE: Will sys_reboot(SYS_REBOOT_COLD) clear the flag bit set by bootmode_set(BOOT_MODE_TYPE_BOOTLOADER)? (Attempted in the DFU upgrade routine by pressing a key (l9_e1_sol).)

bobo Chen — Fri, 13 Mar 2026 06:42:51 GMT

Now this problem has been solved.

Root Cause Summary

The issue was that the boot mode retention backend was incorrectly configured in the Devicetree overlay files.

What went wrong

The original overlay used gpregret1 (a hardware General Purpose Retention Register) as the backend for the boot mode retention system. While gpregret1 is a valid hardware peripheral, it did not work reliably for the bootmode_set() → MCUboot Serial Recovery flow on the nRF54L15.

What fixed it

Replacing gpregret1 with a dedicated non-initialized RAM region (sram@2003FFFF) as the retention backend resolved the issue. This is the approach documented in the Zephyr retention subsystem. [Boot mode docs]

Key requirements for `bootmode_set()` to work

Both the application and MCUboot must define the same retention node (same RAM address and size) in their respective Devicetree overlays, and assign it to the zephyr,boot-mode chosen node.
MCUboot must have CONFIG_BOOT_SERIAL_BOOT_MODE=y enabled in mcuboot.conf to read the boot mode value on startup.
The application must have CONFIG_RETENTION_BOOT_MODE=y (and related options) enabled in prj.conf to write the boot mode value.
The application must call bootmode_set(BOOT_MODE_TYPE_BOOTLOADER) followed by sys_reboot(0) to trigger the transition into Serial Recovery mode.

RE: Will sys_reboot(SYS_REBOOT_COLD) clear the flag bit set by bootmode_set(BOOT_MODE_TYPE_BOOTLOADER)? (Attempted in the DFU upgrade routine by pressing a key (l9_e1_sol).)

bobo Chen — Fri, 13 Mar 2026 01:42:38 GMT

devzone.nordicsemi.com/.../2543.build.rar

Hello,

It runs on the demo board, and the attachment is the build folder.

thanks

RE: Will sys_reboot(SYS_REBOOT_COLD) clear the flag bit set by bootmode_set(BOOT_MODE_TYPE_BOOTLOADER)? (Attempted in the DFU upgrade routine by pressing a key (l9_e1_sol).)

Menon — Thu, 12 Mar 2026 14:08:46 GMT

Hello,

sys_reboot(SYS_REBOOT_COLD) should not clear the boot mode flag set by bootmode_set(BOOT_MODE_TYPE_BOOTLOADER). bootmode_set() is to store the boot mode in a retained memory region so that the value survives after a reset. After reboot, MCUboot checks this value. If it detects BOOT_MODE_TYPE_BOOTLOADER, it clears the flag and enters serial recovery mode. See the section bootmode.

Are you working with a custom board here? If possible, could you share the generated build folder?

Kind Regards,

Abhijith

Will sys_reboot(SYS_REBOOT_COLD) clear the flag bit set by bootmode_set(BOOT_MODE_TYPE_BOOTLOADER)? (Attempted in the DFU upgrade routine by pressing a key (l9_e1_sol).)

RE: Will sys_reboot(SYS_REBOOT_COLD) clear the flag bit set by bootmode_set(BOOT_MODE_TYPE_BOOTLOADER)? (Attempted in the DFU upgrade routine by pressing a key (l9_e1_sol).)

RE: Will sys_reboot(SYS_REBOOT_COLD) clear the flag bit set by bootmode_set(BOOT_MODE_TYPE_BOOTLOADER)? (Attempted in the DFU upgrade routine by pressing a key (l9_e1_sol).)

Now this problem has been solved.Root Cause Summary

What went wrong

What fixed it

Key requirements for bootmode_set() to work

RE: Will sys_reboot(SYS_REBOOT_COLD) clear the flag bit set by bootmode_set(BOOT_MODE_TYPE_BOOTLOADER)? (Attempted in the DFU upgrade routine by pressing a key (l9_e1_sol).)

RE: Will sys_reboot(SYS_REBOOT_COLD) clear the flag bit set by bootmode_set(BOOT_MODE_TYPE_BOOTLOADER)? (Attempted in the DFU upgrade routine by pressing a key (l9_e1_sol).)

Now this problem has been solved.

Root Cause Summary

Key requirements for `bootmode_set()` to work