: Place the extracted firmware files (often named rootfs-3521a ) directly in the root directory of the USB drive, not inside any folders.

: Many DVR brands using the HI3521A chipset provide firmware updates. For example, Zosi Support offers upgrade files for models using the Hi3521A chip.

: Sites like Unifore compile firmware lists for HiSilicon SoC-based DVRs, including the Hi3521A series.

: If prompted for a password during the upgrade process, many systems use a default like 123456 . General Flashing Procedure Format USB : Use a flash drive formatted to FAT32 .

Finding a specific "flash dump" for a HiSilicon-based DVR like the HI3521A V123 1080N16

: Insert the drive into the DVR's USB port and navigate to System > Maintenance > Upgrade (the exact path varies by brand). V4.02.R11 H.264/H.265 DVR/NVR Firmware Download

While direct ".rar" download links for specific flash dumps are often hosted on technician forums, you can find official and compatible firmware from these sources:

Before downloading, you must verify your exact hardware version to avoid "bricking" the device: