: Navigate to Main Menu > Information > System (or Version ) to find your current firmware build and hardware ID.
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: Download FLASH DUMP DVR HI3521A V123 1080N16 rar
: Place the extracted firmware files (often named rootfs-3521a ) directly in the root directory of the USB drive, not inside any folders. : Navigate to Main Menu > Information >
: If the DVR won't boot, open the casing and look for the printed hardware model and version directly on the board. including the Hi3521A series.
: Sites like Unifore compile firmware lists for HiSilicon SoC-based DVRs, including the Hi3521A series.