Could I just use .bin to do OTA?

[Alice]

Hi,

When I use nrfutil to generate a zip package, there would be three document in the package. Is there anyone know what does .dat and .json document use for? Could I just use .bin to do OTA?

[shibshab]

Yes you can use a .bin file to perform OTA. Note that you still have to build a DFU zip using nrfutil as described here

.json: Lists the DFU images that should be transferred in the DFU operation.

A single DFU operation can consist of transferring multiple DFU images. For instance, if Softdevice, Bootloader and Application will be updated then this DFU procedure would most likely contain one image for Softdevice+Bootloader and one image for Application. The example below shows the the manifest.json file for such a DFU operation. Note that there are two .dat files (one for each DFU image.)

"manifest": {
    "application": {
        "bin_file": "nrf52832_xxaa_s132.bin",
        "dat_file": "nrf52832_xxaa_s132.dat"
    },
    "softdevice_bootloader": {
        "bin_file": "softdevice_and_bootloader.bin",
        "dat_file": "softdevice_and_bootloader.dat",
        "info_read_only_metadata": {
            "bl_size": 23392,
            "sd_size": 136360
        }
    }
}

.dat: This file is a binary representation of the metadata for each DFU image (called "init packet"). This is described in more detail here. Among other things, it states stuff like what type of upgrade it is and provides the crypto elements needed (signature, SHA etc).