Hi,
we are implementing MCUmgr SMP OTA over BLE (Zephyr + nRF54L15) with flutter, and I want to confirm that I’m generating the correct SMP upload packet format before streaming firmware to the device.
What we have done so far,
1- Chunked the firmware into 120-byte blocks.
- We tried chunkSize = 400, but this caused:
GenericFailure<WriteCharacteristicFailure>(code: WriteCharacteristicFailure.unknown, message: "GATT exception from MAC='XX:XX:XX:XX:XX:XX', status 19 (GATT_CONN_TERMINATE_PEER_USER), type BleGattOperation{description='CHARACTERISTIC_WRITE'}.
we reduced to chunkSize = 120, ( 120 bytes binary -> ~160 bytes Base64 -> ~180–200 bytes final SMP packet )
2- Built correct SMP Upload Packets (Header + CBOR + Base64)
- for packet zero,
{
"off": 0,
"data": "<base64>",
"len": <full firmware size>
}
others,
{
"off": <offset>,
"data": "<base64>"
} - And header we use this format,
[
0x02, // Operation: Write request
0x00, // Flags
(cborBytes.length >> 8) & 0xFF, // Payload length (high byte)
cborBytes.length & 0xFF, // Payload length (low byte)
0x00, 0x04, // Group = 0x0004 (Image Management)
seq & 0xFF, // Seq number
0x01, // Command = 0x01 (Upload)
].
But the notification response from device shows: { "rc" = 8 }.
seq & 0xFF, // Seq number
Should seq be always less than 256 ?
Can anyone help identify the fix for this problem or share the correct packet format (header + CBOR) that Zephyr/nRF MCUmgr expects?
