Serial DFU Commands

See AT Command Format for command syntax.

The serial DFU commands perform a full over-UART firmware upgrade using MCUboot’s image-swap mechanism. The transfer uses RDP (Raw Data Protocol) binary framing rather than ASCII AT commands. The application must route UART bytes to the DFU layer while at_cmd_sysdfu_is_active() returns true.

Typical upgrade sequence:

1. Send AT+SYSDFU=0,<len>,<crc_en> — device replies OK and enters binary-receive mode.

2. Stream the firmware image as a sequence of RDP packets.

3. Send AT+SYSSWITCHBANK= — device marks the staged image for upgrade and reboots.

4. After the reboot, the new firmware runs in unconfirmed state (MCUboot will revert on the next reboot unless confirmed).

5. Send AT+SYSMKBANKGOOD= — device confirms the image; MCUboot will no longer roll back.

RDP Packet Format

Each binary packet carries up to 252 bytes of firmware data:

TX: | HDR (1 B) | SN (1 B) | LEN (1 B) | DATA (0–252 B) |
RX: | HDR (1 B) | SN (1 B) | ERR (1 B) |

HDR op-codes (bits [7:5]):

HDR value	Name	Meaning
0x00	START	First packet of a multi-packet transfer
0x80	CONT	Continuation packet (not the last)
0x20	END	Last packet of a multi-packet transfer
0xA0	CONT+END	Continuation packet that is also the last
0x20	END (single)	Single-packet transfer (only packet, also the last)

The device ACKs each packet. ERR != 0 in the ACK indicates a transfer error; the host must abort and restart from AT+SYSDFU.

AT+SYSDFU — Initiate Serial Firmware Upgrade

Kconfig:

CONFIG_AT_CMD_SYSDFU

Depends:

CONFIG_ATM_VENDOR_DFU

Execute:

AT+SYSDFU=<type>,<length>,<crc_en>

Query:

not supported

Parameter	Description
type	Partition type. Only 0 (firmware) is supported.
length	Total firmware image size in bytes (must be > 0).
crc_en	1 to enable per-packet CRC-8 check, 0 to disable.

Responds OK and immediately enters binary-receive mode. Subsequent UART bytes are interpreted as RDP packets until the full image has been received (END or CONT+END packet). Returns ERR if the DFU subsystem cannot be initialised or if type != 0.

AT+SYSDFU=0,131072,0
OK
<binary RDP stream follows>

AT+SYSSWITCHBANK — Apply Staged Firmware and Reboot

Kconfig:

CONFIG_AT_CMD_SYSDFU

Execute:

AT+SYSSWITCHBANK=

Query:

not supported

Calls atm_vendor_dfu_request_upgrade() to mark the staged image as pending upgrade in MCUboot’s swap state, then schedules a cold reboot. The OK response is transmitted before the reboot occurs.

Returns ERR if the RDP transfer is not complete (AT+SYSDFU was not run or the END/CONT+END packet was not yet received).

AT+SYSSWITCHBANK=
OK
<device reboots and applies the new image>

AT+SYSMKBANKGOOD — Confirm Running Image

Kconfig:

CONFIG_AT_CMD_SYSMKBANKGOOD

Depends:

CONFIG_BOOTLOADER_MCUBOOT

Execute:

AT+SYSMKBANKGOOD=

Query:

not supported

After an MCUboot swap the new image runs in unconfirmed state. If the device reboots again before confirmation, MCUboot will revert to the previous image. This command calls boot_set_confirmed_multi() for every image slot that is pending revert, marking them as permanent.

Send this command after verifying that the new firmware is operating correctly.

AT+SYSMKBANKGOOD=
OK