| # SMP over console |
| |
| This document specifies how the mcumgr Simple Management Procotol (SMP) is |
| transmitted over text consoles. |
| |
| ## Overview |
| |
| Mcumgr packets sent over serial are fragmented into frames of 127 bytes or |
| fewer. This 127-byte maximum applies to the entire frame, including header, |
| CRC, and terminating newline. |
| |
| The initial frame in a packet has the following format: |
| |
| ``` |
| offset 0: 0x06 0x09 |
| === Begin base64 encoding === |
| offset 2: <16-bit packet-length> |
| offset ?: <body> |
| offset ?: <crc16> (if final frame) |
| === End base64 encoding === |
| offset ?: 0x0a (newline) |
| ``` |
| |
| All subsequent frames have the following format: |
| |
| ``` |
| offset 0: 0x04 0x14 |
| === Begin base64 encoding === |
| offset 2: <body> |
| offset ?: <crc16> (if final frame) |
| === End base64 encoding === |
| offset ?: 0x0a (newline) |
| ``` |
| |
| All integers are represented in big-endian. The packet fields are described |
| below: |
| |
| | Field | Description | |
| | ----- | ----------- | |
| | 0x06 0x09 | Byte pair indicating the start of a packet. | |
| | 0x04 0x14 | Byte pair indicating the start of a continuation frame. | |
| | Packet length | The combined total length of the *unencoded* body plus the final CRC (2 bytes). Length is in Big-Endian format. | |
| | Body | The actual SMP data (i.e., 8-byte header and CBOR key-value map). | |
| | CRC16 | A CRC16 of the *unencoded* body of the entire packet. This field is only present in the final frame of a packet. | |
| | Newline | A 0x0a byte; terminates a frame. | |
| |
| The packet is fully received when <packet-length> bytes of body has been |
| received. |
| |
| ## CRC details |
| |
| The CRC16 should be calculated with the following parameters: |
| |
| | Field | Value | |
| | ------------- | ------------- | |
| | Polynomial | 0x1021 | |
| | Initial Value | 0 | |
