51 lines
2.3 KiB
Markdown
51 lines
2.3 KiB
Markdown
# SMP over Bluetooth
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This document specifies how the mcumgr Simple Management Procotol (SMP) is
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transmitted over Bluetooth.
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## Overview
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All SMP communication utilizes a single GATT characteristic. An SMP request is
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sent in the form of either 1) a GATT Write Command, or 2) a GATT Write Without
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Response command. An SMP response is sent in the form of a GATT Notification
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specifying the same characteristic that was written.
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If an SMP request or response is too large to fit in a single GATT command, the
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sender fragments it across several commands. No additional framing is
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introduced when a request or response is fragmented; the payload is simply
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split among several commands. Since Bluetooth guarantees ordered delivery of
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packets, the SMP header in the first fragment contains sufficient information
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for reassembly.
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## Services
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### SMP service
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UUID: `8D53DC1D-1DB7-4CD3-868B-8A527460AA84`
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### Characteristics
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#### SMP Characteristic
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| Field | Value |
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| ----- | ----------------------------------------------------------------- |
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| Name | SMP |
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| Description | Used for both SMP requests and responses. |
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| Read | Excluded |
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| Write | Mandatory |
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| WriteWithoutResponse | Mandatory |
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| SignedWrite | Excluded |
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| Notify | Mandatory |
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| Indicate | Excluded |
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| WritableAuxiliaries | Excluded |
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| Broadcast | Excluded |
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| ExtendedProperties | |
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As indicated, SMP requests can be sent in the form of either a Write or a Write
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Without Response. The Write Without Response form is generally preferred, as
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an application-layer response is always sent in the form of a Notification.
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The regular Write form is accepted in case the client requires a GATT response
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to initiate pairing.
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Security for this characteristic is optional.
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