This version (26 Oct 2023 11:14) was approved by Sanjeeva Reddy.

Appendix B: Messages

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Messages are shared between the Stack, Plugins and the Application to request or notify specific events.

Request Message

Request Message Example:-

Figure: Request Message Example

The list of Request message commands is listed below.

Request Message Commands
CommandsDescriptionPayload Type
A2B_MSGREQ_UNKNOWNUnknown message request command, typically to indicate error -
A2B_MSGREQ_NET_RESET Reset the A2B network-
A2B_MSGREQ_NET_DISCOVERY Start A2B network discoverya2b_NetDiscovery
A2B_MSGREQ_NET_DISCOVERY_DIAGMODEStart A2B network discovery in diag modeNot supported
A2B_MSGREQ_PLUGIN_PERIPH_INIT Request directed to a slave plugin to complete any necessary initialization of peripherals attached to the slave nodea2b_PluginInit
A2B_MSGREQ_PLUGIN_PERIPH_DEINIT Request directed to a slave plugin to de-initialize any peripherals attached to the slave nodea2b_PluginDeinit
A2B_MSGREQ_PLUGIN_VERSION Request directed to a master or slave plugin for version and build information about this plugin itselfa2b_PluginVerInfo
A2B_MSGREQ_CUSTOM Arbitrary custom command-
A2B_MSGREQ_NET_POST_DISCOVERYStarts partial discovery attempt of dropped nodesa2b_NetPostDiscovery

Table: Request Message Commands

Notify Messages

Notify Message Examples:-

Figure: Notify Message Example

The list of Notify Message Commands is listed below

Notify Message CommandsDescriptionPayload type
A2B_MSGNOTIFY_GPIO_INTERRUPTNotify type used when a plugin triggers a GPIO interrupt.Causes an interrupt notification to be emitted
A2B_MSGNOTIFY_POWER_FAULT Notify type used when a plugin sends a power fault notificationa2b_PowerFault
A2B_MSGNOTIFY_INTERRUPT Notify type used when the stack detects any interrupt and emits a notification.This also includes any GPIO-related interruptsa2b_Interrupt
A2B_MSGNOTIFY_DISCOVERY_DONENotification that is emitted at the end of discovery whether it resulted in success or failure. This message also captures whether audio host provided SYNC to master PLL for locking (MSTR_RUNNING).a2b_DiscoveryStatus
A2B_MSGNOTIFY_CUSTOM Arbitrary custom command.Anything at or beyond this value is considered a custom command -
A2B_MSGNOTIFY_NODE_DISCOVERYNotify type used when the stack discovers a node OR custom node authentication fails for a particular node.a2b_Nodedscvry

Table: Notify Message Commands

Sending custom messages and notifications

To send a custom message, one must allocate the message, find the payload area, deposit the message contents, send the message, and optionally release the reference to the message. Sending a typical message looks like this:

Code Snippet: Sending Custom Message Example

Code Snippet: ending Custom Message Example

As illustrated in the example code above, the caller unreferences the message following the call to a2b_msgRtrSendRequest(). This is because the Stack adds its own reference to the message following the send request. In the event that caller requires that the message live longer, i.e. because it is carrying pointers to data, then one should register a complete callback with the a2b_msgRtrSendRequest() and unreference the message there.

The callee of the message is free to modify the contents of the message within the callee’s message handler. A callback optionally registered by the caller can be called when the callee completes processing of the message. This callback can be used by the caller to process return values from the callee.

Receiving custom messages and notifications

Messages are handled exclusively through the Execute method of a plugin. A plugin simply has to have defined entries for custom message within the switch/case statement. The message payload can be extracted from the message using ‘a2b_msgGetPayload()’

Code snippet: Receiving Custom Message Example

Code Snippet: Receiving Custom Message Example

resources/tools-software/a2bv2/a2bssplusstackuserguide/messages.txt · Last modified: 10 Oct 2023 09:44 by Sanjeeva Reddy