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att_server: document delayed write

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Matthias Ringwald 2024-07-19 16:25:38 +02:00
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2 changed files with 15 additions and 0 deletions
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8
doc/manual/docs-template/profiles.md
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@ -633,6 +633,8 @@ Similar to other protocols, it might be not possible to send any time.
To send a Notification, you can call *att_server_request_to_send_notification*
to request a callback, when yuo can send the Notification.
### Deferred Handling of ATT Read / Write Requests
If your application cannot handle an ATT Read Request in the *att_read_callback*
in some situations, you can enable support for this by adding ENABLE_ATT_DELAYED_RESPONSE
to *btstack_config.h*. Now, you can store the requested attribute handle and return
@ -646,6 +648,12 @@ When you've got the data for all requested attributes ready, you can call
Please keep in mind that there is only one active ATT operation and that it has a 30 second
timeout after which the ATT server is considered defunct by the GATT Client.
Similarly, you can return ATT_ERROR_WRITE_RESPONSE_PENDING in the *att_write_callback*.
The ATT Server will not respond to the ATT Client in this case and wait for your code to
call *att_server_response_ready*, which then triggers the *att_write_callback* again.
Please have a look at the [ATT Delayed Response example](../examples/examples/#sec:attdelayedresponseExample).
### Implementing Standard GATT Services {#sec:GATTStandardServices}
Implementation of a standard GATT Service consists of the following 4 steps:

7
src/ble/att_db.h
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@ -127,13 +127,17 @@ typedef struct att_connection {
#define ATT_READ_RESPONSE_PENDING 0xffffu
// internally used to signal write response pending
// To ask ATT Server to defer the write response, you can return ATT_ERROR_WRITE_RESPONSE_PENDING in your att_write_callback
#define ATT_INTERNAL_WRITE_RESPONSE_PENDING 0xfffeu
/**
* @brief ATT Client Read Callback for Dynamic Data
* - if buffer == NULL, don't copy data, just return size of value
* - if buffer != NULL, copy data and return number bytes copied
*
* If ENABLE_ATT_DELAYED_READ_RESPONSE is defined, you may return ATT_READ_RESPONSE_PENDING if data isn't available yet
* and call att_server_response_ready to re-trigger the callback.
*
* @param con_handle of hci le connection
* @param attribute_handle to be read
* @param offset defines start of attribute value
@ -152,6 +156,9 @@ typedef uint16_t (*att_read_callback_t)(hci_con_handle_t con_handle, uint16_t at
*
* If the additional validation step is not needed, just return 0 for all callbacks with transaction mode ATT_TRANSACTION_MODE_VALIDATE.
*
* If ENABLE_ATT_DELAYED_READ_RESPONSE is defined, you may return ATT_ERROR_WRITE_RESPONSE_PENDING if data isn't available yet
* and call att_server_response_ready to re-trigger the callback.
*
* @param con_handle of hci le connection
* @param attribute_handle to be written
* @param transaction - ATT_TRANSACTION_MODE_NONE for regular writes. For prepared writes: ATT_TRANSACTION_MODE_ACTIVE, ATT_TRANSACTION_MODE_VALIDATE, ATT_TRANSACTION_MODE_EXECUTE, ATT_TRANSACTION_MODE_CANCEL