3. Changes to Amazon Sidewalk stack configuration

struct sid_gsk_config, declared in sid_gsk_config.h, carries the GSK tunables: pass a pointer to it in sid_config.gsk_config and call sid_init(). All three fields apply to sub-GHz links only. gsk_config is not conditionally excluded and is read even when both SID_SDK_CONFIG_ENABLE_LINK_TYPE_2 and SID_SDK_CONFIG_ENABLE_LINK_TYPE_3 are 0, but no link then exists that could carry a session. In a build with SID_SDK_CONFIG_ENABLE_GSK (sid_sdk_config.h, default 1) set to 0, none of the three fields is read at all, no session is ever established, and nothing in this note applies; see the Gateway Session Key configuration section of the Amazon Sidewalk Sid API Developer Guide.

Field	Range and default	Meaning
`idle_timeout_sec` (`uint32_t`, seconds)	10–600 s (`SID_GSK_IDLE_TIMEOUT_MIN_SEC`, `SID_GSK_IDLE_TIMEOUT_MAX_SEC`); `0` = 240 s default (`SID_GSK_IDLE_TIMEOUT_DEFAULT_SEC`).	The quiet window required on sub-GHz message traffic, both directions, before an establishment starts (§2.2). It is a floor on how long the lull must last, not a deadline: the actual wait can be longer. The keep-alive interval caps any usable value (§4, §6).
`app_ack_miss_threshold` (`uint32_t`, count)	3–10 (`SID_GSK_APP_ACK_MISS_MIN`, `SID_GSK_APP_ACK_MISS_MAX`); `0` = 6 default (`SID_GSK_APP_ACK_MISS_DEFAULT`).	Consecutive ack-requested uplinks transmitted but never acknowledged end to end, after which the session is discarded and the link continues in non-GSK mode. §2.2 gives what feeds the counter, what resets it, and what the counted uplinks cost.
`retry_interval_sec` (`uint32_t`, seconds)	43200–129600 s, that is 12–36 h (`SID_GSK_RETRY_INTERVAL_MIN_SEC`, `SID_GSK_RETRY_INTERVAL_MAX_SEC`); `0` = 86400 s default, one day (`SID_GSK_RETRY_INTERVAL_DEFAULT_SEC`).	How long the Endpoint stays in non-GSK mode after a fallback before it retries establishment. The wait repeats until one succeeds, and each attempt still waits for the idle window (§2.2).

Table 3.1: Fields of struct sid_gsk_config.

Rules:

A NULL gsk_config pointer selects all three defaults — 240 s, 6 and 86400 s; a field value of 0 selects that field’s default independently.
Out-of-range values are silently clamped to the nearest bound, so sid_init() never fails because of gsk_config, and no API reads back the applied value. Assert your values against the SID_GSK_* macros at compile time (§5).
No sid_option retunes any of the three fields: call sid_deinit(), then sid_init() again.
sid_gsk_config.h includes only <stdint.h> and sid_api.h does not include it, so include it yourself. With the SDK’s CMake targets, link the header-only sid_gsk_config target for its include path; sid_api does not expose it.

What a retune costs. sid_deinit() does not discard the stored session, so the following sid_init() reloads it exactly as a reboot does (§2.2): if it is no longer usable, the Endpoint spends up to one retry_interval_sec in non-GSK mode. Retune only in good coverage, and prefer a compile-time constant.

sid_stop() and sid_start() do not move the session lifecycle.