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Bluetooth: controller: Make random force on lost anchor configurable

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Legacy functionality in ull_conn will force scheduling of a connection
which has missed an anchor point due to lost RX. This kicks in either
for previously skipped events (latenzy_event != 0) or at random
depending on the randomness of the AA bit pattern.

This behavior is good at ensuring that a connection with errors or
aborted RX gets prioitized, and helps break locked round-robin
patterns with lost sync, but it also breaks the predictability of
the round-robin ticker scheduling.

With "must_expire" enabled, this feature also kicks in for scheduling
collisions, which may not be desirable.

This commit adds a configuration flag, BT_CTLR_CONN_RANDOM_FORCE, which
is default enabled (legacy behavior).

Signed-off-by: Morten Priess <mtpr@oticon.com>
This commit is contained in:
Morten Priess 2020-11-22 23:02:15 +01:00 • committed by Carles Cufí
commit 18c01ecae8
2 changed files with 16 additions and 2 deletions
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14
subsys/bluetooth/controller/Kconfig.ll_sw_split
View file

@ -431,6 +431,20 @@ config BT_CTLR_FORCE_MD_AUTO
Force MD bit in transmitted PDU based on runtime incoming transmit
data throughput.
config BT_CTLR_CONN_RANDOM_FORCE
bool "Enable random forced scheduling for peripheral on missed anchor point"
depends on BT_PERIPHERAL
default y
help
When enabled, controller will have legacy behavior and randomly force
priority at next ticker scheduling for peripheral role, if anchor point is
missed.
Two or more connections with similar interval on a device connected
to a peer device having two or more connections at its end with same
interval could lock to a round robin pattern where in neither of the central
nor peripheral event would be in sync at either end. Randomness allows
to break this locked round robin pattern permitting an anchor point sync.
config BT_CTLR_CONN_RSSI_EVENT
bool "Connection RSSI event"
depends on BT_CTLR_CONN_RSSI

4
subsys/bluetooth/controller/ll_sw/ull_conn.c
View file

@ -1164,7 +1164,7 @@ void ull_conn_done(struct node_rx_event_done *done)
if (conn->supervision_expire <= 6U) {
force = 1U;
}
#if defined(CONFIG_BT_PERIPHERAL)
#if defined(CONFIG_BT_CTLR_CONN_RANDOM_FORCE)
/* use randomness to force slave role when anchor
* points are being missed.
*/
@ -1181,7 +1181,7 @@ void ull_conn_done(struct node_rx_event_done *done)
}
}
}
#endif /* CONFIG_BT_PERIPHERAL */
#endif /* CONFIG_BT_CTLR_CONN_RANDOM_FORCE */
} else {
conn_cleanup(conn, BT_HCI_ERR_CONN_TIMEOUT);