central device will not raise security level with new periphral if no power reset on central side

[LongQi]

The central device has the below settings

static void auth_passkey_entry(struct bt_conn *conn)
{
	char addr[BT_ADDR_LE_STR_LEN];

	bt_addr_le_to_str(bt_conn_get_dst(conn), addr, sizeof(addr));

	// Check for passkey entry event
	unsigned int passkey = STATIC_PASSKEY;
	LOG_DBG("Passkey entered %s: %06u", addr, passkey);

	// Set passkey using bt_conn_auth_passkey_entry()
	bt_conn_auth_passkey_entry(conn, passkey);
}

static void auth_cancel(struct bt_conn *conn)
{
	char addr[BT_ADDR_LE_STR_LEN];

	bt_addr_le_to_str(bt_conn_get_dst(conn), addr, sizeof(addr));

	LOG_INF("Pairing cancelled: %s", addr);
}

static void pairing_complete(struct bt_conn *conn, bool bonded)
{
	char addr[BT_ADDR_LE_STR_LEN];

	bt_addr_le_to_str(bt_conn_get_dst(conn), addr, sizeof(addr));

	LOG_INF("Pairing completed: %s, bonded: %d", addr, bonded);
}

static void pairing_failed(struct bt_conn *conn, enum bt_security_err reason)
{
	char addr[BT_ADDR_LE_STR_LEN];

	bt_addr_le_to_str(bt_conn_get_dst(conn), addr, sizeof(addr));

	LOG_ERR("Pairing failed conn: %s, reason %d", addr, reason);
}

static struct bt_conn_auth_cb conn_auth_callbacks = {
	.passkey_entry = auth_passkey_entry,
	.cancel        = auth_cancel,
};

static struct bt_conn_auth_info_cb conn_auth_info_callbacks = {
	.pairing_complete = pairing_complete,
	.pairing_failed   = pairing_failed
};

One central device A and two peripheral devices B and C,  B and C have the exact same firmware. A can establish the connection with B or C. 

but I have to power reset A in order to change the connection between A-B and A-C otherwise auth_passkey_entry on A will not be triggered and security level will always be the lowest.

I tried to do power reset B and C but the situation still remain the same. 

Is there any flag or bonding info I need to clear on the central side before establish a new connection ?

[Simonr]

The key handling for pairing is handled in the BLE Host, and uses settings that are by default to store the keys persistently in flash. It is highly recommended not to use RAM for this due to its volatile nature, so we do not have an alternative like this available. I'm sorry, but it will be up to you to tweak the host layer if this is necessary.

Best regards,

Simon

[LongQi]

1. How to calculate the flash size needed for the keys persistent and how to partition for this purpose?

2. How to "tweak the host layer"? Is there any guide document and sample application?