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Bluetooth: controller: Implement CIS offset equivalent calculation

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When the 'instant' of a CIS is postponed by increasing the conn_event of
the CIS_RSP compared to CIS_REQ, the CIS offset shall be calculated as
an equivalent window offset by an integer number of ISO intervals.
This is obtained by increasing the CIS_Offset_Min and CIS_Offset_Max by
the modulus of the connection interval delay time.

Signed-off-by: Morten Priess <mtpr@oticon.com>
This commit is contained in:
Morten Priess 2022-09-26 22:35:22 +02:00 • committed by Fabio Baltieri
commit 78c3bf569b
3 changed files with 29 additions and 3 deletions
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28
subsys/bluetooth/controller/ll_sw/ull_llcp_cc.c
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@ -140,14 +140,17 @@ static void rp_cc_check_instant(struct ll_conn *conn, struct proc_ctx *ctx, uint
static void llcp_rp_cc_tx_rsp(struct ll_conn *conn, struct proc_ctx *ctx)
{
struct node_tx *tx;
uint16_t delay_conn_events;
uint16_t conn_event_count;
struct pdu_data *pdu;
struct node_tx *tx;
/* Allocate tx node */
tx = llcp_tx_alloc(conn, ctx);
LL_ASSERT(tx);
pdu = (struct pdu_data *)tx->pdu;
conn_event_count = ctx->data.cis_create.conn_event_count;
/* Postpone if instant is in this or next connection event. This would handle obsolete value
* due to retransmission, as well as incorrect behavior by central.
@ -157,6 +160,29 @@ static void llcp_rp_cc_tx_rsp(struct ll_conn *conn, struct proc_ctx *ctx)
ctx->data.cis_create.conn_event_count = MAX(ctx->data.cis_create.conn_event_count,
ull_conn_event_counter(conn) + 2);
delay_conn_events = ctx->data.cis_create.conn_event_count - conn_event_count;
/* If instant is postponed, calculate the offset to add to CIS_Offset_Min and
* CIS_Offset_Max.
*
* BT Core v5.3, Vol 6, Part B, section 5.1.15:
* Two windows are equivalent if they have the same width and the difference between their
* start times is an integer multiple of ISO_Interval for the CIS.
*
* The offset shall compensate for the relation between ISO- and connection interval. The
* offset translates to what is additionally needed to move the window by an integer number
* of ISO intervals. I.e.:
* offset = (delayed * CONN_interval) MOD ISO_interval
*/
if (delay_conn_events) {
uint32_t conn_interval_us = conn->lll.interval * CONN_INT_UNIT_US;
uint32_t iso_interval_us = ctx->data.cis_create.iso_interval * ISO_INT_UNIT_US;
uint32_t offset_us = (delay_conn_events * conn_interval_us) % iso_interval_us;
ctx->data.cis_create.cis_offset_min += offset_us;
ctx->data.cis_create.cis_offset_max += offset_us;
}
llcp_pdu_encode_cis_rsp(ctx, pdu);
ctx->tx_opcode = pdu->llctrl.opcode;