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Bluetooth: Controller: Add margin to ISOALs time offset

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To ensure payloads are delivered in time for the first subevent
in framed BIS, ISOAL now enforces a (configurable) margin of
the calculated time offset

Without this margin, it has been observed that a broadcaster
can end up consistently missing the first subevent in every third
event in a 7.5 ms ISO with a 10 ms SDU interval

The margin is a conservative 2 ms by default, but can likely be
set a lot lower for most implementations and HWs

Signed-off-by: Troels Nilsson <trnn@demant.com>
This commit is contained in:
Troels Nilsson 2024-09-10 16:06:09 +02:00 • committed by Anas Nashif
commit fa3bfa5453
4 changed files with 47 additions and 4 deletions
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19
subsys/bluetooth/controller/Kconfig.ll_sw_split
View file

@ -616,6 +616,25 @@ config BT_CTLR_ISOAL_PSN_IGNORE
help
Ignore the use of Tx ISO Data Packet Sequence Number.
config BT_CTLR_ISOAL_FRAMED_BIS_OFFSET_MARGIN
int "Margin (in microseconds) to be used in framed time offset for BIS"
depends on BT_CTLR_ADV_ISO || BT_CTLR_CONN_ISO
default 2000
range 0 10000
help
Needed margin for reliable delivery of payloads will vary, but should
generally be EVENT_OVERHEAD_START_US + a small margin to cover ISOAL
processing overhead
config BT_CTLR_ISOAL_FRAMED_CIS_OFFSET_MARGIN
int "Margin (in microseconds) to be used in framed time offset for CIS"
depends on BT_CTLR_ADV_ISO || BT_CTLR_CONN_ISO
default 0
range 0 10000
help
Note: Usually no margin is needed for CIS as null PDUs can be used if a payload
is too late for the first subevent
config BT_CTLR_ZLI
bool "Use Zero Latency IRQs"
depends on ZERO_LATENCY_IRQS

10
subsys/bluetooth/controller/ll_sw/isoal.c
View file

@ -1519,7 +1519,7 @@ static isoal_status_t isoal_check_source_hdl_valid(isoal_source_handle_t hdl)
* @param pdu_release[in] Callback of PDU deallocator
* @param hdl[out] Handle to new source
*
* @return ISOAL_STATUS_OK if we could create a new sink; otherwise ISOAL_STATUS_ERR_SOURCE_ALLOC
* @return ISOAL_STATUS_OK if we could create a new source; otherwise ISOAL_STATUS_ERR_SOURCE_ALLOC
*/
isoal_status_t isoal_source_create(
uint16_t handle,
@ -1550,6 +1550,7 @@ isoal_status_t isoal_source_create(
session->handle = handle;
session->framed = framed;
session->bis = role == ISOAL_ROLE_BROADCAST_SOURCE;
session->burst_number = burst_number;
session->iso_interval = iso_interval;
session->sdu_interval = sdu_interval;
@ -2343,6 +2344,9 @@ static uint16_t isoal_tx_framed_find_correct_tx_event(const struct isoal_source
const bool time_stamp_is_valid = isoal_is_time_stamp_valid(source_ctx,
tx_sdu->cntr_time_stamp,
tx_sdu->time_stamp);
const uint16_t offset_margin = session->bis ?
CONFIG_BT_CTLR_ISOAL_FRAMED_BIS_OFFSET_MARGIN :
CONFIG_BT_CTLR_ISOAL_FRAMED_CIS_OFFSET_MARGIN;
/* Adjust payload number */
if (pp->initialized) {
@ -2437,7 +2441,7 @@ static uint16_t isoal_tx_framed_find_correct_tx_event(const struct isoal_source
* The Time_Offset shall be a positive value.
*/
while (!isoal_get_time_diff(time_stamp_selected, actual_grp_ref_point, &time_diff)
|| time_diff == 0) {
|| time_diff <= offset_margin) {
/* Advance target to next event */
actual_event++;
actual_grp_ref_point = isoal_get_wrapped_time_us(actual_grp_ref_point,
@ -2525,7 +2529,7 @@ static isoal_status_t isoal_tx_framed_produce(isoal_source_handle_t source_hdl,
uint64_t next_payload_number;
uint16_t sdus_skipped;
bool time_diff_valid;
uint32_t time_diff;
uint32_t time_diff = 0U;
/* Start of a new SDU */
time_diff_valid = isoal_get_time_diff(session->last_input_time_stamp,

3
subsys/bluetooth/controller/ll_sw/isoal.h
View file

@ -376,7 +376,8 @@ struct isoal_source_session {
uint32_t sdu_interval;
uint16_t handle;
uint16_t iso_interval;
uint8_t framed;
uint8_t framed: 1;
uint8_t bis: 1;
uint8_t burst_number;
uint8_t pdus_per_sdu;
uint8_t max_pdu_size;

19
tests/bluetooth/controller/ctrl_isoal/Kconfig
View file

@ -57,6 +57,25 @@ config BT_CTLR_ISOAL_SN_STRICT
depends on BT_CTLR_ADV_ISO || BT_CTLR_CONN_ISO
default y
config BT_CTLR_ISOAL_FRAMED_BIS_OFFSET_MARGIN
int "Margin (in microseconds) to be used in framed time offset for BIS"
depends on BT_CTLR_ADV_ISO || BT_CTLR_CONN_ISO
default 2000
range 0 10000
help
Needed margin for reliable delivery of payloads will vary, but should
generally be EVENT_OVERHEAD_START_US + a small margin to cover ISOAL
processing overhead
config BT_CTLR_ISOAL_FRAMED_CIS_OFFSET_MARGIN
int "Margin (in microseconds) to be used in framed time offset for CIS"
depends on BT_CTLR_ADV_ISO || BT_CTLR_CONN_ISO
default 0
range 0 10000
help
Note: Usually no margin is needed for CIS as Null PDUs can be used if a payload
is too late for the first subevent
source "tests/bluetooth/controller/common/Kconfig"
source "Kconfig.zephyr"