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Bluetooth: controller: Introduce config for avoiding SDU fragmentation

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The CIS Central uses the algorithm described in BT Core 5.4 Vol 6,
Part G, Section 2.2 to calculate the Max_PDU value for framed mode.

However, HAP needs the Max_PDU to be calculated according to "Core
enhancement for ISOAL CR" coming with the "Atlanta" update. With this
update, the fragmentation is controlled via a parameter at CIG creation.

Enabling CONFIG_BT_CTLR_CONN_ISO_AVOID_SEGMENTATION will set the
ISO_Interval to 7.5 ms for a 10 ms framed CIG, and calculate Max_PDU to
45/65 for 16/24 kHz.

Signed-off-by: Morten Priess <mtpr@oticon.com>
This commit is contained in:
Morten Priess 2023-06-29 09:16:26 +02:00 • committed by Carles Cufí
commit 79ab982f46
2 changed files with 56 additions and 14 deletions
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11
subsys/bluetooth/controller/Kconfig
View file

@ -902,6 +902,17 @@ config BT_CTLR_CONN_ISO_STREAMS_MAX_FT
help
Maximum number of CIS flush timeout events.
config BT_CTLR_CONN_ISO_AVOID_SEGMENTATION
bool "Avoid SDU fragmentation for framed mode"
depends on BT_CTLR_CENTRAL_ISO
help
When creating a CIG, the Max_PDU size is calculated according to BT
Core 5.4 Vol 6, Part G, Section 2.2. However, HAP specifies a need for
avoiding segmentation by forcing the Max_PDU to the appropriate value.
Since there is no way to control the Max_PDU using the non-test
interface, the config provides a way to force the Max_PDU to Max_SDU +
5 (header + offset).
config BT_CTLR_ISO
bool
default BT_CTLR_BROADCAST_ISO || BT_CTLR_CONN_ISO

59
subsys/bluetooth/controller/ll_sw/ull_central_iso.c
View file

@ -234,6 +234,15 @@ uint8_t ll_cig_parameters_commit(uint8_t cig_id, uint16_t *handles)
cig->iso_interval = BT_HCI_ISO_INTERVAL_MIN;
}
#if defined(CONFIG_BT_CTLR_CONN_ISO_AVOID_SEGMENTATION)
/* Check if this is a HAP usecase which requires higher link bandwidth to ensure
* segmentation is not invoked in ISO-AL.
*/
if (cig->central.framing && cig->c_sdu_interval == 10000U) {
cig->iso_interval = 6; /* 7500 us */
}
#endif
if (!cig->central.framing && (cig->c_sdu_interval % ISO_INT_UNIT_US)) {
/* Framing not requested but requirement for unframed is not met. Force
* CIG into framed mode.
@ -1131,29 +1140,51 @@ static void set_bn_max_pdu(bool framed, uint32_t iso_interval,
uint8_t *max_pdu)
{
if (framed) {
uint32_t ceil_f_x_max_sdu;
uint16_t max_pdu_bn1;
uint32_t max_drift;
uint32_t max_drift_us;
uint32_t ceil_f;
/* Framed (From ES-18002):
/* BT Core 5.4 Vol 6, Part G, Section 2.2:
* Max_PDU >= ((ceil(F) x 5 + ceil(F x Max_SDU)) / BN) + 2
* F = (1 + MaxDrift) x ISO_Interval / SDU_Interval
* SegmentationHeader + TimeOffset = 5 bytes
* Continuation header = 2 bytes
* MaxDrift (Max. allowed SDU delivery timing drift) = 100 ppm
*/
max_drift = DIV_ROUND_UP(SDU_MAX_DRIFT_PPM * sdu_interval, 1000000U);
ceil_f = DIV_ROUND_UP(iso_interval + max_drift, sdu_interval);
ceil_f_x_max_sdu = DIV_ROUND_UP(max_sdu * (iso_interval + max_drift),
sdu_interval);
/* Strategy: Keep lowest possible BN.
* TODO: Implement other strategies, possibly as policies.
max_drift_us = DIV_ROUND_UP(SDU_MAX_DRIFT_PPM * sdu_interval, USEC_PER_SEC);
ceil_f = DIV_ROUND_UP((USEC_PER_SEC + max_drift_us) * (uint64_t)iso_interval,
USEC_PER_SEC * (uint64_t)sdu_interval);
if (false) {
#if defined(CONFIG_BT_CTLR_CONN_ISO_AVOID_SEGMENTATION)
/* To avoid segmentation according to HAP, if the ISO_Interval is less than
* the SDU_Interval, we assume BN=1 and calculate the Max_PDU as:
* Max_PDU = celi(F / BN) x (5 / Max_SDU)
*
* This is in accordance with the "Core enhancement for ISOAL CR".
*
* This ensures that the drift can be contained in the difference between
* SDU_Interval and link bandwidth. For BN=1, ceil(F) == ceil(F/BN).
*/
max_pdu_bn1 = ceil_f * 5 + ceil_f_x_max_sdu;
*bn = DIV_ROUND_UP(max_pdu_bn1, LL_CIS_OCTETS_TX_MAX);
*max_pdu = DIV_ROUND_UP(max_pdu_bn1, *bn) + 2;
} else if (iso_interval < sdu_interval) {
*bn = 1;
*max_pdu = ceil_f * (PDU_ISO_SEG_HDR_SIZE + PDU_ISO_SEG_TIMEOFFSET_SIZE +
max_sdu);
#endif
} else {
uint32_t ceil_f_x_max_sdu;
uint16_t max_pdu_bn1;
ceil_f_x_max_sdu = DIV_ROUND_UP(max_sdu * ((USEC_PER_SEC + max_drift_us) *
(uint64_t)iso_interval),
USEC_PER_SEC * (uint64_t)sdu_interval);
/* Strategy: Keep lowest possible BN.
* TODO: Implement other strategies, possibly as policies.
*/
max_pdu_bn1 = ceil_f * (PDU_ISO_SEG_HDR_SIZE +
PDU_ISO_SEG_TIMEOFFSET_SIZE) + ceil_f_x_max_sdu;
*bn = DIV_ROUND_UP(max_pdu_bn1, LL_CIS_OCTETS_TX_MAX);
*max_pdu = DIV_ROUND_UP(max_pdu_bn1, *bn) + PDU_ISO_SEG_HDR_SIZE;
}
} else {
/* For unframed, ISO_Interval must be N x SDU_Interval */
LL_ASSERT(iso_interval % sdu_interval == 0);