Bluetooth: controller: Introduce config for avoiding SDU fragmentation (79ab982f) · Commits · Wenxi XU / zephyr

subsys/bluetooth/controller/Kconfig

+11 −0

Original line number	Diff line number	Diff line
		@@ -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

subsys/bluetooth/controller/ll_sw/ull_central_iso.c

+45 −14

Original line number	Diff line number	Diff line
		@@ -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);
		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).
		*/
		} 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 * 5 + ceil_f_x_max_sdu;
		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) + 2;
		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);

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