Bluetooth: Mesh: access tx msg randomizer

Commit adds implementation of the specification
recommendations regarding randomization of
responses on the access layer.
3.7.3.1 Transmitting an Access messages

Signed-off-by: Aleksandr Khromykh <aleksandr.khromykh@nordicsemi.no>

doc/connectivity/bluetooth/api/mesh/access.rst

@@ -222,6 +222,39 @@ They are used to represent the new content of the mirrored pages when the Compos
 change after a firmware update. See :ref:`bluetooth_mesh_dfu_srv_comp_data_and_models_metadata`
 for details.
 
+Delayable messages
+==================
+
+The delayable message functionality is enabled with Kconfig option
+:kconfig:option:`CONFIG_BT_MESH_ACCESS_DELAYABLE_MSG`.
+This is an optional functionality that implements specification recommendations for
+messages that are transmitted by a model in a response to a received message, also called
+response messages.
+
+Response messages should be sent with the following random delays:
+
+* Between 20 and 50 milliseconds if the received message was sent
+  to a unicast address
+* Between 20 and 500 milliseconds if the received message was sent
+  to a group or virtual address
+
+The delayable message functionality is triggered if the :c:member:`bt_mesh_msg_ctx.rnd_delay`
+flag is set.
+The delayable message functionality stores messages in the local memory while they are
+waiting for the random delay expiration.
+
+If the transport layer doesn't have sufficient memory to send a message at the moment
+the random delay expires, the message is postponed for another 10 milliseconds.
+If the transport layer cannot send a message for any other reason, the delayable message
+functionality raises the :c:member:`bt_mesh_send_cb.start` callback with a transport layer
+error code.
+
+If the delayable message functionality cannot find enough free memory to store an incoming
+message, it will send messages with delay close to expiration to free memory.
+
+When the mesh stack is suspended or reset, messages not yet sent are removed and
+the :c:member:`bt_mesh_send_cb.start` callback is raised with an error code.
+
 API reference
 *************
 

doc/releases/release-notes-3.6.rst

@@ -52,6 +52,11 @@ Bluetooth
 
 * Mesh
 
+  * Added the delayable messages functionality to apply random delays for
+    the transmitted responses on the Access layer.
+    The functionality is enabled by the :kconfig:option:`CONFIG_BT_MESH_ACCESS_DELAYABLE_MSG`
+    Kconfig option.
+
 * Controller
 
 Boards & SoC Support

include/zephyr/bluetooth/mesh/msg.h

@@ -98,6 +98,9 @@ struct bt_mesh_msg_ctx {
 	/** Force sending reliably by using segment acknowledgment */
 	bool  send_rel;
 
+	/** Send message with a random delay according to the Access layer transmitting rules. */
+	bool  rnd_delay;
+
 	/** TTL, or BT_MESH_TTL_DEFAULT for default TTL. */
 	uint8_t  send_ttl;
 };

samples/bluetooth/mesh/boards/bbc_microbit.conf

@@ -32,3 +32,4 @@ CONFIG_BT_MESH_SUBNET_COUNT=1
 CONFIG_BT_MESH_APP_KEY_COUNT=1
 CONFIG_BT_MESH_MODEL_GROUP_COUNT=1
 CONFIG_BT_MESH_LABEL_COUNT=0
+CONFIG_BT_MESH_ACCESS_DELAYABLE_MSG=n

samples/bluetooth/mesh_demo/boards/bbc_microbit.conf

@@ -22,3 +22,4 @@ CONFIG_BT_MESH_BEACON_ENABLED=n
 CONFIG_BT_MESH_LABEL_COUNT=1
 
 CONFIG_BT_MESH_SETTINGS_WORKQ=n
+CONFIG_BT_MESH_ACCESS_DELAYABLE_MSG=n

subsys/bluetooth/mesh/CMakeLists.txt

@@ -122,6 +122,8 @@ zephyr_library_sources_ifdef(CONFIG_BT_MESH_SOLICITATION solicitation.c)
 
 zephyr_library_sources_ifdef(CONFIG_BT_MESH_STATISTIC statistic.c)
 
+zephyr_library_sources_ifdef(CONFIG_BT_MESH_ACCESS_DELAYABLE_MSG delayable_msg.c)
+
 if (CONFIG_BT_MESH_USES_TINYCRYPT)
     zephyr_library_sources(crypto_tc.c)
 else()

subsys/bluetooth/mesh/Kconfig

@@ -628,6 +628,41 @@ config BT_MESH_LABEL_NO_RECOVER
 	  unprovisioned before upgrading to the version with this option). The option is marked as
 	  deprecated to remove the recovery code eventually.
 
+menuconfig BT_MESH_ACCESS_DELAYABLE_MSG
+	bool "Access layer tx delayable message"
+	help
+	  Enable following of the message transmitting recommendations, the Access layer
+	  specification. The recommendations are optional.
+	  However, they are strictly recommended if the device participates in the network with
+	  intensive communication where the device receives a lot of requests that require responses.
+
+if BT_MESH_ACCESS_DELAYABLE_MSG
+
+config BT_MESH_ACCESS_DELAYABLE_MSG_COUNT
+	int "Number of simultaneously delayed messages"
+	default 4
+	help
+	  The maximum number of messages the Access layer can manage to delay
+	  at the same time. The number of messages can be handled only if the Access layer
+	  has a sufficient amount of memory to store the model payload for them.
+
+config BT_MESH_ACCESS_DELAYABLE_MSG_CHUNK_SIZE
+	int "Maximum delayable message storage chunk"
+	default 20
+	help
+	  Size of memory that Access layer uses to split model message to. It allocates
+	  a sufficient number of these chunks from the pool to store the full model payload.
+
+config BT_MESH_ACCESS_DELAYABLE_MSG_CHUNK_COUNT
+	int "Maximum number of available chunks"
+	default 20
+	help
+	  The maximum number of available chunks the Access layer allocates to store model payload.
+	  It is recommended to keep chunk size equal to the reasonable small value to prevent
+	  unnecessary memory wasting.
+
+endif # BT_MESH_ACCESS_DELAYABLE_MSG
+
 endmenu # Access layer
 
 menu "Models"

subsys/bluetooth/mesh/access.c

@@ -27,6 +27,7 @@
 #include "op_agg.h"
 #include "settings.h"
 #include "va.h"
+#include "delayable_msg.h"
 
 #define LOG_LEVEL CONFIG_BT_MESH_ACCESS_LOG_LEVEL
 #include <zephyr/logging/log.h>
@@ -1518,6 +1519,13 @@ int bt_mesh_model_send(const struct bt_mesh_model *model, struct bt_mesh_msg_ctx
 		return -EINVAL;
 	}
 
+#if defined CONFIG_BT_MESH_ACCESS_DELAYABLE_MSG
+	if (ctx->rnd_delay) {
+		return bt_mesh_delayable_msg_manage(ctx, msg, bt_mesh_model_elem(model)->rt->addr,
+						    cb, cb_data);
+	}
+#endif
+
 	return bt_mesh_access_send(ctx, msg, bt_mesh_model_elem(model)->rt->addr, cb, cb_data);
 }
 
@@ -2613,3 +2621,24 @@ uint8_t bt_mesh_comp_parse_page(struct net_buf_simple *buf)
 
 	return page;
 }
+
+void bt_mesh_access_init(void)
+{
+#if defined CONFIG_BT_MESH_ACCESS_DELAYABLE_MSG
+	bt_mesh_delayable_msg_init();
+#endif
+}
+
+void bt_mesh_access_suspend(void)
+{
+#if defined CONFIG_BT_MESH_ACCESS_DELAYABLE_MSG
+	bt_mesh_delayable_msg_stop();
+#endif
+}
+
+void bt_mesh_access_reset(void)
+{
+#if defined CONFIG_BT_MESH_ACCESS_DELAYABLE_MSG
+	bt_mesh_delayable_msg_stop();
+#endif
+}

subsys/bluetooth/mesh/access.h

@@ -96,8 +96,25 @@ void bt_mesh_msg_cb_set(void (*cb)(uint32_t opcode, struct bt_mesh_msg_ctx *ctx,
  *
  * @param ctx The Bluetooth Mesh message context.
  * @param buf The message payload.
+ * @param src_addr The source address of model
+ * @param cb Callback function.
+ * @param cb_data Callback data.
  *
  * @return 0 on success or negative error code on failure.
  */
 int bt_mesh_access_send(struct bt_mesh_msg_ctx *ctx, struct net_buf_simple *buf, uint16_t src_addr,
 			const struct bt_mesh_send_cb *cb, void *cb_data);
+
+/** @brief Initialize the Access layer.
+ *
+ * Initialize the delayable message mechanism if it has been enabled.
+ */
+void bt_mesh_access_init(void);
+
+/** @brief Suspend the Access layer.
+ */
+void bt_mesh_access_suspend(void);
+
+/** @brief Reset the Access layer.
+ */
+void bt_mesh_access_reset(void);

subsys/bluetooth/mesh/delayable_msg.c

@@ -0,0 +1,314 @@
+/*
+ * Copyright (c) 2023 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <zephyr/kernel.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <zephyr/sys/slist.h>
+
+#include <zephyr/net/buf.h>
+#include <zephyr/bluetooth/mesh.h>
+
+#include "msg.h"
+#include "access.h"
+#include "net.h"
+
+#define LOG_LEVEL CONFIG_BT_MESH_ACCESS_LOG_LEVEL
+#include <zephyr/logging/log.h>
+LOG_MODULE_REGISTER(bt_mesh_delayable_msg);
+
+static void delayable_msg_handler(struct k_work *w);
+static bool push_msg_from_delayable_msgs(void);
+
+static struct delayable_msg_chunk {
+	sys_snode_t node;
+	uint8_t data[CONFIG_BT_MESH_ACCESS_DELAYABLE_MSG_CHUNK_SIZE];
+} delayable_msg_chunks[CONFIG_BT_MESH_ACCESS_DELAYABLE_MSG_CHUNK_COUNT];
+
+static struct delayable_msg_ctx {
+	sys_snode_t node;
+	sys_slist_t chunks;
+	struct bt_mesh_msg_ctx ctx;
+	uint16_t src_addr;
+	const struct bt_mesh_send_cb *cb;
+	void *cb_data;
+	uint32_t fired_time;
+	uint16_t len;
+} delayable_msgs_ctx[CONFIG_BT_MESH_ACCESS_DELAYABLE_MSG_COUNT];
+
+static struct {
+	sys_slist_t busy_ctx;
+	sys_slist_t free_ctx;
+	sys_slist_t free_chunks;
+	struct k_work_delayable random_delay;
+} access_delayable_msg = {.random_delay = Z_WORK_DELAYABLE_INITIALIZER(delayable_msg_handler)};
+
+static void put_ctx_to_busy_list(struct delayable_msg_ctx *ctx)
+{
+	struct delayable_msg_ctx *curr_ctx;
+	sys_slist_t *list = &access_delayable_msg.busy_ctx;
+	sys_snode_t *head = sys_slist_peek_head(list);
+	sys_snode_t *curr = head;
+	sys_snode_t *prev = curr;
+
+	if (!head) {
+		sys_slist_append(list, &ctx->node);
+		return;
+	}
+
+	do {
+		curr_ctx = CONTAINER_OF(curr, struct delayable_msg_ctx, node);
+		if (ctx->fired_time < curr_ctx->fired_time) {
+			if (curr == head) {
+				sys_slist_prepend(list, &ctx->node);
+			} else {
+				sys_slist_insert(list, prev, &ctx->node);
+			}
+			return;
+		}
+		prev = curr;
+	} while ((curr = sys_slist_peek_next(curr)));
+
+	sys_slist_append(list, &ctx->node);
+}
+
+static struct delayable_msg_ctx *peek_pending_msg(void)
+{
+	struct delayable_msg_ctx *pending_msg = NULL;
+	sys_snode_t *node = sys_slist_peek_head(&access_delayable_msg.busy_ctx);
+
+	if (node) {
+		pending_msg = CONTAINER_OF(node, struct delayable_msg_ctx, node);
+	}
+
+	return pending_msg;
+}
+
+static void reschedule_delayable_msg(struct delayable_msg_ctx *msg)
+{
+	uint32_t curr_time;
+	k_timeout_t delay = K_NO_WAIT;
+	struct delayable_msg_ctx *pending_msg;
+
+	if (msg) {
+		put_ctx_to_busy_list(msg);
+	}
+
+	pending_msg = peek_pending_msg();
+
+	if (!pending_msg) {
+		return;
+	}
+
+	curr_time = k_uptime_get_32();
+	if (curr_time < pending_msg->fired_time) {
+		delay = K_MSEC(pending_msg->fired_time - curr_time);
+	}
+
+	k_work_reschedule(&access_delayable_msg.random_delay, delay);
+}
+
+static int allocate_delayable_msg_chunks(struct delayable_msg_ctx *msg, int number)
+{
+	sys_snode_t *node;
+
+	for (int i = 0; i < number; i++) {
+		node = sys_slist_get(&access_delayable_msg.free_chunks);
+		if (!node) {
+			LOG_WRN("Unable allocate %u chunks, allocated %u", number, i);
+			return i;
+		}
+		sys_slist_append(&msg->chunks, node);
+	}
+
+	return number;
+}
+
+static void release_delayable_msg_chunks(struct delayable_msg_ctx *msg)
+{
+	sys_snode_t *node;
+
+	while ((node = sys_slist_get(&msg->chunks))) {
+		sys_slist_append(&access_delayable_msg.free_chunks, node);
+	}
+}
+
+static struct delayable_msg_ctx *allocate_delayable_msg_ctx(void)
+{
+	struct delayable_msg_ctx *msg;
+	sys_snode_t *node;
+
+	if (sys_slist_is_empty(&access_delayable_msg.free_ctx)) {
+		LOG_WRN("Purge pending delayable message.");
+		if (!push_msg_from_delayable_msgs()) {
+			return NULL;
+		}
+	}
+
+	node = sys_slist_get(&access_delayable_msg.free_ctx);
+	msg = CONTAINER_OF(node, struct delayable_msg_ctx, node);
+	sys_slist_init(&msg->chunks);
+
+	return msg;
+}
+
+static void release_delayable_msg_ctx(struct delayable_msg_ctx *ctx)
+{
+	if (sys_slist_find_and_remove(&access_delayable_msg.busy_ctx, &ctx->node)) {
+		sys_slist_append(&access_delayable_msg.free_ctx, &ctx->node);
+	}
+}
+
+static bool push_msg_from_delayable_msgs(void)
+{
+	sys_snode_t *node;
+	struct delayable_msg_chunk *chunk;
+	struct delayable_msg_ctx *msg = peek_pending_msg();
+	uint16_t len = msg->len;
+	int err;
+
+	if (!msg) {
+		return false;
+	}
+
+	NET_BUF_SIMPLE_DEFINE(buf, BT_MESH_TX_SDU_MAX);
+
+	SYS_SLIST_FOR_EACH_NODE(&msg->chunks, node) {
+		uint16_t tmp = MIN(CONFIG_BT_MESH_ACCESS_DELAYABLE_MSG_CHUNK_SIZE, len);
+
+		chunk = CONTAINER_OF(node, struct delayable_msg_chunk, node);
+		memcpy(net_buf_simple_add(&buf, tmp), chunk->data, tmp);
+		len -= tmp;
+	}
+
+	msg->ctx.rnd_delay = false;
+	err = bt_mesh_access_send(&msg->ctx, &buf, msg->src_addr, msg->cb, msg->cb_data);
+	msg->ctx.rnd_delay = true;
+
+	if (err == -EBUSY || err == -ENOBUFS) {
+		return false;
+	}
+
+	release_delayable_msg_chunks(msg);
+	release_delayable_msg_ctx(msg);
+
+	if (err && msg->cb && msg->cb->start) {
+		msg->cb->start(0, err, msg->cb_data);
+	}
+
+	return true;
+}
+
+static void delayable_msg_handler(struct k_work *w)
+{
+	if (!push_msg_from_delayable_msgs()) {
+		sys_snode_t *node = sys_slist_get(&access_delayable_msg.busy_ctx);
+		struct delayable_msg_ctx *pending_msg =
+			CONTAINER_OF(node, struct delayable_msg_ctx, node);
+
+		pending_msg->fired_time += 10;
+		reschedule_delayable_msg(pending_msg);
+	} else {
+		reschedule_delayable_msg(NULL);
+	}
+}
+
+int bt_mesh_delayable_msg_manage(struct bt_mesh_msg_ctx *ctx, struct net_buf_simple *buf,
+				 uint16_t src_addr, const struct bt_mesh_send_cb *cb, void *cb_data)
+{
+	sys_snode_t *node;
+	struct delayable_msg_ctx *msg;
+	uint16_t random_delay;
+	int total_number = DIV_ROUND_UP(buf->size, CONFIG_BT_MESH_ACCESS_DELAYABLE_MSG_CHUNK_SIZE);
+	int allocated_number = 0;
+	uint16_t len = buf->len;
+
+	if (atomic_test_bit(bt_mesh.flags, BT_MESH_SUSPENDED)) {
+		LOG_WRN("Refusing to allocate message context while suspended");
+		return -ENODEV;
+	}
+
+	if (total_number > CONFIG_BT_MESH_ACCESS_DELAYABLE_MSG_CHUNK_COUNT) {
+		return -EINVAL;
+	}
+
+	msg = allocate_delayable_msg_ctx();
+	if (!msg) {
+		LOG_WRN("No available free delayable message context.");
+		return -ENOMEM;
+	}
+
+	do {
+		allocated_number +=
+			allocate_delayable_msg_chunks(msg, total_number - allocated_number);
+
+		if (total_number > allocated_number) {
+			LOG_DBG("Unable allocate %u chunks, allocated %u", total_number,
+				allocated_number);
+			if (!push_msg_from_delayable_msgs()) {
+				LOG_WRN("No available chunk memory.");
+				release_delayable_msg_chunks(msg);
+				release_delayable_msg_ctx(msg);
+				return -ENOMEM;
+			}
+		}
+	} while (total_number > allocated_number);
+
+	SYS_SLIST_FOR_EACH_NODE(&msg->chunks, node) {
+		uint16_t tmp = MIN(CONFIG_BT_MESH_ACCESS_DELAYABLE_MSG_CHUNK_SIZE, buf->len);
+
+		struct delayable_msg_chunk *chunk =
+			CONTAINER_OF(node, struct delayable_msg_chunk, node);
+
+		memcpy(chunk->data, net_buf_simple_pull_mem(buf, tmp), tmp);
+	}
+
+	bt_rand(&random_delay, sizeof(uint16_t));
+	random_delay = 20 + random_delay % (BT_MESH_ADDR_IS_UNICAST(ctx->recv_dst) ? 30 : 480);
+	msg->fired_time = k_uptime_get_32() + random_delay;
+	msg->ctx = *ctx;
+	msg->src_addr = src_addr;
+	msg->cb = cb;
+	msg->cb_data = cb_data;
+	msg->len = len;
+
+	reschedule_delayable_msg(msg);
+
+	return 0;
+}
+
+void bt_mesh_delayable_msg_init(void)
+{
+	sys_slist_init(&access_delayable_msg.busy_ctx);
+	sys_slist_init(&access_delayable_msg.free_ctx);
+	sys_slist_init(&access_delayable_msg.free_chunks);
+
+	for (int i = 0; i < CONFIG_BT_MESH_ACCESS_DELAYABLE_MSG_COUNT; i++) {
+		sys_slist_append(&access_delayable_msg.free_ctx, &delayable_msgs_ctx[i].node);
+	}
+
+	for (int i = 0; i < CONFIG_BT_MESH_ACCESS_DELAYABLE_MSG_CHUNK_COUNT; i++) {
+		sys_slist_append(&access_delayable_msg.free_chunks, &delayable_msg_chunks[i].node);
+	}
+}
+
+void bt_mesh_delayable_msg_stop(void)
+{
+	sys_snode_t *node;
+	struct delayable_msg_ctx *ctx;
+
+	k_work_cancel_delayable(&access_delayable_msg.random_delay);
+
+	while ((node = sys_slist_peek_head(&access_delayable_msg.busy_ctx))) {
+		ctx = CONTAINER_OF(node, struct delayable_msg_ctx, node);
+		release_delayable_msg_chunks(ctx);
+		release_delayable_msg_ctx(ctx);
+
+		if (ctx->cb && ctx->cb->start) {
+			ctx->cb->start(0, -ENODEV, ctx->cb_data);
+		}
+	}
+}

subsys/bluetooth/mesh/delayable_msg.h

@@ -0,0 +1,16 @@
+/*
+ * Copyright (c) 2023 Nordic Semiconductor ASA
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#ifndef ZEPHYR_INCLUDE_BLUETOOTH_MESH_DELAYABLE_MSG_H__
+#define ZEPHYR_INCLUDE_BLUETOOTH_MESH_DELAYABLE_MSG_H__
+
+int bt_mesh_delayable_msg_manage(struct bt_mesh_msg_ctx *ctx, struct net_buf_simple *buf,
+				 uint16_t src_addr, const struct bt_mesh_send_cb *cb,
+				 void *cb_data);
+void bt_mesh_delayable_msg_init(void);
+void bt_mesh_delayable_msg_stop(void);
+
+#endif /* ZEPHYR_INCLUDE_BLUETOOTH_MESH_DELAYABLE_MSG_H__ */

subsys/bluetooth/mesh/main.c

@@ -359,6 +359,7 @@ void bt_mesh_reset(void)
 	 */
 	(void)k_work_cancel_delayable(&bt_mesh.ivu_timer);
 
+	bt_mesh_access_reset();
 	bt_mesh_model_reset();
 	bt_mesh_cfg_default_set();
 	bt_mesh_trans_reset();
@@ -459,6 +460,8 @@ int bt_mesh_suspend(void)
 
 	bt_mesh_model_foreach(model_suspend, NULL);
 
+	bt_mesh_access_suspend();
+
 	err = bt_mesh_adv_disable();
 	if (err) {
 		atomic_clear_bit(bt_mesh.flags, BT_MESH_SUSPENDED);
@@ -558,6 +561,7 @@ int bt_mesh_init(const struct bt_mesh_prov *prov,
 	bt_mesh_cfg_default_set();
 	bt_mesh_net_init();
 	bt_mesh_trans_init();
+	bt_mesh_access_init();
 	bt_mesh_hb_init();
 	bt_mesh_beacon_init();
 	bt_mesh_adv_init();