fix(nimble): Added api to query available ACL packets

nimble/host/include/host/ble_hs_hci.h

@@ -102,6 +102,17 @@ int ble_hs_hci_set_chan_class(const uint8_t *chan_map);
  */
 int ble_hs_hci_util_rand(void *dst, int len);
 
+/**
+ * Returns the number of available ACL transmit buffers on the controller.
+ *
+ * Applications can use this to implement notification throttling — only
+ * enqueue new notifications when available buffers are above a waterline.
+ *
+ * @return  The number of ACL packet buffers the controller can currently
+ *          accept from the host.
+ */
+uint16_t ble_hs_hci_get_avail_pkts(void);
+
 #if MYNEWT_VAL(BLE_HCI_VS)
 /**
  * Send an arbitrary HCI command to the controller.

nimble/host/src/ble_hs_hci.c

@@ -271,7 +271,7 @@ typedef struct {
     uint16_t             hci_max_pkts;
     uint64_t             hci_sup_feat;
     uint8_t              hci_version;
-    uint16_t             hci_avial_pkts;
+    uint16_t             hci_avail_pkts;
 
     struct os_mempool    hci_frag_mempool;      /* Memory pool for HCI fragments */
     os_membuf_t         *hci_frag_data;         /* Memory buffer backing HCI pool */
@@ -289,7 +289,8 @@ static ble_hs_hci_ctx_t *ble_hs_hci_ctx = NULL;
 #define ble_hs_hci_max_pkts           (ble_hs_hci_ctx->hci_max_pkts)
 #define ble_hs_hci_sup_feat           (ble_hs_hci_ctx->hci_sup_feat)
 #define ble_hs_hci_version            (ble_hs_hci_ctx->hci_version)
-#define ble_hs_hci_avail_pkts         (ble_hs_hci_ctx->hci_avial_pkts)
+#undef ble_hs_hci_avail_pkts
+#define ble_hs_hci_avail_pkts         (ble_hs_hci_ctx->hci_avail_pkts)
 
 #define ble_hs_hci_frag_mempool     (ble_hs_hci_ctx->hci_frag_mempool)
 #define ble_hs_hci_frag_data        (ble_hs_hci_ctx->hci_frag_data)
@@ -315,6 +316,9 @@ uint16_t ble_hs_hci_avail_pkts;
 static struct ble_hci_ev *l_ble_hs_hci_ack;
 #endif //BLE_STATIC_TO_DYNAMIC
 
+/* Indicates HCI mutex / state has been initialized and can be safely read. */
+static uint8_t ble_hs_hci_initialized;
+
 #if CONFIG_BT_NIMBLE_LEGACY_VHCI_ENABLE
 #define BLE_HS_HCI_FRAG_DATABUF_SIZE    \
     (BLE_ACL_MAX_PKT_SIZE +             \
@@ -403,6 +407,26 @@ ble_hs_hci_set_buf_sz(uint16_t pktlen, uint16_t max_pkts)
     return 0;
 }
 
+/**
+ * Returns the number of available ACL transmit buffers on the controller.
+ * This can be used by applications to throttle notification enqueuing.
+ */
+uint16_t
+ble_hs_hci_get_avail_pkts(void)
+{
+    if (!ble_hs_hci_initialized) {
+        return 0;
+    }
+
+    uint16_t avail_pkts;
+
+    ble_hs_lock_nested();
+    avail_pkts = ble_hs_hci_avail_pkts;
+    ble_hs_unlock_nested();
+
+    return avail_pkts;
+}
+
 /**
  * Increases the count of available controller ACL buffers.
  */
@@ -1084,6 +1108,7 @@ ble_hs_hci_init(void)
         goto err_mutex;
     }
 
+    ble_hs_hci_initialized = 1;
     return 0;
 
 err_mutex:
@@ -1102,6 +1127,7 @@ err:
         ble_hs_hci_ctx = NULL;
     }
 #endif
+    ble_hs_hci_initialized = 0;
     return rc;
 }
 
@@ -1109,6 +1135,8 @@ void ble_hs_hci_deinit(void)
 {
     int rc;
 
+    ble_hs_hci_initialized = 0;
+
 #if MYNEWT_VAL(BLE_STATIC_TO_DYNAMIC)
     if (ble_hs_hci_ctx == NULL) {
         return;

nimble/host/src/ble_hs_hci_priv.h

@@ -83,7 +83,13 @@ struct ble_hs_hci_sup_cmd {
     uint8_t commands[64];
 };
 
+uint16_t ble_hs_hci_get_avail_pkts(void);
+
+#if MYNEWT_VAL(BLE_STATIC_TO_DYNAMIC)
+#define ble_hs_hci_avail_pkts         (ble_hs_hci_get_avail_pkts())
+#else
 extern uint16_t ble_hs_hci_avail_pkts;
+#endif
 
 /* This function is not waiting for command status/complete HCI events */
 int ble_hs_hci_cmd_tx_no_rsp(uint16_t opcode, const void *cmd, uint8_t cmd_len);