diff --git a/components/bt/host/nimble/Kconfig.in b/components/bt/host/nimble/Kconfig.in
index c469323ba81..bcfe46d2be0 100644
--- a/components/bt/host/nimble/Kconfig.in
+++ b/components/bt/host/nimble/Kconfig.in
@@ -105,6 +105,15 @@ config BT_NIMBLE_DEBUG
     help
         This enables extra runtime asserts and host debugging
 
+config BT_NIMBLE_SM_SC_DEBUG_KEYS
+    bool "Use predefined public-private key pair"
+    default n
+    depends on BT_NIMBLE_SM_SC
+    help
+        If this option is enabled, SM uses predefined DH key pair as described
+        in Core Specification, Vol. 3, Part H, 2.3.5.6.1. This allows to
+        decrypt air traffic easily and thus should only be used for debugging.
+
 config BT_NIMBLE_SVC_GAP_DEVICE_NAME
     string "BLE GAP default device name"
     depends on BT_NIMBLE_ENABLED
diff --git a/components/bt/host/nimble/esp-hci/src/esp_nimble_hci.c b/components/bt/host/nimble/esp-hci/src/esp_nimble_hci.c
index 545334e9202..3c9c81790ca 100644
--- a/components/bt/host/nimble/esp-hci/src/esp_nimble_hci.c
+++ b/components/bt/host/nimble/esp-hci/src/esp_nimble_hci.c
@@ -66,6 +66,8 @@ static os_membuf_t ble_hci_evt_lo_buf[
                     MYNEWT_VAL(BLE_HCI_EVT_BUF_SIZE))
 ];
 
+const static char *TAG = "NimBLE";
+
 void ble_hci_trans_cfg_hs(ble_hci_trans_rx_cmd_fn *cmd_cb,
                      void *cmd_arg,
                      ble_hci_trans_rx_acl_fn *acl_cb,
@@ -85,7 +87,9 @@ int ble_hci_trans_hs_cmd_tx(uint8_t *cmd)
     assert(cmd != NULL);
     *cmd = BLE_HCI_UART_H4_CMD;
     len = BLE_HCI_CMD_HDR_LEN + cmd[3] + 1;
-    while (!esp_vhci_host_check_send_available()) {
+    if (!esp_vhci_host_check_send_available()) {
+        ESP_LOGE(TAG, "Controller not ready to receive packets from host at this time, try again after sometime");
+        return BLE_HS_EAGAIN;
     }
     esp_vhci_host_send_packet(cmd, len);
 
@@ -115,8 +119,9 @@ int ble_hci_trans_hs_acl_tx(struct os_mbuf *om)
     data[0] = BLE_HCI_UART_H4_ACL;
     len++;
 
-    while (!esp_vhci_host_check_send_available()) {
-        vTaskDelay(1000 / portTICK_PERIOD_MS);
+    if (!esp_vhci_host_check_send_available()) {
+        ESP_LOGE(TAG, "Controller not ready to receive packets from host at this time, try again after sometime");
+        return BLE_HS_EAGAIN;
     }
 
     os_mbuf_copydata(om, 0, OS_MBUF_PKTLEN(om), &data[1]);
diff --git a/components/bt/host/nimble/nimble b/components/bt/host/nimble/nimble
index 6c91a9a153c..5f6348d0ddd 160000
--- a/components/bt/host/nimble/nimble
+++ b/components/bt/host/nimble/nimble
@@ -1 +1 @@
-Subproject commit 6c91a9a153c421231b686d30c822e53fea7510c0
+Subproject commit 5f6348d0ddd7f98841e458bbc808e8f7f5f23b23
diff --git a/components/bt/host/nimble/port/include/esp_nimble_cfg.h b/components/bt/host/nimble/port/include/esp_nimble_cfg.h
index c0b329c465a..9cd59415f68 100644
--- a/components/bt/host/nimble/port/include/esp_nimble_cfg.h
+++ b/components/bt/host/nimble/port/include/esp_nimble_cfg.h
@@ -423,6 +423,14 @@
 #endif
 #endif
 
+#ifndef MYNEWT_VAL_BLE_SM_SC_DEBUG_KEYS
+#ifdef CONFIG_BT_NIMBLE_SM_SC_DEBUG_KEYS
+#define MYNEWT_VAL_BLE_SM_SC_DEBUG_KEYS (1)
+#else
+#define MYNEWT_VAL_BLE_SM_SC_DEBUG_KEYS (0)
+#endif
+#endif
+
 #ifndef MYNEWT_VAL_BLE_HS_AUTO_START
 #define MYNEWT_VAL_BLE_HS_AUTO_START (1)
 #endif