component/bt: Add option to configure BLE SCA through menuconfig and use a fixed value of clock cycle to estimate sleep duration for external 32kHz oscillator

components/bt/Kconfig

@@ -161,23 +161,65 @@ menu Bluetooth
                 prompt "Bluetooth low power clock"
                 depends on BTDM_MODEM_SLEEP_MODE_ORIG
                 help
-                    Select the low power clock source for bluetooth controller
+                    Select the low power clock source for bluetooth controller. Bluetooth low power clock is
+                    the clock source to maintain time in sleep mode.
+
+                    - "Main crystal" option provides good accuracy and can support Dynamic Frequency Scaling
+                      to be used with Bluetooth modem sleep. Light sleep is not supported.
+                    - "External 32kHz crystal" option allows user to use a 32.768kHz crystal as Bluetooth low
+                      power clock. This option is allowed as long as External 32kHz crystal is configured as
+                      the system RTC clock source. This option provides good accuracy and supports Bluetooth
+                      modem sleep to be used alongside Dynamic Frequency Scaling or light sleep.
 
                 config BTDM_LPCLK_SEL_MAIN_XTAL
                     bool "Main crystal"
                     help
                         Main crystal can be used as low power clock for bluetooth modem sleep. If this option is
                         selected, bluetooth modem sleep can work under Dynamic Frequency Scaling(DFS) enabled, but
-                        cannot work when light sleep is enabled. Main crystal has a relatively better performance than
+                        cannot work when light sleep is enabled. Main crystal has a good performance in accuracy as
-                        other bluetooth low power clock sources.
+                        the bluetooth low power clock source.
 
                 config BTDM_LPCLK_SEL_EXT_32K_XTAL
                     bool "External 32kHz crystal"
                     depends on ESP32_RTC_CLK_SRC_EXT_CRYS
+                    help
+                        External 32kHz crystal has a nominal frequency of 32.768kHz and provides good frequency
+                        stability. If used as Bluetooth low power clock, External 32kHz can support Bluetooth
+                        modem sleep to be used with both DFS and light sleep.
             endchoice
 
         endmenu
 
+        choice BTDM_BLE_SLEEP_CLOCK_ACCURACY
+            prompt "BLE Sleep Clock Accuracy"
+            depends on BTDM_CTRL_MODE_BLE_ONLY || BTDM_CTRL_MODE_BTDM
+            default BTDM_BLE_DEFAULT_SCA_250PPM
+            help
+                BLE Sleep Clock Accuracy(SCA) for the local device is used to estimate window widening in BLE
+                connection events. With a lower level of clock accuracy(e.g. 500ppm over 250ppm), the slave
+                needs a larger RX window to synchronize with master in each anchor point, thus resulting in an
+                increase of power consumption but a higher level of robustness in keeping connected. According
+                to the requirements of Bluetooth Core specification 4.2, the worst-case accuracy of Classic
+                Bluetooth low power oscialltor(LPO) is +/-250ppm in STANDBY and in low power modes such as
+                sniff. For BLE the worst-case SCA is +/-500ppm.
+
+                - "151ppm to 250ppm" option is the default value for Bluetooth Dual mode
+                - "251ppm to 500ppm" option can be used in BLE only mode when using external 32kHz crystal as
+                   low power clock. This option is provided in case that BLE sleep clock has a lower level of
+                   accuracy, or other error sources contribute to the inaccurate timing during sleep.
+
+            config BTDM_BLE_DEFAULT_SCA_500PPM
+                bool "251ppm to 500ppm"
+                depends on BTDM_LPCLK_SEL_EXT_32K_XTAL && BTDM_CTRL_MODE_BLE_ONLY
+            config BTDM_BLE_DEFAULT_SCA_250PPM
+                bool "151ppm to 250ppm"
+        endchoice
+        config BTDM_BLE_SLEEP_CLOCK_ACCURACY_INDEX_EFF
+            int
+            default 0 if BTDM_BLE_DEFAULT_SCA_500PPM
+            default 1 if BTDM_BLE_DEFAULT_SCA_250PPM
+            default 1
+
         config BTDM_BLE_SCAN_DUPL
             bool "BLE Scan Duplicate Options"
             depends on (BTDM_CTRL_MODE_BTDM || BTDM_CTRL_MODE_BLE_ONLY)

components/bt/bt.c

@@ -1148,7 +1148,8 @@ esp_err_t esp_bt_controller_init(esp_bt_controller_config_t *cfg)
     set_div_ret = btdm_lpclk_set_div(0);
     assert(select_src_ret && set_div_ret);
     btdm_lpcycle_us_frac = RTC_CLK_CAL_FRACT;
-    btdm_lpcycle_us = esp_clk_slowclk_cal_get();
+    btdm_lpcycle_us = (RTC_CLK_CAL_FRACT > 15) ? (1000000 << (RTC_CLK_CAL_FRACT - 15)) :
+        (1000000 >> (15 - RTC_CLK_CAL_FRACT));
     assert(btdm_lpcycle_us != 0);
 #endif // CONFIG_BTDM_LPCLK_SEL_XX
     btdm_controller_set_sleep_mode(BTDM_MODEM_SLEEP_MODE_ORIG);

components/bt/include/esp_bt.h

@@ -37,6 +37,21 @@ typedef enum {
     ESP_BT_MODE_BTDM       = 0x03,   /*!< Run dual mode */
 } esp_bt_mode_t;
 
+/**
+ * @brief BLE sleep clock accuracy(SCA), values for ble_sca field in esp_bt_controller_config_t,
+ *        currently only ESP_BLE_SCA_500PPM and ESP_BLE_SCA_250PPM are supported
+ */
+enum {
+    ESP_BLE_SCA_500PPM     = 0,   /*!< BLE SCA at 500ppm */
+    ESP_BLE_SCA_250PPM,           /*!< BLE SCA at 250ppm */
+    ESP_BLE_SCA_150PPM,           /*!< BLE SCA at 150ppm */
+    ESP_BLE_SCA_100PPM,           /*!< BLE SCA at 100ppm */
+    ESP_BLE_SCA_75PPM,            /*!< BLE SCA at 75ppm */
+    ESP_BLE_SCA_50PPM,            /*!< BLE SCA at 50ppm */
+    ESP_BLE_SCA_30PPM,            /*!< BLE SCA at 30ppm */
+    ESP_BLE_SCA_20PPM,            /*!< BLE SCA at 20ppm */
+};
+
 #ifdef CONFIG_BT_ENABLED
 /* While scanning, if the free memory value in controller is less than SCAN_SEND_ADV_RESERVED_SIZE,
 the adv packet will be discarded until the memory is restored. */
@@ -106,15 +121,16 @@ the adv packet will be discarded until the memory is restored. */
     .hci_uart_no = BT_HCI_UART_NO_DEFAULT,                                 \
     .hci_uart_baudrate = BT_HCI_UART_BAUDRATE_DEFAULT,                     \
     .scan_duplicate_mode = SCAN_DUPLICATE_MODE,                            \
-    .scan_duplicate_type = SCAN_DUPLICATE_TYPE_VALUE,                     \
+    .scan_duplicate_type = SCAN_DUPLICATE_TYPE_VALUE,                      \
     .normal_adv_size = NORMAL_SCAN_DUPLICATE_CACHE_SIZE,                   \
     .mesh_adv_size = MESH_DUPLICATE_SCAN_CACHE_SIZE,                       \
     .send_adv_reserved_size = SCAN_SEND_ADV_RESERVED_SIZE,                 \
     .controller_debug_flag = CONTROLLER_ADV_LOST_DEBUG_BIT,                \
     .mode = BTDM_CONTROLLER_MODE_EFF,                                      \
-    .ble_max_conn = CONFIG_BTDM_CTRL_BLE_MAX_CONN_EFF,               \
+    .ble_max_conn = CONFIG_BTDM_CTRL_BLE_MAX_CONN_EFF,                     \
-    .bt_max_acl_conn = CONFIG_BTDM_CTRL_BR_EDR_MAX_ACL_CONN_EFF,     \
+    .bt_max_acl_conn = CONFIG_BTDM_CTRL_BR_EDR_MAX_ACL_CONN_EFF,           \
-    .bt_max_sync_conn = CONFIG_BTDM_CTRL_BR_EDR_MAX_SYNC_CONN_EFF,   \
+    .bt_max_sync_conn = CONFIG_BTDM_CTRL_BR_EDR_MAX_SYNC_CONN_EFF,         \
+    .ble_sca = CONFIG_BTDM_BLE_SLEEP_CLOCK_ACCURACY_INDEX_EFF,                  \
     .magic = ESP_BT_CONTROLLER_CONFIG_MAGIC_VAL,                           \
 };
 
@@ -150,6 +166,7 @@ typedef struct {
      * So, do not modify the value when esp_bt_controller_init()
      */
     uint8_t bt_max_sync_conn;               /*!< BR/EDR maximum ACL connection numbers. Effective in menuconfig */
+    uint8_t ble_sca;                        /*!< BLE low power crystal accuracy index */
     uint32_t magic;                         /*!< Magic number */
 } esp_bt_controller_config_t;