Optimize configuration of base MAC address

Application developer can call APIs to configure base MAC address
    instead of using menuconfig.

docs/api-reference/system/base_mac_address.rst

@@ -0,0 +1,77 @@
+Base MAC address
+================
+
+Overview
+--------
+
+Serveral universally administered(by IEEE) MAC addresses are uniquely assigned to the networking interfaces(WiFi/BT/Ethernet). 
+The final octet of each universally administered MAC address increases by one. Only the first one which is called base MAC address 
+of them is stored in EFUSE or external storage, the others are generated from it. Here, 'generate' means adding 0, 1, 2 and 3 
+(respectively) to the final octet of the base MAC address. 
+
+If the universally administered MAC addresses are not enough for all of the networking interfaces. Local administered MAC addresses
+which are derived from universally administered MAC addresses are assigned to the reset of networking interfaces. 
+
+A `definition of local vs universal MAC address can be found on Wikipedia<https://en.wikipedia.org/wiki/MAC_address#Universal_vs._local>`.
+
+The number of universally administered MAC address can be configured using ``make menuconfig``.
+
+Base MAC address
+^^^^^^^^^^^^^^^^
+
+If using the default base MAC address factory programmed by Espressif in BLK0 of EFUSE, nothing needs to be done.
+
+If using a custom base MAC address stored in BLK3 of EFUSE, call API esp_efuse_mac_get_custom() to get the base MAC address
+which is stored in BLK3 of EFUSE. If correct MAC address is returned, then call esp_base_mac_addr_set() to set the base MAC 
+address for system to generate the MAC addresses used by the networking interfaces(WiFi/BT/Ethernet).
+There are 192 bits storage spaces for custom to store base MAC address in BLK3 of EFUSE. They are EFUSE_BLK3_RDATA0, 
+EFUSE_BLK3_RDATA1, EFUSE_BLK3_RDATA2, EFUSE_BLK3_RDATA3, EFUSE_BLK3_RDATA4 and EFUSE_BLK3_RDATA5, each of them is 32 bits 
+register. The format of the 192 bits storage spaces is:
+------------------------------------------------------
+Field       |Bits |Range     |Description
+------------------------------------------------------
+version     |8    |[191:184] |1: useful. 0: useless
+------------------------------------------------------
+reserve     |112  |[183:72]  |reserved
+------------------------------------------------------
+mac address |64   |[71:8]    |base MAC address
+------------------------------------------------------
+mac crc     |8    |[7:0]     |crc of base MAC address
+------------------------------------------------------
+
+If using base MAC address stored in external storage, firstly get the base MAC address stored in external storage, then call 
+API esp_base_mac_addr_set() to set the base MAC address for system to generate the MAC addresses used by the networking 
+interfaces(WiFi/BT/Ethernet).
+
+All of the steps must be done before initializing the networking interfaces(WiFi/BT/Ethernet). It is recommended to do it in 
+app_main() which can be referenced in example `system/base_mac_address`.
+
+Number of universally administered MAC address
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+If the number of universal MAC addresses is two, only two interfaces (WiFi station and Bluetooth) receive a universally 
+administered MAC address. These are generated sequentially by adding 0 and 1 (respectively) to the base MAC address. 
+The remaining two interfaces (WiFi softap and Ethernet) receive local MAC addresses. These are derived from the universal 
+WiFi station and Bluetooth MAC addresses, respectively.
+
+If the number of universal MAC addresses is four, all four interfaces (WiFi station, WiFi softap, Bluetooth and Ethernet) 
+receive a universally administered MAC address. These are generated sequentially by adding 0, 1, 2 and 3 (respectively) 
+to the final octet of the base MAC address.
+
+When using the default (Espressif-assigned) base MAC address, either setting can be used. When using a custom universal MAC 
+address range, the correct setting will depend on the allocation of MAC addresses in this range (either 2 or 4 per device.)
+        
+API Reference
+-------------
+
+Header Files
+^^^^^^^^^^^^
+
+  * :component_file:`esp32/include/esp_system.h`
+
+
+Functions
+---------
+
+.. doxygenfunction:: esp_base_mac_addr_set
+.. doxygenfunction:: esp_efuse_mac_get_custom

docs/api-reference/system/index.rst

@@ -10,6 +10,7 @@ System API
    Over The Air Updates (OTA) <ota>
    Deep Sleep <deep_sleep>
    Logging <log>
+   Base MAC address <base_mac_address>
 
 
 Example code for this API section is provided in :example:`system` directory of ESP-IDF examples.