1. modify i2c_set_pin function

2. update example comments and other minor changes
3. rename API:  i2c_cmd_link_create/i2c_cmd_link_delete (+4 squashed commits)

Squashed commits:
[2e0ac3e] 1. coding style: add one space after condition key words.
2. modify i2c.h, use gpio_num_t instead of int, improve comments of return values
3. add i2c index in index.rst
4. add readme for i2c example
[4991d92] update i2c.doc
[88b672e] driver: i2c

1. add mux and spin lock to run in a thread-safe way.
2. modify example code
[4eb15fe] driver: i2c code

1. add i2c master code
2. add i2c slave code
3. add i2c example code
4. add DRAM_ATTR for I2C array

components/esp32/include/soc/i2c_reg.h

@@ -261,6 +261,8 @@
 #define I2C_RXFIFO_FULL_THRHD_V  0x1F
 #define I2C_RXFIFO_FULL_THRHD_S  0
 
+#define I2C_DATA_APB_REG(i)      (0x60013000 + (i) * 0x14000 + 0x001c)
+
 #define I2C_DATA_REG(i)          (REG_I2C_BASE(i) + 0x001c)
 /* I2C_FIFO_RDATA : RO ;bitpos:[7:0] ;default: 8'b0 ; */
 /*description: The register represent the byte  data read from rxfifo when use apb fifo access*/

components/esp32/include/soc/i2c_struct.h

@@ -16,7 +16,7 @@
 typedef volatile struct {
     union {
         struct {
-            uint32_t scl_low_period:14;             /*This register is used to configure the  low level width of SCL clock.*/
+            uint32_t period:14;             /*This register is used to configure the  low level width of SCL clock.*/
             uint32_t reserved14:    18;
         };
         uint32_t val;
@@ -58,7 +58,7 @@ typedef volatile struct {
     } status_reg;
     union {
         struct {
-            uint32_t tout:      20;                 /*This register is used to configure the max clock number of receiving  a data.*/
+            uint32_t tout:      20;                 /*This register is used to configure the max clock number of receiving a data, unit: APB clock cycle.*/
             uint32_t reserved20:12;
         };
         uint32_t val;
@@ -282,7 +282,7 @@ typedef volatile struct {
     uint32_t reserved_f4;
     uint32_t date;                                  /**/
     uint32_t reserved_fc;
-    uint32_t fifo_start_addr;                       /*This the start address for ram when use apb nonfifo access.*/
+    uint32_t ram_data[32];                          /*This the start address for ram when use apb nonfifo access.*/
 } i2c_dev_t;
 extern i2c_dev_t I2C0;
 extern i2c_dev_t I2C1;

docs/api/i2c.rst

@@ -0,0 +1,82 @@
+I2C
+===========
+
+Overview
+--------
+
+ESP32 has two I2C controllers which can be set as master mode or slave mode.
+
+Application Example
+-------------------
+
+I2C master and slave example: `examples/18_i2c <https://github.com/espressif/esp-idf/tree/master/examples/18_i2c>`_.
+
+API Reference
+-------------
+
+Header Files
+^^^^^^^^^^^^
+
+  * `driver/include/driver/i2c.h <https://github.com/espressif/esp-idf/blob/master/components/driver/include/driver/i2c.h>`_
+
+Macros
+^^^^^^
+
+.. doxygendefine:: I2C_APB_CLK_FREQ
+.. doxygendefine:: I2C_FIFO_LEN
+
+Type Definitions
+^^^^^^^^^^^^^^^^
+
+.. doxygentypedef:: i2c_cmd_handle_t
+
+Enumerations
+^^^^^^^^^^^^
+
+.. doxygenenum:: i2c_mode_t
+.. doxygenenum:: i2c_rw_t
+.. doxygenenum:: i2c_trans_mode_t
+.. doxygenenum:: i2c_opmode_t
+.. doxygenenum:: i2c_port_t
+.. doxygenenum:: i2c_addr_mode_t
+
+Structures
+^^^^^^^^^^
+
+.. doxygenstruct:: i2c_config_t
+    :members:
+
+
+Functions
+^^^^^^^^^
+
+.. doxygenfunction:: i2c_driver_install
+.. doxygenfunction:: i2c_driver_delete
+.. doxygenfunction:: i2c_param_config
+.. doxygenfunction:: i2c_reset_tx_fifo
+.. doxygenfunction:: i2c_reset_rx_fifo
+.. doxygenfunction:: i2c_isr_register
+.. doxygenfunction:: i2c_isr_free
+.. doxygenfunction:: i2c_set_pin
+.. doxygenfunction:: i2c_master_start
+.. doxygenfunction:: i2c_master_write_byte
+.. doxygenfunction:: i2c_master_write
+.. doxygenfunction:: i2c_master_read_byte
+.. doxygenfunction:: i2c_master_read
+.. doxygenfunction:: i2c_master_stop
+.. doxygenfunction:: i2c_master_cmd_begin
+.. doxygenfunction:: i2c_slave_write_buffer
+.. doxygenfunction:: i2c_slave_read
+.. doxygenfunction:: i2c_set_period
+.. doxygenfunction:: i2s_get_period
+.. doxygenfunction:: i2c_set_start_timing
+.. doxygenfunction:: i2c_get_start_timing
+.. doxygenfunction:: i2c_set_stop_timing
+.. doxygenfunction:: i2c_get_stop_timing
+.. doxygenfunction:: i2c_set_data_timing
+.. doxygenfunction:: i2c_get_data_timing
+.. doxygenfunction:: i2c_set_data_mode
+.. doxygenfunction:: i2c_get_data_mode
+.. doxygenfunction:: i2c_cmd_link_create
+.. doxygenfunction:: i2c_cmd_link_delete
+

docs/index.rst

@@ -107,6 +107,7 @@ Contents:
    LED Control <api/ledc>
    Remote Control <api/rmt>
    Timer <api/timer>
+   I2C <api/i2c>
    Pulse Counter <api/pcnt>
    Sigma-delta Modulation <api/sigmadelta>
    SPI Flash and Partition APIs <api/spi_flash>

examples/18_i2c/Makefile

@@ -0,0 +1,9 @@
+#
+# This is a project Makefile. It is assumed the directory this Makefile resides in is a
+# project subdirectory.
+#
+
+PROJECT_NAME := i2c
+
+include $(IDF_PATH)/make/project.mk
+

examples/18_i2c/README.md

@@ -0,0 +1,29 @@
+# I2C Example
+
+
+* This example will show you how to use I2C module by running two tasks on i2c bus:
+
+    * read external i2c sensor, here we use a BH1750 light sensor(GY-30 module) for instance.
+    * Use one I2C port(master mode) to read or write the other I2C port(slave mode) on one ESP32 chip.
+
+* Pin assignment:
+
+    * slave :
+        * GPIO25 is assigned as the data signal of i2c slave port
+        * GPIO26 is assigned as the clock signal of i2c slave port
+    * master:
+        * GPIO18 is assigned as the data signal of i2c master port
+        * GPIO19 is assigned as the clock signal of i2c master port
+
+* Connection:
+
+    * connect GPIO18 with GPIO25
+    * connect GPIO19 with GPIO26
+    * connect sda/scl of sensor with GPIO18/GPIO19
+    * no need to add external pull-up resistors, driver will enable internal pull-up resistors.
+
+* Test items:
+
+    * read the sensor data, if connected.
+    * i2c master(ESP32) will write data to i2c slave(ESP32).
+    * i2c master(ESP32) will read data from i2c slave(ESP32).

examples/18_i2c/main/component.mk

@@ -0,0 +1,3 @@
+#
+# Main Makefile. This is basically the same as a component makefile.
+#