drivers: add generic i2c bitbang driver

drivers/i2c/Kconfig

@@ -38,6 +38,47 @@ config I2C_NTRACE
 	default 32
 	depends on I2C_TRACE
 
+config I2C_BITBANG
+	bool "I2C bitbang implementation"
+	default n
+	---help---
+		Enable support for a bitbang implementation of I2C
+
+if I2C_BITBANG
+
+  config I2C_BITBANG_NO_DELAY
+  bool "Do not add delay"
+  default n
+  ---help---
+    If you want to go full speed (depending on how fast pins can be toggled)
+    you can enable this option. This will not respect the desired frequency
+    set during the I2C transfer operation.
+
+  config I2C_BITBANG_GPIO_OVERHEAD
+	int "GPIO overhead"
+	depends on !I2C_BITBANG_NO_DELAY
+	default 0
+	---help---
+		Overhead of GPIO toggling operation to consider when computing
+		delays. This overhead will be subtracted from sleep times to achieve
+		desired frquency.
+
+	config I2C_BITBANG_TIMEOUT
+	int "I2C timeout"
+	default 1000
+	---help---
+		Timeout (microseconds) to abort wait on slave
+
+	config I2C_BITBANG_CLOCK_STRETCHING
+	bool "Support clock stretching"
+	default n
+	---help---
+		This enables I2C clock stretching. This requires the hardware to set
+		the pin into open-collector mode (master sets SCL high and waits until
+		slave stops holding it low).
+
+endif # I2C_BITBANG
+
 config I2C_DRIVER
 	bool "I2C character driver"
 	default n

drivers/i2c/Make.defs

@@ -44,6 +44,10 @@ ifeq ($(CONFIG_I2C_DRIVER),y)
 CSRCS += i2c_driver.c
 endif
 
+ifeq ($(CONFIG_I2C_BITBANG),y)
+CSRCS += i2c_bitbang.c
+endif
+
 # Include the selected I2C multiplexer drivers
 
 ifeq ($(CONFIG_I2CMULTIPLEXER_PCA9540BDP),y)

include/nuttx/i2c/i2c_bitbang.h

@@ -0,0 +1,82 @@
+/****************************************************************************
+ * drivers/i2c/i2c_bitbang.h
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.  The
+ * ASF licenses this file to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the
+ * License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ *
+ ****************************************************************************/
+
+#ifndef __DRIVERS_I2C_I2C_BITBANG_H
+#define __DRIVERS_I2C_I2C_BITBANG_H
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+#include <nuttx/i2c/i2c_master.h>
+#include <stdbool.h>
+
+/****************************************************************************
+ * Public Types
+ ****************************************************************************/
+
+struct i2c_bitbang_lower_dev_s;
+
+struct i2c_bitbang_lower_ops_s
+{
+  /* Initialize pins to appropriate state (usually open-drain) */
+
+  CODE void (*initialize)(FAR struct i2c_bitbang_lower_dev_s *lower);
+
+  /* Set high/low level for SCL/SDA pins */
+
+  CODE void (*set_scl)(FAR struct i2c_bitbang_lower_dev_s *lower, bool high);
+  CODE void (*set_sda)(FAR struct i2c_bitbang_lower_dev_s *lower, bool high);
+
+  /* Read level of SCL/SDA pins */
+
+  CODE bool (*get_scl)(FAR struct i2c_bitbang_lower_dev_s *lower);
+  CODE bool (*get_sda)(FAR struct i2c_bitbang_lower_dev_s *lower);
+};
+
+struct i2c_bitbang_lower_dev_s
+{
+  FAR const struct i2c_bitbang_lower_ops_s *ops;
+  FAR void *priv;
+};
+
+/****************************************************************************
+ * Public Function Prototypes
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: i2c_bitbang_initialize
+ *
+ * Description:
+ *   Initialize a bitbang I2C device instance
+ *
+ * Input Parameters:
+ *   lower  - Lower half of driver
+ *
+ * Returned Value:
+ *   Pointer to a the I2C instance
+ *
+ ****************************************************************************/
+
+FAR struct i2c_master_s *i2c_bitbang_initialize(
+    FAR struct i2c_bitbang_lower_dev_s *lower);
+
+#endif /* __DRIVERS_I2C_I2C_BITBANG_H */