extras/softuart: add initial port

This is a initial port of esp8266-software-uart [1] and for now
it only supports one RX port with 8n1.

1 https://github.com/plieningerweb/esp8266-software-uart

extras/softuart/softuart.h

@@ -0,0 +1,87 @@
+/*
+ * Softuart for esp-open-rtos
+ *
+ * Copyright (C) 2016 Bernhard Guillon <Bernhard.Guillon@web.de>
+ *
+ * This code is based on Softuart from here [1] and reworked to
+ * fit into esp-open-rtos. For now only the RX part is ported.
+ * Also the configuration of the pin is for now hardcoded.
+ *
+ * it fits my needs to read the GY-GPS6MV2 module with 9600 8n1
+ *
+ * Original Copyright:
+ * Copyright (c) 2015 plieningerweb
+ *
+ * MIT Licensed as described in the file LICENSE
+ *
+ * 1 https://github.com/plieningerweb/esp8266-software-uart
+ */
+#ifndef SOFTUART_H_
+#define SOFTUART_H_
+
+#include <stdint.h>
+#include <stdbool.h>
+
+#ifdef __cplusplus
+extern "C"
+{
+#endif
+
+// FIXME: for now you need to provide the gpio number for RX here
+#define rx_pin 13
+
+#define SOFTUART_MAX_RX_BUFF 64
+#define SOFTUART_GPIO_COUNT 16
+
+/**
+ * Private data buffer
+ */
+typedef struct softuart_buffer_t
+{
+    char receive_buffer[SOFTUART_MAX_RX_BUFF];
+    uint8_t receive_buffer_tail;
+    uint8_t receive_buffer_head;
+    uint8_t buffer_overflow;
+} softuart_buffer_t;
+
+/**
+ * Private softuart descriptor
+ */
+typedef struct
+{
+    uint8_t pin_rx;                    //!< This value is ignored by now but planned to get added again
+    volatile softuart_buffer_t buffer; //!< Internal buffer
+    uint16_t bit_time;                 //!< Time for one bit, filled by softuart
+} softuart;
+
+/**
+ * Initialize software uart and setup interrup handlers
+ *
+ * FIXME: For now you will have to set up the
+ *        rx_pin and handle_rx your self.
+ *
+ * @param baudrate actual baudrate
+ * @return true if no errors occured otherwise false
+ */
+bool softuart_init(uint32_t baudrate);
+
+/**
+ * Check if data is available
+ * @return true if data is available otherwise false
+ */
+bool softuart_available();
+
+/**
+ * Read current byte from internal buffer if available.
+ *
+ * NOTE: This call is non blocking.
+ * NOTE: You have to check softuart_available first.
+ * @return current byte
+ */
+uint8_t softuart_read();
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* SOFTUART_H_ */