uart_ow: Initial support for Dallas 1-wire over UART support for MRAA

This commit introduces support for Dallas Semiconductor (DS) 1-wire
compliant device support using an available UART device.

The principle of operation is described in the following Application
note by Maxim Electronics:

https://www.maximintegrated.com/en/app-notes/index.mvp/id/214

with help (1-wire search) from:
https://www.maximintegrated.com/en/app-notes/index.mvp/id/187

It has been tested on Galileo 2 and Edison, with 2 DS 1-wire devices,
the DS18B20 and DS2413 connected to the bus.  A UPM driver for the
DS2413 is already complete and a PR will be submitted after this one.

It is important that you use a UART with CMOS/TTL level voltages
(3.3v/5v) RX and TX lines.  DO NOT use standard RS232 level voltages
or you are going to have a bad day.

In order for this to work, a simple interface circuit, using a single
diode must be constructed:

(forgive my "Asciihematic" :)

-|
U|
A| TX---|<--+
R|          |
T| RX-------o--------o 1-wire data bus
-|

The diode on TX is a 1N4148 (cheap and common), with the cathode
connected to TX, and the anode connected to RX and the 1-wire data
line.

The 1-wire data line requires a pull-up resistor, as the DS 1-wire
spec requires. 4.7-5K is typical for DS 1-wire buses.

NOTE: DHT-type (temp/humidity sensor) 1-wire devices ARE NOT DS 1-wire
compliant, and will not work with this code/circuit unfortunately.

Also note, this will use up one of your UARTs, which cannot be used
for any other purpose (ie: to access true UART-type serial devices).

You can however, connect as many DS 1-wire devices as feasible to this
UART, as it will function as a DS 1-wire bus master.

Signed-off-by: Jon Trulson <jtrulson@ics.com>
Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>

api/mraa/uart_ow.h

@@ -0,0 +1,189 @@
+/*
+ * Author: Jon Trulson <jtrulson@ics.com>
+ * Copyright (c) 2016 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#pragma once
+
+/**
+ * @file
+ * @brief UART OW module
+ *
+ * This module allows one to use MRAA's UART support in order to
+ * interact with Dallas 1-wire compliant devices on a 1-wire bus.  It
+ * makes use of the UART for timing purposes.  The principle of
+ * operation is described here:
+ * https://www.maximintegrated.com/en/app-notes/index.mvp/id/214
+ *
+ * It is important the you use a UART with CMOS/TTL level voltages
+ * (3.3v/5v) RX and TX lines.  DO NOT use standard RS232 level
+ * voltages, or you are going to have a bad day.
+ *
+ * In addition, a diode should be placed across the RX and
+ * TX lines like so:
+ *
+ * -|
+ * U|
+ * A| TX---|<--+
+ * R|          |
+ * T| RX-------o--------o 1-wire data bus
+ * -|
+ *
+ * The diode on TX is a 1N4148 (cheap and common), with the cathode
+ * connected to TX, and the anode connected to RX and the rest of the
+ * 1-wire data line.
+ *
+ * @snippet uart_ow.c Interesting
+ */
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <stdio.h>
+
+#include "common.h"
+
+/* for now, we simply use the normal MRAA UART context */
+typedef struct _uart* mraa_uart_ow_context;
+
+/* 8 bytes (64 bits) for a device rom code */
+static const int MRAA_UART_OW_ROMCODE_SIZE = 8;
+
+/**
+ * UART One Wire ROM related Command bytes
+ */
+typedef enum {
+    MRAA_UART_OW_CMD_READ_ROM = 0x33,         /**< read rom, when only one device on bus */
+    MRAA_UART_OW_CMD_MATCH_ROM = 0x55,        /**< match a specific rom code */
+    MRAA_UART_OW_CMD_SKIP_ROM = 0xcc,         /**< skip match/search rom */
+    MRAA_UART_OW_CMD_SEARCH_ROM_ALARM = 0xec, /**< search all roms in alarm state */
+    MRAA_UART_OW_CMD_SEARCH_ROM = 0xf0        /**< search all rom codes */
+} mraa_uart_ow_rom_cmd_t;
+
+/**
+ * Initialise uart_ow_context, uses UART board mapping
+ *
+ * @param uart the index of the uart set to use
+ * @return uart_ow context or NULL
+ */
+mraa_uart_ow_context mraa_uart_ow_init(int uart);
+
+/**
+ * Initialise a raw uart_ow_context. No board setup.
+ *
+ * @param path for example "/dev/ttyS0"
+ * @return uart_ow context or NULL
+ */
+mraa_uart_ow_context mraa_uart_ow_init_raw(const char* path);
+
+/**
+ * Get char pointer with tty device path within Linux
+ * For example. Could point to "/dev/ttyS0"
+ *
+ * @param dev uart_ow context
+ * @return char pointer of device path
+ */
+const char* mraa_uart_ow_get_dev_path(mraa_uart_ow_context dev);
+
+/**
+ * Destroy a mraa_uart_ow_context
+ *
+ * @param dev uart_ow context
+ * @return mraa_result_t
+ */
+mraa_result_t mraa_uart_ow_stop(mraa_uart_ow_context dev);
+
+/**
+ * Read a byte from the 1-wire bus
+ *
+ * @param dev uart_ow context
+ * @return the byte read
+ */
+uint8_t mraa_uart_ow_read_byte(mraa_uart_ow_context dev);
+
+/**
+ * Write a byte to a 1-wire bus
+ *
+ * @param dev uart_ow context
+ * @param byte the byte to write to the bus
+ * @return the byte read back during the time slot
+ */
+uint8_t mraa_uart_ow_write_byte(mraa_uart_ow_context dev, uint8_t byte);
+
+/**
+ * Write a bit to a 1-wire bus and read a bit corresponding to the
+ * time slot back.  This is possible due to the way we wired the TX
+ * and RX together with a diode, forming a loopback.
+ *
+ * @param dev uart_ow context
+ * @param bit the bit to write to the bus
+ * @return the bit read back during the time slot
+ */
+uint8_t mraa_uart_ow_bit(mraa_uart_ow_context dev, uint8_t bit);
+
+/**
+ * Send a reset pulse to the 1-wire bus and test for device presence
+ *
+ * @param dev uart_ow context
+ * @return one of the mraa_result_t values
+ */
+mraa_result_t mraa_uart_ow_reset(mraa_uart_ow_context dev);
+
+/**
+ * Begin a rom code search of the 1-wire bus.  This function
+ * implements the 1-wire search algorithm.  See the uart_ow.c example
+ * for an idea on how to use this function to identify all devices
+ * present on the bus.
+ *
+ * @param dev uart_ow context
+ * @param start true to start a new search from scratch, false to
+ * continue an existing search
+ * @param id the 8-byte rom code id of the current matched device when
+ * a device is found
+ * @return one of the mraa_result_t values
+ */
+mraa_result_t mraa_uart_ow_rom_search(mraa_uart_ow_context dev, mraa_boolean_t start, uint8_t* id);
+
+/**
+ * Send a command byte to a device on the 1-wire bus
+ *
+ * @param dev uart_ow context
+ * @param command the command byte to send
+ * @param id the rom code id of the device to receive the command,
+ * NULL for all devices on the bus
+ * @return one of the mraa_result_t values
+ */
+mraa_result_t mraa_uart_ow_command(mraa_uart_ow_context dev, uint8_t command, uint8_t* id);
+
+/**
+ * Perform a Dallas 1-wire compliant CRC8 computation on a buffer
+ *
+ * @param buffer the buffer containing the data
+ * @param length the length of the buffer
+ * @return the computed CRC
+ */
+uint8_t mraa_uart_ow_crc8(uint8_t* buffer, uint16_t length);
+
+#ifdef __cplusplus
+}
+#endif