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>

examples/c++/CMakeLists.txt

@@ -8,6 +8,7 @@ add_executable (Spi-pot Spi-pot.cpp)
 add_executable (Uart Uart-example.cpp)
 add_executable (Isr-pin6 Isr-pin6.cpp)
 add_executable (Iio-dummy Iio-dummy.cpp)
+add_executable (UartOW UartOW.cpp)
 
 include_directories(${PROJECT_SOURCE_DIR}/api)
 
@@ -19,3 +20,4 @@ target_link_libraries (Spi-pot mraa stdc++)
 target_link_libraries (Uart mraa stdc++)
 target_link_libraries (Isr-pin6 mraa stdc++)
 target_link_libraries (Iio-dummy mraa stdc++)
+target_link_libraries (UartOW mraa stdc++)

examples/c++/UartOW.cpp

@@ -0,0 +1,82 @@
+/*
+ * 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.
+ */
+
+#include "stdio.h"
+#include "iostream"
+//! [Interesting]
+#include "uart_ow.hpp"
+
+using namespace std;
+
+int
+main(int argc, char** argv)
+{
+    mraa::UartOW* uart = new mraa::UartOW(0);
+
+    // Reset the ow bus and see if anything is present
+    mraa::Result rv;
+
+    if ((rv = uart->reset()) == mraa::SUCCESS) {
+        cout << "Reset succeeded, device(s) detected!" << endl;
+    } else {
+        cout << "Reset failed, returned " << int(rv) << ". No devices on bus?" << endl;
+        return 1;
+    }
+
+    cout << "Looking for devices..." << endl;
+    ;
+
+    uint8_t count = 0;
+    // start the search from scratch
+    string id = uart->search(true);
+
+    if (id.empty()) {
+        cout << "No devices detected." << endl;
+        return 1;
+    }
+
+    while (!id.empty()) {
+        // hack so we don't need to cast each element of the romcode
+        // for printf purposes
+        uint8_t* ptr = (uint8_t*) id.c_str();
+
+        // The first byte (0) is the device type (family) code.
+        // The last byte (7) is the rom code CRC value.  The
+        // intervening bytes are the unique 48 bit device ID.
+
+        printf("Device %02d Type 0x%02x ID %02x%02x%02x%02x%02x%02x CRC 0x%02x\n", count, ptr[0],
+               ptr[6], ptr[5], ptr[4], ptr[3], ptr[2], ptr[1], ptr[7]);
+        count++;
+
+        // continue the search with start argument set to false
+        id = uart->search(false);
+    }
+
+    cout << "Exiting..." << endl;
+
+    delete uart;
+
+    return 0;
+}
+//! [Interesting]