Add bare-metal test for uart.

This test is for Vendors to check if uart (RawSerial) drivers are ready to use green-tea.

Example usage:
python test.py -t GCC_ARM -m NUCLEO_F070RB -b 9600 - run test using GCC_ARM toolchain, NUCLEO_F070RB board and test serial port with baud rate set to 9600 b/s.

Author: mprse

bare_metal_tests/.mbedignore

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+*

bare_metal_tests/uart/main.cpp

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+/* mbed Microcontroller Library
+ * Copyright (c) 2017 ARM Limited
+ *
+ * Licensed 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.
+ */
+#include "drivers/RawSerial.h"
+
+using namespace mbed;
+
+/* UART TEST FOR GREEN TEA
+ *
+ * Greentea-client uses RawSerial class to handle UART communication.
+ * RawSerial class must provide valid implementation of the following
+ * methods (used by Greentea-client):
+ *  - int RawSerial::getc()
+ *  - int RawSerial::putc(int c).
+ *
+ * Greentea-client uses USB serial port for communication with the
+ * following transmission parameters:
+ *  - 8 data bits,
+ *  - 1 stop bit,
+ *  - none parity bit,
+ *  - configurable baudrate.
+ *
+ * Greentea-client operates in pooling mode only.
+ * Flow control is disabled.
+ *
+ * UART buffer size is limited to 120 bytes.
+ *
+ * TEST SCENARIO
+ * This part of the test is executed on mbed board.
+ *
+ * After startup it will try to communicate via UART with host part of the test.
+ * This part sends 4 messages with different length to the host and waits
+ * for the response (host should respond with the same message).
+ * Last message "PASSED" is send to inform that all responses from host were
+ * successfully received.
+ *
+ * To perform this test with serial port baud rate different than default (9600),
+ * call host test with appropriate --baudrate parameter.
+ *
+ */
+
+/* Default baud rate if undefined. */
+#ifndef BAUD_RATE
+#define BAUD_RATE 9600
+#endif
+
+#define NUMBER_OF_TEST_STRINGS 5
+#define NUMBER_OF_TEST_RETRIES 10
+
+typedef enum
+{
+    PASSED, FAILED
+} test_status;
+
+/* Array of string to be transmitted. */
+const char *test_strings[NUMBER_OF_TEST_STRINGS] =
+        { "x",
+          "mbed", "Green Tea UART bare metal test.",
+          "Long Message-Long Message-Long Message-Long Message-Long Message-Long Message-Long Message-Long Message-Long Message--.",
+          "PASSED" };
+
+/* Function writes provided string to the serial port. */
+void write_line(RawSerial &serial, const char *str)
+{
+    while (true) {
+        serial.putc(*str);
+        if (*str == '\0') {
+            break;
+        }
+
+        str++;
+    };
+}
+
+/* Function reads provided string from the serial port. */
+int read_line(RawSerial &serial, char *buffer)
+{
+    int count = 0;
+    while (true) {
+        *buffer = (char) serial.getc();
+        count++;
+        if (*buffer == '\0') {
+            return count;
+        }
+
+        buffer += 1;
+    }
+}
+
+/* Function compares provided strings and returns 0 if are equal. */
+int strCmp(const char string1[], char string2[])
+{
+    for (int i = 0;; i++) {
+        if (string1[i] != string2[i]) {
+            return string1[i] < string2[i] ? -1 : 1;
+        }
+
+        if (string1[i] == '\0') {
+            return 0;
+        }
+    }
+}
+
+/* Function writes provided message to the serial port and
+ * waits for the response from the Host. Host should
+ * respond with the same message.
+ *
+ * If valid response has been received, then function returns
+ * PASSED status, otherwise transmission is repeated.
+ *
+ * If max number of transmission attempts is reached, then
+ * function returns FAILED status.
+ *
+ * */
+test_status test_uart_communication(RawSerial &serial, const char * msg)
+{
+    char buffer[120];
+
+    for (int i = 0; i < NUMBER_OF_TEST_RETRIES; i++) {
+        write_line(serial, msg);
+        read_line(serial, buffer);
+
+        if (strCmp(msg, buffer) == 0) {
+            return PASSED;
+        }
+    }
+
+    return FAILED;
+}
+
+int main()
+{
+    RawSerial serial(USBTX, USBRX, BAUD_RATE);
+
+    /* Start the test. */
+    for (unsigned int i = 0; i < (sizeof(test_strings) / sizeof(test_strings[0])); i++) {
+        if (test_uart_communication(serial, test_strings[i]) == FAILED) {
+            break;
+        }
+    }
+
+    while (true);
+}
+