zephyr: Add zephyr_getchar module to handle console input.

From https://github.com/pfalcon/zephyr_getchar .

zephyr/src/zephyr_getchar.c

+/*
+ * Copyright (c) 2016 Linaro
+ *
+ * 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 <zephyr.h>
+#include <uart.h>
+#include <drivers/console/uart_console.h>
+#include <misc/printk.h>
+#include "zephyr_getchar.h"
+
+static struct nano_sem uart_sem;
+#define UART_BUFSIZE 256
+static uint8_t uart_ringbuf[UART_BUFSIZE];
+static uint8_t i_get, i_put;
+
+static int console_irq_input_hook(struct device *dev, uint8_t ch)
+{
+    int i_next = (i_put + 1) & (UART_BUFSIZE - 1);
+    if (i_next == i_get) {
+        printk("UART buffer overflow - char dropped\n");
+        return 1;
+    }
+    uart_ringbuf[i_put] = ch;
+    i_put = i_next;
+    //printk("%x\n", ch);
+    nano_isr_sem_give(&uart_sem);
+    return 1;
+}
+
+uint8_t zephyr_getchar(void) {
+    nano_task_sem_take(&uart_sem, TICKS_UNLIMITED);
+    unsigned int key = irq_lock();
+    uint8_t c = uart_ringbuf[i_get++];
+    i_get &= UART_BUFSIZE - 1;
+    irq_unlock(key);
+    return c;
+}
+
+void zephyr_getchar_init(void) {
+    nano_sem_init(&uart_sem);
+    struct device *uart_console_dev = device_get_binding(CONFIG_UART_CONSOLE_ON_DEV_NAME);
+    uart_irq_input_hook_set(uart_console_dev, console_irq_input_hook);
+    // All NULLs because we're interested only in the callback above
+    uart_register_input(NULL, NULL, NULL);
+}

zephyr/src/zephyr_getchar.h

+/*
+ * Copyright (c) 2016 Linaro
+ *
+ * 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 <stdint.h>
+
+void zephyr_getchar_init(void);
+uint8_t zephyr_getchar(void);