Add implementation of stdio.

src/app/gps-stdio.c

+/*
+
+Implement stdio and fetch GPS data.
+
+Copyright (C) 2019, ENSIMAG students
+This project is under the MIT license
+
+*/
+
+#include <mutex.h>
+
+#include <stdio.h>
+
+
+typedef struct {
+    mutex_t mutex = MUTEX_INIT;
+} gps_isr_info_t;
+
+static gps_isr_info_t gps_isr_info;
+
+
+// Handle 
+static void gps_isr(gps_isr_info_t *info, char c)
+{
+    mutex_unlock(&info->mutex);
+}
+
+
+// STDIN is disabled in our application.
+ssize_t stdio_read(void *buffer, size_t count)
+{
+    return 0;
+}
+
+// Write STDOUT data to serial port 0.
+ssize_t stdio_write(const void *buffer, size_t len)
+{
+    uart_write(STDIO_UART_DEV, (const uint8_t *)buffer, len);
+    return len;
+}
+
+// Initialize STDIO module.
+void stdio_init(void)
+{
+    uart_init(STDIO_UART_DEV, STDIO_UART_BAUDRATE, (uart_rx_cb_t)gps_isr, &gps_isr_info);
+}

src/app/gps.c

-/*
-
-Fetch GPS data.
-
-Copyright (C) 2019, ENSIMAG students
-This project is under the MIT license
-
-*/
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