add Chapter 15 - runtime observer implementation

Chapter15/observer/cstdlib_support/retarget.cpp

@@ -0,0 +1,81 @@
+#include <retarget.hpp>
+
+#include <errno.h>
+#include <stdio.h>
+#include <sys/stat.h>
+
+#include <span>
+
+namespace 
+{
+hal::uart *uart_stdio;
+};
+
+void retarget::set_stdio_uart(hal::uart *uart)
+{
+    uart_stdio = uart;
+
+    /* Disable I/O buffering for STDOUT stream, so that
+    * chars are sent out as soon as they are printed. */
+    setvbuf(stdout, NULL, _IONBF, 0);
+}
+
+#define STDIN_FILENO 0
+#define STDOUT_FILENO 1
+#define STDERR_FILENO 2
+
+extern "C" int _write(int fd, char * ptr, int len)
+{
+    if(fd == STDOUT_FILENO || fd == STDERR_FILENO)
+    {
+        uart_stdio->write(std::span<const char>(ptr, len));
+    }
+
+    return len;
+}
+
+extern "C" int _isatty(int fd)
+{
+    if(fd >= STDIN_FILENO && fd <= STDERR_FILENO)
+    {
+        return 1;
+    }
+    errno = EBADF;
+    return 0;
+}
+
+extern "C" int _close(int fd)
+{
+        if(fd >= STDIN_FILENO && fd <= STDERR_FILENO)
+                return 0;
+
+        errno = EBADF;
+        return -1;
+}
+
+extern "C" int _lseek(int fd, int ptr, int dir)
+{
+        (void)fd;
+        (void)ptr;
+        (void)dir;
+
+        errno = EBADF;
+        return -1;
+}
+
+extern "C" int _read(int fd, char *ptr, int len)
+{
+    return -1;
+}
+
+int _fstat(int fd, struct stat *st)
+{
+        if(fd >= STDIN_FILENO && fd <= STDERR_FILENO)
+        {
+                st->st_mode = S_IFCHR;
+                return 0;
+        }
+
+        errno = EBADF;
+        return 0;
+}

Chapter15/observer/cstdlib_support/retarget.hpp

@@ -0,0 +1,10 @@
+#pragma once
+
+#include <uart.hpp>
+
+namespace retarget 
+{
+
+void set_stdio_uart(hal::uart *uart);
+
+};