mbed_retarget: Add an internal class to provide basic console functionality

The retarget code allocates an array of FileHandle* for console and file
handling (filehandles). A tiny target only needs a console (putc/getc).
There is no need for file handling.

The POSIX layer and the array of FileHandle* is not required for small
targets that only need a console ; this code is optionally compiled
out if the configuration parameter platform.stdio-minimal-console-only is
set to `"true"`.

Author: hugueskamba

platform/mbed_lib.json

@@ -12,7 +12,12 @@
         },
 
         "stdio-buffered-serial": {
-            "help": "(Applies if target.console-uart is true.) Use UARTSerial driver to obtain buffered serial I/O on stdin/stdout/stderr. If false, unbuffered serial_getc and serial_putc are used directly.",
+            "help": "(Applies if target.console-uart is true and stdio-minimal-console-only is false.) Use UARTSerial driver to obtain buffered serial I/O on stdin/stdout/stderr. If false, unbuffered serial_getc and serial_putc are used directly.",
+            "value": false
+        },
+
+        "stdio-minimal-console-only": {
+            "help": "(Ignores stdio-buffered-serial) Creates a console for basic unbuffered I/O operations. Enable if your application does not require file handles to access the serial interface. The POSIX `fsync` function will always an error.",
             "value": false
         },
 

platform/mbed_retarget.h

@@ -91,9 +91,11 @@ typedef unsigned int  gid_t;    ///< Group ID
 #if __cplusplus
 namespace mbed {
 
+
 class FileHandle;
 class DirHandle;
 
+#if !MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
 /** Targets may implement this to change stdin, stdout, stderr.
  *
  * If the application hasn't provided mbed_override_console, this is called
@@ -179,6 +181,7 @@ FileHandle *mbed_override_console(int fd);
  *           possible if it's not open with current implementation).
  */
 FileHandle *mbed_file_handle(int fd);
+#endif // !MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
 }
 
 typedef mbed::DirHandle DIR;
@@ -559,6 +562,7 @@ struct pollfd {
 #if __cplusplus
 extern "C" {
 #endif
+#if !MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
     int open(const char *path, int oflag, ...);
 #ifndef __IAR_SYSTEMS_ICC__ /* IAR provides fdopen itself */
 #if __cplusplus
@@ -567,12 +571,14 @@ extern "C" {
     FILE *fdopen(int fildes, const char *mode);
 #endif
 #endif
+#endif // !MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
     ssize_t write(int fildes, const void *buf, size_t nbyte);
     ssize_t read(int fildes, void *buf, size_t nbyte);
+    int fsync(int fildes);
+#if !MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
     off_t lseek(int fildes, off_t offset, int whence);
     int ftruncate(int fildes, off_t length);
     int isatty(int fildes);
-    int fsync(int fildes);
     int fstat(int fildes, struct stat *st);
     int fcntl(int fildes, int cmd, ...);
     int poll(struct pollfd fds[], nfds_t nfds, int timeout);
@@ -586,6 +592,7 @@ extern "C" {
     long telldir(DIR *);
     void seekdir(DIR *, long);
     int mkdir(const char *name, mode_t n);
+#endif // !MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
 #if __cplusplus
 }; // extern "C"
 
@@ -619,6 +626,31 @@ std::FILE *fdopen(mbed::FileHandle *fh, const char *mode);
  */
 int bind_to_fd(mbed::FileHandle *fh);
 
+#if MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
+/** Targets may implement this to override how to write to the console.
+ *
+ * If the target hasn't provided minimal_console_putc, this is called
+ * to give the target a chance to specify a serial access to the console.
+ *
+ * If this is not provided, the console will be MinimalConsole.
+ *
+ *  @param c   The char to write
+ *  @return    The written char
+ */
+int minimal_console_putc(int c);
+
+/** Targets may implement this to override how to read from the console.
+ *
+ * If the target hasn't provided minimal_console_getc, this is called
+ * to give the target a chance to specify a serial access to the console.
+ *
+ * If this is not provided, the console will be MinimalConsole.
+ *
+ *  @return  The char read from the serial port
+ */
+int minimal_console_getc();
+#endif // MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
+
 } // namespace mbed
 
 #endif // __cplusplus