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/Stream.h

@@ -45,6 +45,7 @@ class Stream : public FileLike, private NonCopyable<Stream> {
     Stream(const char *name = NULL);
     virtual ~Stream();
 
+#if !MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
     int putc(int c);
     int puts(const char *s);
     int getc();
@@ -58,11 +59,12 @@ class Stream : public FileLike, private NonCopyable<Stream> {
     {
         return _file;
     }
+#endif // !MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
+    virtual ssize_t write(const void *buffer, size_t length);
+    virtual ssize_t read(void *buffer, size_t length);
 
 protected:
     virtual int close();
-    virtual ssize_t write(const void *buffer, size_t length);
-    virtual ssize_t read(void *buffer, size_t length);
     virtual off_t seek(off_t offset, int whence);
     virtual off_t tell();
     virtual void rewind();
@@ -72,8 +74,9 @@ class Stream : public FileLike, private NonCopyable<Stream> {
 
     virtual int _putc(int c) = 0;
     virtual int _getc() = 0;
-
+#if !MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
     std::FILE *_file;
+#endif // !MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
 
     /** Acquire exclusive access to this object.
      */

platform/cxxsupport/mstd_mutex

@@ -373,7 +373,7 @@ private:
 template <class Callable, class... Args>
 void call_once(once_flag &flag, Callable&& f, Args&&... args)
 {
-    if (!(core_util_atomic_load_explicit(&flag.__guard, mbed_memory_order_acquire) & 1)) {
+    if (!(core_util_atomic_load_explicit((uint8_t *)&flag.__guard, mbed_memory_order_acquire) & 1)) {
         if (__cxa_guard_acquire(&flag.__guard)) {
              mstd::invoke(mstd::forward<Callable>(f), mstd::forward<Args>(args)...);
              __cxa_guard_release(&flag.__guard);

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 +91,12 @@ 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 +182,7 @@ 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 +563,7 @@ 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 +572,14 @@ 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 +593,7 @@ 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 +627,31 @@ 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

platform/source/Stream.cpp

@@ -20,9 +20,14 @@
 
 namespace mbed {
 
-Stream::Stream(const char *name) : FileLike(name), _file(NULL)
+Stream::Stream(const char *name) :
+FileLike(name)
+#if !MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
+, _file(NULL)
+#endif // !MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
 {
     // No lock needed in constructor
+#if !MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
     /* open ourselves */
     _file = fdopen(this, "w+");
     // fdopen() will make us buffered because Stream::isatty()
@@ -33,14 +38,18 @@ Stream::Stream(const char *name) : FileLike(name), _file(NULL)
     } else {
         MBED_ERROR1(MBED_MAKE_ERROR(MBED_MODULE_PLATFORM, MBED_ERROR_CODE_OPEN_FAILED), "Stream obj failure", _file);
     }
+#endif // !MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
 }
 
 Stream::~Stream()
 {
+#if !MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
     // No lock can be used in destructor
     fclose(_file);
+#endif // !MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
 }
 
+#if !MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
 int Stream::putc(int c)
 {
     lock();
@@ -73,6 +82,7 @@ char *Stream::gets(char *s, int size)
     unlock();
     return ret;
 }
+#endif // !MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
 
 int Stream::close()
 {
@@ -142,6 +152,8 @@ off_t Stream::size()
     return 0;
 }
 
+#if !MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
+
 int Stream::printf(const char *format, ...)
 {
     lock();
@@ -184,4 +196,6 @@ int Stream::vscanf(const char *format, std::va_list args)
     return r;
 }
 
+#endif // !MBED_CONF_PLATFORM_STDIO_MINIMAL_CONSOLE_ONLY
+
 } // namespace mbed