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Add semihosting and SWO examples to mbed_override_console(). #10553

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Merged
merged 2 commits into from
May 23, 2019
Merged

Add semihosting and SWO examples to mbed_override_console(). #10553

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a48d126
Add semihosting and SWO examples to mbed_override_console().
May 10, 2019
9fb4437
Update mbed_retarget.h coding style, star binds to the right.
May 23, 2019
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30 changes: 27 additions & 3 deletions platform/mbed_retarget.h
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Original file line number Diff line number Diff line change
Expand Up @@ -120,14 +120,38 @@ FileHandle *mbed_target_override_console(int fd);
* by mbed_target_override_console, else will default to serial - see
* mbed_target_override_console for more details.
*
* Example:
* Example using UARTSerial:
* @code
* FileHandle* mbed::mbed_override_console(int) {
* FileHandle *mbed::mbed_override_console(int) {
* static UARTSerial my_serial(D0, D1);
* return &my_serial;
* }
* @endcode

*
* Example using SingleWireOutput:
* @code
* FileHandle *mbed::mbed_override_console(int) {
* static SerialWireOutput swo;
* return &swo;
* }
* @endcode
*
* Example using arm semihosting:
* @code
* FileHandle *mbed::mbed_override_console(int fileno) {
* static LocalFileSystem fs("host");
* if (fileno == STDIN_FILENO) {
* static FileHandle *in_terminal;
* static int in_open_result = fs.open(&in_terminal, ":tt", O_RDONLY);
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That code is a bit RAM-inefficient, as it has two extra "once-only" control structures, and unused open results, but it's probably the simplest way of writing it.

The following would minimise RAM usage, but rather ends up obfuscating it.:

static LocalFileSystem fs("host");
struct TerminalStream {
    TerminalStream(FileSystemHandle &fs, int flags) {
        if (fs.open(&filehandle, ":tt", flags) != 0) {
            filehandle = NULL;
        }
    }
    FileHandle *filehandle;
}
if (fileno == STDIN_FILENO) {
    static TerminalStream in_terminal(fs, O_RDONLY):
    return in_terminal.filehandle;
} else {
    static TerminalStream out_terminal(fs, O_WRONLY);
    return out_terminal.filehandle;
}

You could leave it as-is; depends whether we want a simple example or to save 16 bytes of RAM when it's copy-pasted.

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Another possible refinement would be to check if the debugger is attached before attempting the open (LocalFileSystem doesn't), so it doesn't crash.

semihost_connected() should tell you that in principle, but it seems that it's currently conditional on a DEVICE_DEBUG_AWARENESS that I've never heard of and is set on basically no platforms. Not sure why - it's a core CPU feature? All M-class devices should have the bit it's trying to check.

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I think this one is so bluntly visible on the main.cpp, so maybe it would be OK to leave it as it is without the optimal memory consumption. And as you said it's a bit easier to understand.

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This semihost_connected() sounds like a nice enhancement idea. Maybe this could be checked in some future commit when the DEVICE_DEBUG_AWARENESS is more common.

* return in_terminal;
* } else {
* static FileHandle *out_terminal;
* static int out_open_result = fs.open(&out_terminal, ":tt", O_WRONLY);
* return out_terminal;
* }
* }
* @endcode
*
* @param fd file descriptor - STDIN_FILENO, STDOUT_FILENO or STDERR_FILENO
* @return pointer to FileHandle to override normal stream otherwise NULL
*/
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