codal_port/microbitfs: Add a hook for when files are opened for writing.

And reset the log if main.py is opened for writing.

Addresses issue #95.

Signed-off-by: Damien George <damien@micropython.org>

src/codal_port/main.c

@@ -42,6 +42,8 @@
 #include "drv_display.h"
 #include "modmicrobit.h"
 
+#define MAIN_PY "main.py"
+
 // Use a fixed static buffer for the heap.
 static char heap[64 * 1024];
 
@@ -65,7 +67,7 @@ void mp_main(void) {
         mp_init();
 
         if (pyexec_mode_kind == PYEXEC_MODE_FRIENDLY_REPL) {
-            const char *main_py = "main.py";
+            const char *main_py = MAIN_PY;
             if (mp_import_stat(main_py) == MP_IMPORT_STAT_FILE) {
                 // exec("main.py")
                 microbit_pyexec_file(main_py);
@@ -183,6 +185,14 @@ void microbit_pyexec_file(const char *filename) {
     }
 }
 
+// Callback from microbitfs when a file is opened for writing.
+void microbit_file_opened_for_writing(const char *name, size_t name_len) {
+    if (name_len == strlen(MAIN_PY) && memcmp(name, MAIN_PY, name_len) == 0) {
+        // The file main.py is changed, so invalidate the data logging storage (fast erase).
+        microbit_hal_log_delete(false);
+    }
+}
+
 #if MICROPY_MBFS
 mp_lexer_t *mp_lexer_new_from_file(const char *filename) {
     return uos_mbfs_new_reader(filename);

src/codal_port/microbitfs.c

@@ -25,6 +25,9 @@
  * THE SOFTWARE.
  */
 
+// This is a copy of the file micropython:ports/nrf/modules/uos/microbitfs.c with
+// a call to `microbit_file_opened_for_writing` added in `microbit_file_open`.
+
 #include <string.h>
 #include <stdio.h>
 #include <sys/stat.h>
@@ -351,6 +354,7 @@ STATIC file_descriptor_obj *microbit_file_open(const char *name, size_t name_len
         flash_write_byte((uint32_t)&(file_system_chunks[index].marker), FILE_START);
         flash_write_byte((uint32_t)&(file_system_chunks[index].header.name_len), name_len);
         flash_write_bytes((uint32_t)&(file_system_chunks[index].header.filename[0]), (uint8_t*)name, name_len);
+        microbit_file_opened_for_writing(name, name_len);
     } else {
         if (index == FILE_NOT_FOUND) {
             return NULL;

src/codal_port/mpconfigport.h

@@ -191,4 +191,7 @@ typedef long mp_off_t;
 // Needed for MICROPY_PY_URANDOM_SEED_INIT_FUNC.
 extern uint32_t rng_generate_random_word(void);
 
+// Needed for microbitfs.c:microbit_file_open.
+void microbit_file_opened_for_writing(const char *name, size_t name_len);
+
 #endif