From de97bedc003f54fe185c0939d45368503e0b5169 Mon Sep 17 00:00:00 2001
From: Mateusz Faderewski <sc@mateuszfaderewski.pl>
Date: Sun, 20 Aug 2023 17:54:37 +0200
Subject: [PATCH] Improved empty save compatibility by filling initial save
 with 0xFF

---
 src/flashcart/flashcart.c |  3 +++
 src/utils/fs.c            | 36 ++++++++++++++++++++++++++++++++++++
 src/utils/fs.h            |  1 +
 3 files changed, 40 insertions(+)

diff --git a/src/flashcart/flashcart.c b/src/flashcart/flashcart.c
index 0571360c..0b241421 100644
--- a/src/flashcart/flashcart.c
+++ b/src/flashcart/flashcart.c
@@ -140,6 +140,9 @@ flashcart_error_t flashcart_load_save (char *save_path, flashcart_save_type_t sa
         if (file_allocate(save_path, SAVE_SIZE[save_type])) {
             return FLASHCART_ERROR_LOAD;
         }
+        if (file_fill(save_path, 0xFF)) {
+            return FLASHCART_ERROR_LOAD;
+        }
     }
 
     if (file_get_size(save_path) != SAVE_SIZE[save_type]) {
diff --git a/src/utils/fs.c b/src/utils/fs.c
index 549803a0..19c85814 100644
--- a/src/utils/fs.c
+++ b/src/utils/fs.c
@@ -70,6 +70,42 @@ bool file_allocate (char *path, size_t size) {
     return error;
 }
 
+bool file_fill (char *path, uint8_t value) {
+    FIL fil;
+    bool error = false;
+    uint8_t buffer[FS_SECTOR_SIZE * 8];
+    FRESULT res;
+    UINT bytes_to_write;
+    UINT bytes_written;
+
+    for (int i = 0; i < sizeof(buffer); i++) {
+        buffer[i] = value;
+    }
+
+    if (f_open(&fil, strip_sd_prefix(path), FA_WRITE) != FR_OK) {
+        return true;
+    }
+
+    for (int i = 0; i < f_size(&fil); i += sizeof(buffer)) {
+        bytes_to_write = MIN(f_size(&fil) - f_tell(&fil), sizeof(buffer));
+        res = f_write(&fil, buffer, bytes_to_write, &bytes_written);
+        if ((res != FR_OK) || (bytes_to_write != bytes_written)) {
+            error = true;
+            break;
+        }
+    }
+
+    if (f_tell(&fil) != f_size(&fil)) {
+        error = true;
+    }
+
+    if (f_close(&fil) != FR_OK) {
+        error = true;
+    }
+
+    return error;
+}
+
 bool file_get_sectors (char *path, uint32_t *sectors, size_t entries) {
     FATFS *fs;
     FIL fil;
diff --git a/src/utils/fs.h b/src/utils/fs.h
index 2f70df12..25154437 100644
--- a/src/utils/fs.h
+++ b/src/utils/fs.h
@@ -16,6 +16,7 @@ bool file_exists (char *path);
 size_t file_get_size (char *path);
 bool file_delete (char *path);
 bool file_allocate (char *path, size_t size);
+bool file_fill (char *path, uint8_t value);
 bool file_get_sectors (char *path, uint32_t *sectors, size_t entries);
 bool file_has_extensions (char *path, const char *extensions[]);