Add incomplete filesystem prototype

3 files changed, 139 insertions, 1 deletions

diff --git a/src/filesystem.c b/src/filesystem.c
new file mode 100644
index 0000000..2da77be
--- /dev/null
+++ b/src/filesystem.c
@@ -0,0 +1,118 @@
+// We need 64 * 32 bytes (2K) of SRAM for file indexes. To avoid corruption
+// issues we ignore the first file (32 bytes).
+// Note that the filename should include the null terminator if we want to use
+// strcmp.
+#define FILE_NAME_SIZE     27
+#define FILE_CAPACITY      63
+#define FILE_HEADER_OFFSET 2
+#define FILE_INDEX_OFFSET  32
+#define FILE_DATA_OFFSET   KB(2)
+#define FILE_MAX_SIZE      KB(1)
+#define SRAM               ((vu8*)(MEM_CART))
+
+typedef struct File {
+    char name[FILE_NAME_SIZE + 1];
+    u16 size;
+    u16 mem_offset; // NOTE: Unused...
+} File;
+
+// The filesystem header.
+typedef struct FileSystem {
+    u16 num_files;
+    u16 data_size; // NOTE: Unused...
+    u16 data_capacity; // NOTE: Unused...
+    File files[FILE_CAPACITY];
+} FileSystem;
+
+static FileSystem filesystem;
+
+void
+_fs_read(u8 *dst, size_t pos, size_t n_bytes) {
+    for (size_t i = 0; i < n_bytes; ++i) {
+        dst[i] = SRAM[pos + i];
+    }
+}
+
+void
+_fs_write(u8 *src, size_t pos, size_t n_bytes) {
+    for (size_t i = 0; i < n_bytes; ++i) {
+        SRAM[pos + i] = src[i];
+    }
+}
+
+void
+fs_init() {
+    // Load header if existing.
+    _fs_read(&filesystem, FILE_HEADER_OFFSET, offsetof(FileSystem, files));
+    if (filesystem.num_files == 0xFFFF
+            && filesystem.data_capacity == 0xFFFF
+            && filesystem.data_size == 0xFFFF) {
+        filesystem.num_files = 0;
+        filesystem.data_size = 0;
+        filesystem.data_capacity = 27 * FILE_MAX_SIZE;
+        memset(&filesystem.files, 0, FILE_CAPACITY * sizeof(File));
+        _fs_write(&filesystem, FILE_HEADER_OFFSET, offsetof(FileSystem, files));
+    } else {
+        _fs_read(&filesystem.files, FILE_INDEX_OFFSET, sizeof(File) * filesystem.num_files);
+    }
+}
+
+int
+fs_open_file(char *name) {
+    // Try to find an existing file.
+    for (size_t i = 0; i < filesystem.num_files; ++i) {
+        // TODO: Replace strcmp with vectorized fixed size char comparison.
+        if (strcmp(name, filesystem.files[i].name) == 0) {
+            return i;
+        }
+    }
+    // Create a new file if there is space.
+    if (filesystem.num_files < FILE_CAPACITY) {
+        size_t index = filesystem.num_files++;
+        size_t k = 0;
+        while(*name) {
+            filesystem.files[index].name[k++] = *name++;
+        }
+        filesystem.files[index].size = 0;
+        filesystem.files[index].mem_offset = 0;
+
+        // Update file index.
+        _fs_write(&filesystem.files[index],
+                FILE_INDEX_OFFSET + index * sizeof(File),
+                sizeof(File));
+
+        // Update header.
+        _fs_write(&filesystem, FILE_HEADER_OFFSET, offsetof(FileSystem, files));
+
+        return index;
+    }
+    return -1;
+}
+
+int
+fs_write(u8 *src, size_t n_bytes, u16 file_index, u16 offset, bool append) {
+    File *file = &filesystem.files[file_index];
+
+    // Check if there is enough capacity for this write operation.
+    if (offset + n_bytes >= FILE_MAX_SIZE) {
+        return -1;
+    }
+
+    // Write data to file block.
+    _fs_write(src, FILE_DATA_OFFSET + FILE_MAX_SIZE * file_index + offset, n_bytes);
+
+    // Update file index.
+    if (append) {
+        if (offset + n_bytes > file->size) {
+            file->size = offset + n_bytes;
+        }
+    } else {
+        file->size = offset + n_bytes;
+    }
+    _fs_write(file, FILE_INDEX_OFFSET + file_index * sizeof(File), sizeof(File));
+
+    // Update header.
+    _fs_write(&filesystem, FILE_HEADER_OFFSET, offsetof(FileSystem, files));
+
+    return n_bytes;
+}
diff --git a/src/main.c b/src/main.c
index 6f5034b..798dc18 100644
--- a/src/main.c
+++ b/src/main.c
@@ -3,6 +3,7 @@
 #include "common.h"
 #include "bitmap.h"
 #include "bd-font.c"
+#include "filesystem.c"
 
 #include "uxn/uxn.h"
 #include "uxn/uxn.c"
@@ -266,6 +267,25 @@ int main(void) {
             }, &ppu.fg);
     txt_position(0,0);
 
+    fs_init();
+
+    // DEBUG:...
+    int file_idx;
+    if ((file_idx = fs_open_file("HELLO_FILE")) >= 0) {
+        fs_write("HEY", 3, file_idx, 0, false);
+        fs_write("THERE", 3, file_idx, 1, true);
+        txt_printf("nam: %s\n", filesystem.files[file_idx].name);
+        txt_printf("num: %d\n", filesystem.num_files);
+        txt_printf("size: %d\n", filesystem.files[file_idx].size);
+    }
+    if ((file_idx = fs_open_file("HELLO_FOLKS")) >= 0) {
+        fs_write("BY GOD", 6, file_idx, 0, false);
+        fs_write("XXX", 3, file_idx, 1, true);
+        txt_printf("nam: %s\n", filesystem.files[file_idx].name);
+        txt_printf("num: %d\n", filesystem.num_files);
+        txt_printf("size: %d\n", filesystem.files[file_idx].size);
+    }
+
     // Main loop.
     int frame_counter = 0;
     evaluxn(&u, 0x0100);
diff --git a/src/text.h b/src/text.h
index 1142a73..06e3973 100644
--- a/src/text.h
+++ b/src/text.h
@@ -132,7 +132,7 @@ txt_putc_hybrid(char c) {
         int x = text_engine.cursor_x;
         int y = text_engine.cursor_y;
         Tile *buf = text_engine.memory;
-        buf[x + y * 30] = tile;
+        buf[x + y * 32] = tile;
         dirty_tiles[y] |= 1 << x;
         text_engine.cursor_x += 1;
         if (text_engine.cursor_x >= 30) {