Block device peripheral and SBFS file system implemented.

Source/DiskTool/sbfs.h

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+// sbfs.h
+// The SplitBit Filesystem, version one.
+//
+// This is the host side's copy of the format. The other implementation is SplitBit
+// assembly running on the machine itself, so nothing can be shared between them except
+// the specification: the two have to be kept honest by a document rather than by a
+// header. Everything here follows that document exactly, and anything that changes here
+// has to change there in the same breath.
+//
+// All multi byte numbers are most significant byte first, the same as every other number
+// SplitBit stores: addresses, the SPBT binary header, and the vector table.
+//
+// Written by Anachronaut
+
+#ifndef SBFS_H
+#define SBFS_H
+
+#include <stdint.h>
+
+#define SBFS_MAGIC "SBFS"
+#define SBFS_MAGIC_BYTES 4
+#define SBFS_VERSION 1
+
+#define SBFS_BLOCK_BYTES 256
+
+// ---- Block 0, the superblock ----
+//
+//   0   4  "SBFS"
+//   4   1  Version
+//   5   1  Reserved
+//   6   2  Blocks on the disk
+//   8   2  First directory block
+//   10  2  Blocks the directory occupies
+//   12  2  Free blocks, a cache rather than the authority
+//   14     Reserved to the end of the block
+
+#define SBFS_SUPER_VERSION    4
+#define SBFS_SUPER_DISK       6
+#define SBFS_SUPER_DIRSTART   8
+#define SBFS_SUPER_DIRBLOCKS  10
+#define SBFS_SUPER_FREE       12
+
+// ---- Directory entries ----
+//
+//   0   1  Flags
+//   1   2  First block of the file's data
+//   3   2  Whole blocks the file occupies
+//   5   1  Bytes in the trailing part block, or zero if there is not one
+//   6  22  Name, padded with zeroes
+//   28  4  Reserved
+//
+// Thirty two divides two hundred and fifty six, so an entry never straddles a block and
+// reading one never means handling a split.
+
+#define SBFS_ENTRY_BYTES 32
+#define SBFS_ENTRIES_PER_BLOCK (SBFS_BLOCK_BYTES / SBFS_ENTRY_BYTES)
+
+#define SBFS_ENTRY_FLAGS  0
+#define SBFS_ENTRY_START  1
+#define SBFS_ENTRY_BLOCKS 3
+#define SBFS_ENTRY_TAIL   5
+#define SBFS_ENTRY_NAME   6
+#define SBFS_NAME_BYTES   22
+
+#define SBFS_FLAG_IN_USE 0x01
+
+// The directory begins at block 1 and is this many blocks unless told otherwise, which
+// is sixty four files. The superblock carries the real number, so this is only what a
+// freshly formatted disk gets.
+#define SBFS_FIRST_DIRECTORY_BLOCK 1
+#define SBFS_DEFAULT_DIRECTORY_BLOCKS 8
+
+// A file of n bytes occupies n / 256 whole blocks and, if anything is left over, one more
+// for the tail. Zero means zero in both, so an empty file occupies nothing at all.
+#define SBFS_WHOLE_BLOCKS(bytes) ((bytes) / SBFS_BLOCK_BYTES)
+#define SBFS_TAIL_BYTES(bytes)   ((bytes) % SBFS_BLOCK_BYTES)
+#define SBFS_BLOCKS_USED(blocks, tail) ((blocks) + ((tail) ? 1 : 0))
+
+#endif // SBFS_H