fs rewrite stage 2: inodes + root directory (block-based, persistent)

- fs.asm: a real block filesystem on the persistent block device - superblock,
  block/inode bitmaps, a 32-entry inode table (type, size, 8 direct block
  pointers -> files up to 2 KiB), and a root directory of 16-byte entries.
  Metadata cached in WRAMX; one-block data cache streams file/dir blocks.
- same syscall interface (open/getb/putb/list/remove) -> tools unchanged;
  ls now enumerates until flist() runs out (16 files, was hardcoded 8).
- old 8-slot WRAM FS removed; cart RAM partitioned: process banks 0-7, disk 8-11.
- two register-clobber bugs fixed: alloc_block/alloc_inode returned the
  bitmap-block number (write_bitmap clobbers C); db_use loaded the wrong block
  on a transition (db_flush->write_block clobbers C) -> multi-block files broke.
- verified: 10+ files, multi-block (300-byte) files, delete, and persistence
  across reboots. Debug 'blk' disk tool retained (fill/peek).
- README: document the block filesystem.

1 files changed, 41 insertions, 11 deletions

diff --git a/include/gbos.inc b/include/gbos.inc
index 3b96f56..770bd55 100644
--- a/include/gbos.inc
+++ b/include/gbos.inc
@@ -124,21 +124,51 @@ DEF SYS_MAX     EQU 25
 ; (SYS_OPEN=4 / SYS_CLOSE=5 are now implemented by the filesystem)
 
 ; -----------------------------------------------------------------------------
-; RAM filesystem (lives in WRAMX $D000-$DFFF, 4 KiB; fixed in DMG mode).
-; 8 files x 512 bytes: name[8] (first byte 0 = free) + len[2] + data[502].
+; Block-based filesystem (on the persistent block device; see fs.asm).
+;   block 0     superblock (magic + version)
+;   block 1     bitmaps: block bitmap @0 (16 B), inode bitmap @16 (4 B)
+;   blocks 2-3  inode table (32 inodes x 16 B)
+;   blocks 4..  data blocks
+; Metadata (bitmaps + inode table) is cached in WRAMX; data/dir blocks stream
+; through fs_datbuf / fs_dirbuf.
 ; -----------------------------------------------------------------------------
-DEF FS_BASE      EQU $D000
-DEF FS_MAX_FILES EQU 8
-DEF FS_FILE_SIZE EQU 512
-DEF FS_NAME      EQU 0
-DEF FS_LEN       EQU 8
-DEF FS_DATA      EQU 10
-DEF FS_MAX_DATA  EQU 502
+DEF BLK_SUPER   EQU 0
+DEF BLK_BITMAP  EQU 1
+DEF BLK_INODE0  EQU 2      ; inode table = blocks 2,3
+DEF BLK_DATA0   EQU 4      ; first data block
+DEF FS_VERSION  EQU 2
+DEF NINODES     EQU 32
+DEF ROOT_INO    EQU 1
+DEF NDIRECT     EQU 8      ; direct block pointers per inode -> files <= 2 KiB
+DEF DIRENTS     EQU 16     ; directory entries per block (256/16)
 
-; open-file table (kernel WRAM0): inuse, slot, mode, pos(2)
+; inode fields (16 bytes)
+DEF I_TYPE   EQU 0         ; 0=free 1=file 2=dir
+DEF I_NLINK  EQU 1
+DEF I_SIZE   EQU 2         ; 16-bit
+DEF I_BLOCKS EQU 4         ; 8 direct block pointers (1 byte each; 0=none)
+DEF IT_FREE  EQU 0
+DEF IT_FILE  EQU 1
+DEF IT_DIR   EQU 2
+
+; directory entry (16 bytes): inode(1, 0=free) + name(15, NUL-term)
+DEF DE_INO   EQU 0
+DEF DE_NAME  EQU 1
+
+; bitmap offsets within block 1
+DEF BM_BLOCKS EQU 0
+DEF BM_INODES EQU 16
+
+; WRAMX working buffers (freed by removing the old 8-slot FS)
+DEF fs_bmbuf   EQU $D000   ; 256 B: bitmap block cache (block 1)
+DEF fs_inobuf  EQU $D100   ; 512 B: inode table cache (blocks 2-3)
+DEF fs_dirbuf  EQU $D300   ; 256 B: directory block scratch
+DEF fs_datbuf  EQU $D400   ; 256 B: data block cache
+
+; open-file table (kernel WRAM0): inuse, inode, mode, pos(2)
 DEF OF_MAX   EQU 4
 DEF OF_INUSE EQU 0
-DEF OF_SLOT  EQU 1
+DEF OF_INODE EQU 1
 DEF OF_MODE  EQU 2
 DEF OF_POS   EQU 3
 DEF OF_SIZE  EQU 5