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, 12 insertions, 53 deletions

diff --git a/src/blk.asm b/src/blk.asm
index ea04e95..2be961e 100644
--- a/src/blk.asm
+++ b/src/blk.asm
@@ -83,57 +83,6 @@ write_block::
     restore_bank
     ret
 
-; -----------------------------------------------------------------------------
-; blk_format - write a fresh superblock (magic) to block 0. (mkfs, stage 1)
-; -----------------------------------------------------------------------------
-blk_format::
-    ld hl, wCopyBuf             ; zero the buffer
-    ld b, 0
-    xor a
-.z
-    ld [hl+], a
-    dec b
-    jr nz, .z
-    ld hl, wCopyBuf
-    ld a, SUPER_MAG0
-    ld [hl+], a
-    ld a, SUPER_MAG1
-    ld [hl+], a
-    ld a, SUPER_MAG2
-    ld [hl+], a
-    ld a, SUPER_MAG3
-    ld [hl], a
-    ld a, SUPER_BLOCK
-    ld hl, wCopyBuf
-    call write_block
-    ret
-
-; -----------------------------------------------------------------------------
-; blk_init - format the disk only if it isn't already formatted (magic check).
-; Called at boot; the disk otherwise persists across power cycles (.sav).
-; -----------------------------------------------------------------------------
-blk_init::
-    ld a, SUPER_BLOCK
-    ld hl, wCopyBuf
-    call read_block
-    ld hl, wCopyBuf
-    ld a, [hl+]
-    cp SUPER_MAG0
-    jr nz, .fmt
-    ld a, [hl+]
-    cp SUPER_MAG1
-    jr nz, .fmt
-    ld a, [hl+]
-    cp SUPER_MAG2
-    jr nz, .fmt
-    ld a, [hl]
-    cp SUPER_MAG3
-    jr nz, .fmt
-    ret                         ; already formatted
-.fmt
-    call blk_format
-    ret
-
 ; =============================================================================
 ; [debug] block poke/peek syscalls, to validate the layer + persistence.
 ; =============================================================================
@@ -152,10 +101,20 @@ sys_bfill::
     xor a
     ret
 
-; sys_bpeek(B = block) -> A = block's first byte
+; sys_bpeek(B = block, E = offset) -> A = block[offset]
 sys_bpeek::
+    ld a, e
+    ld [wFsByte], a             ; stash offset
     ld a, b
     ld hl, wCopyBuf
     call read_block
-    ld a, [wCopyBuf]
+    ld hl, wCopyBuf
+    ld a, [wFsByte]
+    add l
+    ld l, a
+    ld a, h
+    adc 0
+    ld h, a
+    ld a, [hl]
     ret
+