From a65f54b121418fc270f3444997148a6c48d616bf Mon Sep 17 00:00:00 2001
From: Ain <41307858+nero@users.noreply.github.com>
Date: Sat, 12 Oct 2019 18:33:26 +0000
Subject: [PATCH] Advance on FCB disk i/o

---
 kernel/drive.asm | 14 +++++++++
 kernel/exec.asm  | 10 +++++--
 kernel/fcb.asm   | 77 +++++++++++++++++++++++++++++++++---------------
 kernel/main.asm  | 22 +++++++-------
 4 files changed, 84 insertions(+), 39 deletions(-)

diff --git a/kernel/drive.asm b/kernel/drive.asm
index cdb1600..04599ac 100644
--- a/kernel/drive.asm
+++ b/kernel/drive.asm
@@ -67,3 +67,17 @@ drive_read:
   jnz .try
   stc
   jmp .giveup
+
+; Seek to fcb_off given in a ptr
+; IN	BX	ptr to FCB
+drive_seek:
+  push ax
+  push cx
+  mov cl, [bx+fcb_ss]
+  add cl, 7
+  mov ax, 1
+  sal ax, cl
+  int3
+  pop cx
+  pop ax
+  ret
diff --git a/kernel/exec.asm b/kernel/exec.asm
index 2632196..6c8f963 100644
--- a/kernel/exec.asm
+++ b/kernel/exec.asm
@@ -3,12 +3,16 @@ exec_chain:
   mov si, 0x81
 exec:
   push bx
-  sub sp, fcb_size
+  sub sp, 0x20
   mov bx, sp
 
   call fcb_parse
-  call fcb_open_rootdir
+  call fcb_open_blockdev
+  mov cx, 5
+.loop:
+  call fcb_getc
+  loop .loop
 
-  add sp, fcb_size
+  add sp, 0x20
   pop bx
   ret
diff --git a/kernel/fcb.asm b/kernel/fcb.asm
index b17064d..a5a174c 100644
--- a/kernel/fcb.asm
+++ b/kernel/fcb.asm
@@ -1,49 +1,50 @@
 ; User-accessible part of FCB (12 bytes)
-%define fcb_drv   0 ; 1 byte
+%define fcb_drv   0 ; 1 byte, 1=A: 2=B: 3=C:
 %define fcb_fn    1 ; 8 bytes
 %define fcb_ext   9 ; 3 bytes
 
-; Drive & FS data (4 bytes)
+; Drive & FS data (6 bytes)
 %define fcb_spt   12 ; byte    sectors per track
 %define fcb_nos   13 ; byte    number of sides/heads
-%define fcb_ss    14 ; byte    sector size: 2^ss
-%define fcb_cs    15 ; byte    cluster size: 2^(ss+cs)
+%define fcb_ss    14 ; byte    sector size: 0=128, 1=256, 2=512, ...
+%define fcb_cs    15 ; byte    cluster size: 0=128, 1=256, 2=512, ...
+%define fcb_co    16 ; word    start sector for theoretical cluster 0
 
-; Read/Write pointer (12 bytes):
-; Will be overwritten by new filename for CL=17
-%define fcb_fsize 16 ; dword   file size
-%define fcb_fptr  20 ; dword   handle position
-%define fcb_clus  24 ; word    current cluster fptr points in
-%define fcb_co    26 ; word    start sector for theoretical cluster 0
+; Read/Write pointer (6 bytes)
+%define fcb_left  18 ; word    number of bytes left to read from diskbuf
+%define fcb_off   20 ; dword   offset in disk (not in file)
 
-; Link to directory item (3 bytes)
-%define fcb_ds    28 ; word    directory sector
-%define fcb_do    30 ; byte    directory offset
+; Link to directory item (4 bytes)
+%define fcb_ds    24 ; dword   offset of directory item
 
-fcb_open_rootdir:
-  cmp byte [bx], 0
-  jne .drivedone
-  mov al, default_drive
-  mov [bx], al
-.drivedone:
-  mov dl, [bx]
+%define fcb_end   32
+
+fcb_open_blockdev:
+  mov dl, 0x01
+  mov [bx], dl
   dec dl
 
+  ; Init non-user FCB data with zero
   xor ax, ax
   xor dx, dx
-  ; set directory sector to 0 (=rootdir)
-  mov [bx+fcb_ds], ax
+  lea di, [bx+fcb_spt]
+  mov cx, (fcb_end - fcb_spt)
+  rep stosb
+
   ; load first sector
   call drive_read
 
-  ; transfer sector size
+  ; copy sector size
   mov ax, [diskbuf + 0x0B]
   call log2
+  sub ax, 7
   mov byte [bx+fcb_ss], al
 
-  ; transfer cluster size
+  ; copy cluster size
+  xor ah, ah
   mov al, [diskbuf + 0x0D]
   call log2
+  add al, [bx+fcb_ss]
   mov byte [bx+fcb_cs], al
 
   ; transfer sectors per track
@@ -54,4 +55,32 @@ fcb_open_rootdir:
   mov al, [diskbuf + 0x1A]
   mov byte [bx+fcb_nos], al
 
+  ; first 128 bytes are always valid
+  mov WORD [bx+fcb_left], 0x80
+
+  ret
+
+fcb_get_sector_mask:
+  push cx
+  xor ax, ax
+  not ax
+  mov cl, [bx+fcb_ss]
+  add cl, 7
+  shl ax, cl
+  pop cx
+  ret
+
+fcb_getc:
+  push bx
+  call drive_seek
+  call fcb_get_sector_mask
+  not ax
+  and ax, [bx+fcb_off]
+  xchg ax, bx
+  add bx, diskbuf
+  mov al, [bx]
+  pop bx
+  add word [bx+fcb_off], 1
+  adc word [bx+fcb_off+2], 0
+  dec word [bx+fcb_left]
   ret
diff --git a/kernel/main.asm b/kernel/main.asm
index 83a0e6c..76be6db 100644
--- a/kernel/main.asm
+++ b/kernel/main.asm
@@ -3,17 +3,17 @@ cpu 8086
 ; Memory layout (starting from top)
 %define self    0xF000
 
-; A single sector for disk i/o
+; A single sector for deblocking
 %define diskbuf (self-0x200)
 
-; DWORD partition offset for C: and D:
-%define parttab (diskbuf - (2*4))
+%define stack   (diskbuf)
 
-%define stack   (parttab)
+; Metadata for current disk sector
+%define diskptr 0x50
+%define disknum 0x54
+%define diskflg 0x55
 
-%define default_drive BYTE [0x5B]
-
-%define fcb_size 31
+%define default_drive BYTE [0x4]
 
 org self
 jmp init
@@ -28,11 +28,8 @@ init:
   mov dx, banner
   call print_string
 
-  mov dx, 0x79
-  mov byte [0x79], 0x7F
-  call read_buffer
-  mov ax, [0x79]
-  int3
+  mov si, init_program
+  call exec
 
   cli
 .halt:
@@ -63,3 +60,4 @@ cpm_syscall:
 %include "fcbparse.asm"
 %include "drive.asm"
 %include "log2.asm"
+%include "dump.asm"