Throw DOS api away, re-layout memory to fit CP/M model

boot/fat.asm

@@ -1,13 +1,15 @@
 ; Memory layout:
-%define self      0x00600 ; 1 sector
-%define fattab    0x01000 ; variable size
-%define rootdir   0x06000 ; variable size
-%define config    0x07800
-%define prog      0x07C00
+%define segment   0x00100
+
+%define self      (0x7C00-(segment<<4)) ; 1 sector
+%define fattab    (self+0x200) ; variable size
+%define rootdir   0x00100 ; variable size
+%define prog      0x0F000 ; 4K at the end for OS
 
 org self
 
 jmp short init
+dw self
 
 cluster_offset:
   dw 0
@@ -58,23 +60,16 @@ times (62 - ($-$$)) nop
 
 init:
   cli
-
-  ; Stack grows down from 64k
-  xor ax, ax
-  mov ss, ax
-  mov sp, ax
-
-  ; Relocate from [prog] to [self]
-  mov ds, ax
-  mov es, ax
-  mov si, prog
-  mov di, self
-  mov cx, 0x100
-  rep movsw
-
-  jmp 0:main
+  jmp segment:main
 
 main:
+  ; Stack grows down from 64k
+  mov ax, cs
+  mov ss, ax
+  mov sp, prog
+  mov ds, ax
+  mov es, ax
+
   mov [fdc.drv], dl ; save drive number in fd
   sti
 
@@ -110,31 +105,10 @@ main:
   mov bp, 0x3332
   jc error
 
-  ; Load config file after kernel
-  push bx
-  mov ax, config_name
-  call load_file
-  pop bx
-
-  ; Write a null byte after config file
-  mov BYTE [bx+di], 0
-
-  ; Setup registers for kernel
-  xor ax, ax
-  ; CX is size of config
-  mov cx, di
-  ; DL is drive number
-  xor dx, dx
   mov dl, [fdc.drv]
-  ; BX is offset of config
-  sub bx, prog
-  ; the pointers are 0
-  xor bp, bp
-  xor si, si
-  xor di, di
 
   ; jump into kernel
-  jmp (prog>>4):0
+  jmp segment:prog
 
 ; Load a file into memory
 ; IN	AX	pointer to 8.3 filename
@@ -260,8 +234,6 @@ error:
   int 0x16
   int 0x19
 
-config_name:
-  db "RCONFIG SYS"
 kernel_name:
   db "RDOS    SYS"