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 segment   0x00100
-%define fattab    0x01000 ; variable size
+
-%define rootdir   0x06000 ; variable size
+%define self      (0x7C00-(segment<<4)) ; 1 sector
-%define config    0x07800
+%define fattab    (self+0x200) ; variable size
-%define prog      0x07C00
+%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
-
+  jmp segment:main
-  ; 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
 
 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"
 

kernel/chario.asm

@@ -1,35 +0,0 @@
-; Reads a single character with echo
-; out	AL	character
-isr_getc_echo:
-  xor ax, ax
-  int 0x16
-  test al, al
-  jz isr_getc_echo
-  call putc
-  iret
-
-; Reads a single character without echo
-; out   AL      character
-isr_getc:
-  xor ax, ax
-  int 0x16
-  test al, al
-  jz isr_getc
-  iret
-
-; Prints a single character
-; in	DL	character
-isr_putc:
-  push ax
-  mov al, dl
-  call putc
-  pop ax
-  iret
-
-putc:
-  push bx
-  mov ah, 0x0e
-  mov bx, 0x0000
-  int 0x10
-  pop bx
-  ret

kernel/drive.asm

@@ -1,53 +0,0 @@
-; drive table
-%define drivetab_type    0x00 ; BYTE  0=unassigned, 1=BIOS/CHS, 2=BIOS/LBA
-%define drivetab_num     0x01 ; BYTE  DL number
-
-; CHS data for type=1
-; Might be reused for driver address
-%define drivetab_heads   0x02 ; WORD  CHS heads
-%define drivetab_spt     0x04 ; WORD  CHS sectors per track
-
-%define drivetab_sectors 0x06 ; DWORD total number of sectors
-%define drivetab_offset  0x0A ; DWORD partition offset
-%define drivetab_size    0x0E
-
-drive_table:
-  dw 0
-.count:
-  dw 4
-
-; DI is incremented for the space taken
-; IN	ES:DI
-drive_setup:
-  xor cx, cx
-  mov [drive_table], di
-  mov al, drivetab_size
-  mov ah, BYTE [drive_table.count]
-  mul ah
-  xchg cx, ax
-  ; this increments DI and also fills table with zeros
-  rep stosb
-  ret
-
-; Load a drive table entry
-; IN    DL      drive number
-; OUT   DS:SI   ptr to table item
-drive_load:
-  ; bail out if number too high
-  cmp dl, [cs:drive_table.count]
-  jnc .err
-
-  push cs
-  pop ds
-  mov si, [drive_table]
-
-  push ax
-  mov al, drivetab_size
-  mul dl
-  add si, ax
-  pop ax
-
-  ret
-.err:
-  stc
-  ret

kernel/intr.asm

@@ -1,30 +0,0 @@
-; Register a interrupt handler (21h AH=25h)
-; in:	AL	interrupt number
-;	DS:DX	far ptr
-isr_intr_register:
-  ; backup previous stos ptr
-  push es
-  push di
-
-  ; DI = AL * 4
-  mov ah, 4
-  mul ah
-  mov di, ax
-
-  ; ES = 0
-  xor ax, ax
-  mov es, ax
-
-  ; store offset
-  mov ax, dx
-  stosw
-
-  ; store segment
-  mov ax, ds
-  stosw
-
-  ; restore previous stos ptr
-  pop di
-  pop es
-
-  iret

kernel/main.asm

@@ -1,64 +1,57 @@
 cpu 8086
-org 0x0
+
+; Memory layout (starting from top)
+%define self	0xF000
+%define diskbuf (self-0x200)
+%define stack   (diskbuf) ; end addr, grows down
+
+org self
 jmp init
 
-isr_dos_main:
+banner:
-  cmp ah, 0x01
+  db "RDOS 2019-09", 0x0A, 0x0D, 0
-  je isr_getc_echo
-  cmp ah, 0x02
-  je isr_putc
-  cmp ah, 0x25
-  je isr_intr_register
-  jmp isr_invalid
 
-%include "intr.asm"
+print_banner:
-%include "chario.asm"
+  mov cl, 2
-
+  mov si, banner
-; ISR for invalid subfunctions or unimplemented
+.loop:
-isr_invalid:
+  mov dl, BYTE [si]
-  mov bp, 0xFEFE
+  test dl, dl
-  int3
+  jz .end
-.hlt:
+  call cpm_syscall
-  hlt
+  inc si
-  jmp .hlt
+  jmp .loop
-; ISR tail to set carry flag to signal error
+.end:
-isr_error:
+  ret
-  push bp
-  mov bp, sp
-  ; set carry flag
-  or WORD [SS:BP+6], 1
-  pop bp
-isr_return:
-  iret
-
-%include "drive.asm"
 
 init:
-  mov ax, cs
+  mov sp, stack
-  mov ds, ax
-  mov es, ax
 
-  call config_first_run
+  call print_banner
-
+  int3
-  mov di, kernel_end
-  call drive_setup
-
-  mov dx, isr_dos_main
-  mov ax, 0x2521
-  pushf
-  push cs
-  call isr_dos_main
-
-  mov dl, 0x37
-  mov ah, 0x02
-  int 0x21
 
   cli
 .halt:
   hlt
   jmp .halt
 
+cpm_syscall:
+  cmp cl, 0x02
+  je putc
+  stc
+  ret
+
+putc:
+  push ax
+  push bx
+  mov al, dl
+  mov ah, 0x0e
+  mov bx, 0x0000
+  int 0x10
+  pop bx
+  pop ax
+  ret
+
 %include "string.asm"
-%include "config.asm"
 
 kernel_end: