Rework interrupt handling, realign stuff for relative jumps

kernel/intr.asm

@@ -1,3 +1,34 @@
+; 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
+
 ; Register a interrupt handler
 ; in:	AL	interrupt number
 ;	ES:DI	far ptr to routine/data

kernel/main.asm

@@ -1,45 +1,18 @@
 cpu 8086
 org 0x0100
-  push cs
+jmp init
-  pop es
-  mov di, isr_dos_main
-  mov ax, 0x21
-  call intr_register
-
-  int3
-
-  cli
-.halt:
-  hlt
-  jmp .halt
 
 isr_dos_main:
-  ; Bail out if subfunction number too high
+  cmp ah, 0x01
-  cmp ah, 0x0F
+  je isr_getc_echo
-  jnc isr_invalid
+  cmp ah, 0x02
+  je isr_putc
+  jmp isr_invalid
 
-  ; allocate our return address
+%include "chario.asm"
-  push bx
+%include "intr.asm"
-  ; actual BX backup
-  push bx
 
-  ; transfer subfunction number into BX
+%include "cache.asm"
-  xor bx, bx
-  mov bl, ah
-  ; table offset = AH * 2
-  shl bx, 1
-  ; fetch from table
-  mov bx, [dos_functions+bx]
-
-  ; inject our address into the stack
-  add sp, 4
-  push bx
-  sub sp, 2
-
-  ; restore BX
-  pop bx
-  ; reads our address from the stack and jumps there
-  ret
 
 ; ISR for invalid subfunctions or unimplemented
 isr_invalid:
@@ -58,31 +31,21 @@ isr_error:
 isr_return:
   iret
 
-; Table for DOS subfunctions
+init:
-dos_functions:
+  push cs
-  ; AH 00-03
+  pop es
-  dw isr_invalid
+  mov di, isr_dos_main
-  dw isr_getc_echo
+  mov ax, 0x21
-  dw isr_putc
+  call intr_register
-  dw isr_invalid
-  ; AH 04-07
-  dw isr_invalid
-  dw isr_invalid
-  dw isr_invalid
-  dw isr_invalid
-  ; AH 08-0B
-  dw isr_invalid
-  dw isr_invalid
-  dw isr_invalid
-  dw isr_invalid
-  ; AH 0C-0F
-  dw isr_invalid
-  dw isr_invalid
-  dw isr_invalid
-  dw isr_invalid
 
-%include "intr.asm"
+  mov di, kernel_end
+  call cache_init
 
-%include "chario.asm"
+  int3
+
+  cli
+.halt:
+  hlt
+  jmp .halt
 
 kernel_end: