kernel.asm

GNU FreeDOS兼容MS DOS很好的东东.

; kernel startup stack
                global  init_tos
                resw 512
init_tos:
; the last paragraph of conventional memory might become an MCB
                resb 16
		global __init_end
__init_end:
init_end:        

segment	_DATA
; blockdev private stack
                global  blk_stk_top
                times 192 dw 0
blk_stk_top:

; clockdev private stack
                global  clk_stk_top
                times 64 dw 0
clk_stk_top:

; Dynamic data:
; member of the DOS DATA GROUP
; and marks definitive end of all used data in kernel data segment
;

segment _DATAEND

_swap_indos:
; we don't know precisely what needs to be swapped before this, so set it here.
; this is just after FIXED_DATA+BSS+DATA and before (D)CONST+BSS
; probably, the clock and block stacks and disktransferbuffer should go past
; _swap_indos but only if int2a ah=80/81 (critical section start/end)
; are called upon entry and exit of the device drivers

                times 96 dw 0x9090 ; Process 0 Stack
                global  _p_0_tos
_p_0_tos:

segment DYN_DATA

        global _Dyn
_Dyn:
        DynAllocated dw 0
        
segment ID_B
    global __INIT_DATA_START
__INIT_DATA_START:
segment ID_E
    global __INIT_DATA_END
__INIT_DATA_END:


segment	INIT_TEXT_START
                global  __InitTextStart
__InitTextStart:                    ; and c version


;
; start end end of HMA area

segment	HMA_TEXT_START
                global __HMATextAvailable
__HMATextAvailable
                global  __HMATextStart
__HMATextStart:   
 
; 
; the HMA area is filled with 1eh+3(=sizeof VDISK) = 33 byte dummy data,
; so nothing will ever be below 0xffff:0031
;
segment HMA_TEXT
begin_hma:              
                times 10h db 0   ; filler [ffff:0..ffff:10]
                times 20h db 0
                db 0

; to minimize relocations
		global _DGROUP_
_DGROUP_	dw DGROUP

%ifdef WATCOM
;               32 bit multiplication + division
global __U4M
__U4M:
		LMULU
global __U4D
__U4D:
                LDIVMODU
%endif

		resb 0xd0 - ($-begin_hma)
		; reserve space for far jump to cp/m routine
		resb 5

;End of HMA segment                
segment	HMA_TEXT_END
                global  __HMATextEnd
__HMATextEnd:                   ; and c version



; The default stack (_TEXT:0) will overwrite the data area, so I create a dummy
; stack here to ease debugging. -- ror4

segment	_STACK	class=STACK stack



    

segment	CONST
        ; dummy interrupt return handlers

		global _int22_handler
                global _int28_handler
                global _int2a_handler
                global _empty_handler
_int22_handler:		
_int28_handler:
_int2a_handler:
_empty_handler:
                iret
    

global _initforceEnableA20
initforceEnableA20:
		call near forceEnableA20
		retf   

    global __HMARelocationTableStart
__HMARelocationTableStart:   

                global  _int2f_handler
                extern  reloc_call_int2f_handler
_int2f_handler: jmp 0:reloc_call_int2f_handler
                call near forceEnableA20

                global  _int20_handler
                extern  reloc_call_int20_handler
_int20_handler: jmp 0:reloc_call_int20_handler
                call near forceEnableA20

                global  _int21_handler
                extern  reloc_call_int21_handler
_int21_handler: jmp 0:reloc_call_int21_handler
                call near forceEnableA20


                global  _low_int25_handler
                extern  reloc_call_low_int25_handler
_low_int25_handler: jmp 0:reloc_call_low_int25_handler
                call near forceEnableA20

                global  _low_int26_handler
                extern  reloc_call_low_int26_handler
_low_int26_handler: jmp 0:reloc_call_low_int26_handler
                call near forceEnableA20

                global  _int27_handler
                extern  reloc_call_int27_handler
_int27_handler: jmp 0:reloc_call_int27_handler
                call near forceEnableA20

                global  _int0_handler
                extern  reloc_call_int0_handler
_int0_handler:  jmp 0:reloc_call_int0_handler
                call near forceEnableA20

                global  _int6_handler
                extern  reloc_call_int6_handler
_int6_handler:  jmp 0:reloc_call_int6_handler
                call near forceEnableA20

                global  _cpm_entry
                extern  reloc_call_cpm_entry
_cpm_entry:     jmp 0:reloc_call_cpm_entry
                call near forceEnableA20

                global  _reloc_call_blk_driver
                extern  _blk_driver
_reloc_call_blk_driver:
                jmp 0:_blk_driver
                call near forceEnableA20

                global  _reloc_call_clk_driver
                extern  _clk_driver
_reloc_call_clk_driver:
                jmp 0:_clk_driver
                call near forceEnableA20

                global  _CharMapSrvc ; in _DATA (see AARD)
                extern  _reloc_call_CharMapSrvc
_CharMapSrvc:   jmp 0:_reloc_call_CharMapSrvc
                call near forceEnableA20

                global _init_call_p_0
                extern reloc_call_p_0
_init_call_p_0: jmp  0:reloc_call_p_0
                call near forceEnableA20


   global __HMARelocationTableEnd
__HMARelocationTableEnd:    

;
; if we were lucky, we found all entries from the outside to the kernel.
; if not, BUMS
;
;
; this routine makes the HMA area available. PERIOD.
; must conserve ALL registers
; will be only ever called, if HMA (DOS=HIGH) is enabled.
; for obvious reasons it should be located at the relocation table
;
    global _XMSDriverAddress
_XMSDriverAddress:  
                    dw 0            ; XMS driver, if detected
                    dw 0

    global _ENABLEA20
_ENABLEA20:
    mov ah,5
UsingXMSdriver:    
    push bx
    call far [cs:_XMSDriverAddress]
    pop  bx
    retf

    global _DISABLEA20
_DISABLEA20:
    mov ah,6
    jmp short UsingXMSdriver

dslowmem  dw 0
eshighmem dw 0ffffh

    global forceEnableA20
forceEnableA20:

    push ds
    push es
    push ax
    
forceEnableA20retry:    
    mov  ds, [cs:dslowmem]
    mov  es, [cs:eshighmem]
    
    mov ax, [ds:00000h]    
    cmp ax, [es:00010h]    
    jne forceEnableA20success

    mov ax, [ds:00002h]    
    cmp ax, [es:00012h]    
    jne forceEnableA20success

    mov ax, [ds:00004h]    
    cmp ax, [es:00014h]    
    jne forceEnableA20success

    mov ax, [ds:00006h]    
    cmp ax, [es:00016h]    
    jne forceEnableA20success

;
;   ok, we have to enable A20 )at least seems so
;

    call far _ENABLEA20
    
    jmp short forceEnableA20retry
    
    
    
forceEnableA20success:    
    pop ax
    pop es
    pop ds
    ret
		
;
; global f*cking compatibility issues:
;
; very old brain dead software (PKLITE, copyright 1990)
; forces us to execute with A20 disabled
;

global _ExecUserDisableA20

_ExecUserDisableA20:

    cmp word [cs:_XMSDriverAddress],0
    jne NeedToDisable
    cmp word [cs:_XMSDriverAddress+2],0
    je noNeedToDisable
NeedToDisable:        
    push ax 
    call far _DISABLEA20
    pop ax
noNeedToDisable:
    iret        


;
; Default Int 24h handler -- always returns fail
; so we have not to relocate it (now)
;
FAIL            equ     03h

                global  _int24_handler
_int24_handler: mov     al,FAIL
                iret

;
; this makes some things easier
;

segment _LOWTEXT
                global _TEXT_DGROUP
_TEXT_DGROUP dw DGROUP

segment INIT_TEXT
                global _INIT_DGROUP
_INIT_DGROUP dw DGROUP