我想在我的代码中提到 DEVRD = 0000 0100(即十进制 4 或中断 04h，用于溢出)和 DRDWRHL = 0001 0110(即十进制 22 或中断 16h，用于键盘输入)。 在这里我很困惑，为什么我们要把这里 (0000 0100 SHL 8) 放在 CH 中，(0001 0110)放在 CL 中。 我们试图放置两种中断类型(04H 表示溢出)是什么意思和 16h 用于键盘输入)进入计数器寄存器 CX。什么是计数器寄存器 CX 在这里做什么。
我更具体地提到：这里 DEVRD 代表设备读取，DRDWTHL 代表设备读写标头大小。 提前谢谢。
;
; Device call routines for MSDOS
;
INCLUDE DOSSEG.ASM
IFNDEF KANJI
KANJI EQU 0 ;FALSE
ENDIF
CODE SEGMENT BYTE PUBLIC 'CODE'
ASSUME SS:DOSGROUP,CS:DOSGROUP
.xlist
.xcref
INCLUDE DOSSYM.ASM
INCLUDE DEVSYM.ASM
.cref
.list
TITLE DEV - Device call routines
NAME Dev
i_need IOXAD,DWORD
i_need IOSCNT,WORD
i_need DEVIOBUF,4
i_need IOCALL,BYTE
i_need IOMED,BYTE
i_need IORCHR,BYTE
i_need CALLSCNT,WORD
i_need DMAAdd,DWORD
i_need NullDevPt,DWORD
i_need CallDevAd,DWORD
i_need Attrib,BYTE
i_need NULDEV,DWORD
i_need Name1,BYTE
i_need DevPt,DWORD
i_need DPBHead,DWORD
i_need NumIO,BYTE
i_need ThisDPB,DWORD
i_need DevCall,DWORD
i_need VerFlg,BYTE
SUBTTL IOFUNC -- DO FUNCTION 1-12 I/O
PAGE
IOFUNC_RETRY:
ASSUME DS:NOTHING,ES:NOTHING
invoke restore_world
procedure IOFUNC,NEAR
ASSUME DS:NOTHING,ES:NOTHING
; Inputs:
; DS:SI Points to FCB
; AH is function code
; = 0 Input
; = 1 Input Status
; = 2 Output
; = 3 Output Status
; = 4 Flush
; AL = character if output
; Function:
; Perform indicated I/O to device or file
; Outputs:
; AL is character if input
; If a status call
; zero set if not ready
; zero reset if ready (character in AL for input.
status)
; For regular files:
; Input Status
; Gets character but restores fcb_RR field
; Zero set on EOF
; Input
; Gets character advances fcb_RR field
; Returns ^Z on EOF
; Output Status
; Always ready
; AX altered, all other registers preserved
MOV WORD PTR [IOXAD+2],SS
MOV WORD PTR [IOXAD],OFFSET.
DOSGROUP:DEVIOBUF
MOV WORD PTR [IOSCNT],1
MOV WORD PTR [DEVIOBUF],AX
IOFUNC2:
TEST [SI.fcb_DEVID],080H
JNZ IOTODEV
JMP IOTOFILE
IOTODEV:
invoke save_world
PUSH DS
PUSH SS
POP ES
PUSH SS
POP DS
ASSUME DS:DOSGROUP
XOR BX,BX
MOV [IOCALL.REQSTAT],BX
MOV BYTE PTR [IOMED],BL
MOV BX,OFFSET DOSGROUP:IOCALL
MOV CX,(DEVRD SHL 8) OR DRDWRHL // I am in trouble here.
OR AH,AH
JZ DCALLR
MOV CX,(DEVRDND SHL 8) OR DRDNDHL
DEC AH
JZ DCALLR
MOV CX,(DEVWRT SHL 8) OR DRDWRHL
DEC AH
JZ DCALLO
MOV CX,(DEVOST SHL 8) OR DSTATHL
DEC AH
JZ DCALLO
DFLUSH:
MOV CX,(DEVIFL SHL 8) OR DFLSHL
DCALLR:
MOV AH,86H
DCALL:
MOV [IOCALL.REQLEN],CL
MOV [IOCALL.REQFUNC],CH
MOV CL,AH
POP DS
ASSUME DS:NOTHING
CALL DEVIOCALL
MOV DI,[IOCALL.REQSTAT]
TEST DI,STERR
JZ OKDEVIO
MOV AH,CL
invoke CHARHARD
CMP AL,1
JZ IOFUNC_RETRY
;Know user must have wanted ignore. Make sure device.
shows ready so
;that DOS doesn't get caught in a status loop when user.
simply wants
;to ignore the error.
AND BYTE PTR [IOCALL.REQSTAT+1], NOT (STBUI.
SHR 8)
OKDEVIO:
PUSH SS
POP DS
ASSUME DS:DOSGROUP
CMP CH,DEVRDND
JNZ DNODRD
MOV AL,BYTE PTR [IORCHR]
MOV [DEVIOBUF],AL
DNODRD: MOV AH,BYTE PTR [IOCALL.REQSTAT+1]
NOT AH ; Zero = busy, not zero = ready
AND AH,STBUI SHR 8
invoke restore_world
ASSUME DS:NOTHING
MOV AX,WORD PTR [DEVIOBUF]
return
DCALLO:
MOV AH,87H
JMP SHORT DCALL
IOTOFILE:
ASSUME DS:NOTHING
OR AH,AH
JZ IOIN
DEC AH
JZ IOIST
DEC AH
JZ IOUT
return ; NON ZERO FLAG FOR OUTPUT.
STATUS
IOIST:
PUSH WORD PTR [SI.fcb_RR] ; Save position
PUSH WORD PTR [SI.fcb_RR+2]
CALL IOIN
POP WORD PTR [SI.fcb_RR+2] ; Restore position
POP WORD PTR [SI.fcb_RR]
return
IOUT:
CALL SETXADDR
invoke STORE
invoke FINNOSAV
CALL RESTXADDR ; If you change this into a jmp.
don't come
return ; crying to me when things don't work
ARR
IOIN:
CALL SETXADDR
invoke LOAD
PUSH CX
invoke FINNOSAV
POP CX
OR CX,CX ; Check EOF
CALL RESTXADDR
MOV AL,[DEVIOBUF] ; Get byte from trans addr
retnz
MOV AL,1AH ; ^Z if EOF
return
SETXADDR:
POP WORD PTR [CALLSCNT] ; Return address
invoke save_world
PUSH WORD PTR [DMAADD] ; Save Disk trans.
addr
PUSH WORD PTR [DMAADD+2]
PUSH DS
PUSH SS
POP DS
ASSUME DS:DOSGROUP
MOV CX,WORD PTR [IOXAD+2]
MOV WORD PTR [DMAADD+2],CX
MOV CX,WORD PTR [IOXAD]
MOV WORD PTR [DMAADD],CX ; Set byte trans.
addr
MOV CX,[IOSCNT] ; ioscnt specifies length of
buffer
POP DS
ASSUME DS:NOTHING
MOV [SI.fcb_RECSIZ],1 ; One byte per record
MOV DX,SI ; FCB to DS:DX
invoke GETRRPOS
JMP SHORT RESTRET ; RETURN ADDRESS
RESTXADDR:
POP WORD PTR [CALLSCNT] ; Return address
POP WORD PTR [DMAADD+2] ; Restore Disk trans
addr
POP WORD PTR [DMAADD]
invoke restore_world
RESTRET:JMP WORD PTR [CALLSCNT] ; Return
address
IOFUNC ENDP
SUBTTL DEVIOCALL, DEVIOCALL2 - CALL A DEVICE
PAGE
procedure DEVIOCALL,NEAR
ASSUME DS:NOTHING,ES:NOTHING
; Inputs:
; DS:SI Points to device FCB
; ES:BX Points to request data
; Function:
; Call the device
; Outputs:
; None
; DS:SI,AX destroyed, others preserved
LDS SI,DWORD PTR [SI.fcb_FIRCLUS]
entry DEVIOCALL2
; As above only DS:SI points to device header on entry,
and DS:SI is preserved
MOV AX,[SI.SDEVSTRAT]
MOV WORD PTR [CALLDEVAD],AX
MOV WORD PTR [CALLDEVAD+2],DS
CALL DWORD PTR [CALLDEVAD]
MOV AX,[SI.SDEVINT]
MOV WORD PTR [CALLDEVAD],AX
CALL DWORD PTR [CALLDEVAD]
return
DEVIOCALL ENDP
SUBTTL DEVNAME - LOOK FOR NAME OF DEVICE
PAGE
procedure DEVNAME,NEAR
ASSUME DS:DOSGROUP,ES:DOSGROUP
; Inputs:
; DS,ES:DOSGROUP
; Filename in NAME1
; Function:
; Determine if file is in list of I/O drivers
; Outputs:
; Carry set if name not found
; ELSE
; Zero flag set
; BH = Bit 7,6 = 1, bit 5 = 0 (cooked mode)
; bits 0-4 set from low byte of attribute word
; DEVPT = DWORD pointer to Device header of device
; Registers BX destroyed
PUSH SI
PUSH DI
PUSH CX
IF KANJI
PUSH WORD PTR [NAME1]
CMP [NAME1],5
JNZ NOKTR
MOV [NAME1],0E5H
NOKTR:
ENDIF
TEST BYTE PTR [ATTRIB],attr_volume_id ; If looking
for VOL id don't find devs
JNZ RET31
MOV SI,OFFSET DOSGROUP:NULDEV
LOOKIO:
ASSUME DS:NOTHING
TEST [SI.SDEVATT],DEVTYP
JZ SKIPDEV ; Skip block devices
PUSH SI
ADD SI,SDEVNAME
MOV DI,OFFSET DOSGROUP:NAME1
MOV CX,4 ; All devices are 8 letters
REPE CMPSW ; Check for name in list
POP SI
JZ IOCHK ; Found it?
SKIPDEV:
LDS SI,DWORD PTR [SI] ; Get address of next
device
CMP SI,-1 ; At end of list?
JNZ LOOKIO
RET31: STC ; Not found
RETNV: PUSH SS
POP DS
ASSUME DS:DOSGROUP
IF KANJI
POP WORD PTR [NAME1]
ENDIF
POP CX
POP DI
POP SI
RET
IOCHK:
ASSUME DS:NOTHING
MOV WORD PTR [DEVPT+2],DS ; Save pointer to
device
MOV BH,BYTE PTR [SI.SDEVATT]
OR BH,0C0H
AND BH,NOT 020H ;Clears Carry
MOV WORD PTR [DEVPT],SI
JMP RETNV
DevName ENDP
procedure GetBP,NEAR
ASSUME DS:DOSGROUP,ES:NOTHING
; Inputs:
; AL = Logical unit number (A = 0)
; Function:
; Find Drive Parameter Block
; Outputs:
; ES:BP points to DPB
; [THISDPB] = ES:BP
; Carry set if unit number bad
; No other registers altered
LES BP,[DPBHEAD] ; Just in case drive isn't valid
AND AL,3FH ; Mask out dirty and device bits
CMP AL,BYTE PTR [NUMIO]
CMC
JC GOTDPB ; Get drive A
FNDDPB:
CMP AL,ES:[BP.dpb_drive]
JZ GOTDPB ; Carry is clear if jump executed
LES BP,ES:[BP.dpb_next_dpb]
JMP SHORT FNDDPB
GOTDPB:
MOV WORD PTR [THISDPB],BP
MOV WORD PTR [THISDPB+2],ES
RET
GetBP ENDP
SUBTTL SETREAD, SETWRITE -- SET UP HEADER BLOCK
PAGE
procedure SETREAD,NEAR
ASSUME DS:NOTHING,ES:NOTHING
; Inputs:
; DS:BX = Transfer Address
; CX = Record Count
; DX = Starting Record
; AH = Media Byte
; AL = Unit Code
; Function:
; Set up the device call header at DEVCALL
; Output:
; ES:BX Points to DEVCALL
; No other registers effected
PUSH DI
PUSH CX
PUSH AX
MOV CL,DEVRD
SETCALLHEAD:
MOV AL,DRDWRHL
PUSH SS
POP ES
MOV DI,OFFSET DOSGROUP:DEVCALL
STOSB ; length
POP AX
STOSB ; Unit
PUSH AX
MOV AL,CL
STOSB ; Command code
XOR AX,AX
STOSW ; Status
ADD DI,8 ; Skip link fields
POP AX
XCHG AH,AL
STOSB ; Media byte
XCHG AL,AH
PUSH AX
MOV AX,BX
STOSW
MOV AX,DS
STOSW ; Transfer addr
POP CX ; Real AX
POP AX ; Real CX
STOSW ; Count
XCHG AX,DX ; AX=Real DX, DX=real CX, CX=real AX
STOSW ; Start
XCHG AX,CX
XCHG DX,CX
POP DI
MOV BX,OFFSET DOSGROUP:DEVCALL
RET
entry SETWRITE
ASSUME DS:NOTHING,ES:NOTHING
; Inputs:
; DS:BX = Transfer Address
; CX = Record Count
; DX = Starting Record
; AH = Media Byte
; AL = Unit Code
; Function:
; Set up the device call header at DEVCALL
; Output:
; ES:BX Points to DEVCALL
; No other registers effected
PUSH DI
PUSH CX
PUSH AX
MOV CL,DEVWRT
ADD CL,[VERFLG]
JMP SHORT SETCALLHEAD
SETREAD ENDP
do_ext
CODE ENDS
END
但我想在我的代码中提到 DEVRD = 0000 0100(即十进制 4 或用于溢出的中断 04h)
和 DRDWRHL = 0001 0110(即十进制 22 或中断 16h，用于键盘输入)。 在这里我很困惑，为什么我们要把这里 (0000 0100 SHL 8) 放在 CH 中，(0001 0110) 放在 CL 中。 我们试图放置两种中断类型是什么意思(04h for溢出和键盘输入 16h)进入计数器寄存器 CX。什么是计数器寄存器 CX 在这里做什么。
此处使用字大小CX寄存器方便地编写较短的代码。
指令
MOV CX,(DEVRD SHL 8) OR DRDWRHL
相当于
MOV CL, DRDWRHL
MOV CH, DEVRD
CX版本需要 3 个字节，CLCH版本需要 4 个字节。
由于该技术重复多次，因此可以节省大量资金。
我们试图将两种中断类型(04H 用于溢出，16h 用于键盘输入)放入计数器寄存器 CX 中是什么意思
事实并非如此。如果你进一步查看程序，你会发现CL存储在变量IOCALL中。雷克伦。一个明确暗示长度的名称。CL以临时方式使用的进一步证据来自这样一个事实，即在它被AH中的任何值(86h 或 87h)覆盖后不久。