Assembly Source series of Frespace

This is the past DOS era of the compilation of source code, although has passed, but for the study of the assembly is still helpful, assembly language is just a basic programmer language, most people can grasp, not necessarily in-depth research.

; Frespace. ASM 10/04/84 GWF
;
;
;
; Call Frespace (AH,AL,BH,BL,CH,CL). CL SHOULD is 0 for default
; Drive 1 for A, 2 for B, 3 for C, etc. The value of the
; The other variables does is not matter. They'll come back
; With a meaningful value.
;
; An EXAMPLE program:
;
; Ten DefInt A-Z
; Color 7,1:cls
; test1=1:ah=0:al=0:bh=0:ch=0:cl=1:test2=2
; INPUT "DRIVE 0=default, 1=a, 2=b, 3=c"; Cl
; Notoginseng PRINT "JUST before call"
; Call Frespace (AH,AL,BH,BL,CH,CL)
; PRINT "JUST after call"
; PRINT "ah="; AH; " Al= "; Al; " Bh= "; BH; " Bl= "; BL; " Ch= "; CH; " Cl= "; CL;
; Ufree!=256*ah+al
; Ubytes!=256*bh+bl
; Usector!=256*ch+cl
; PRINT "ufree!=";　ufree!; " Ubytes!= ";　 ubytes!; " Usector!= "; usector!
; MB frespace!=ufree!*ubytes!*usector!
; frespace!= PRINT ""; frespace!
; PRINT "This SHOULD to be 1", TEST1
; 130 PRINT "This SHOULD to be 2", TEST2
;
Get_spa equ 36h; Get disk free spaces function call
Doscall equ 21h;D os interrupt number
Dgroup Group Datarea
Datarea segment para public ' DATA '
Ah_ret DW? ; Ah to is sent back
Al_ret DW? ; Al to being sent back
Bh_ret DW? ; BH to is sent back
Bl_ret DW? ; BL to is sent back
Ch_ret DW? ; Ch to is sent back
Cl_ret DW? ; Cl to is sent back
Datarea ENDS
;
CSEG segment ' CODE '
Assume Cs:cseg
Public Frespace
frespace proc Far
Push BP; BP from BASIC
MOV bp,sp set base for Parm list
Push DS;D s from basic work area
Push es; es from basic work area
MOV ax,datarea; establish data addressability
MOV Ds,ax now DS are local data
Assume Ds:datarea
;
;
;
;
Push BP
Sub Ax,ax
mov si,ss:[bp+6]; get addr of parameter
mov al,es:[si]; get value of Parm
MOV dx,ax;d l contains the drive number on call
;d h'll be zero
mov Ah,get_spa; Get Space function number
int doscall; Call DOS
; Move the values into local work area to prepare to send back to basic
Xchg Dx,ax must have a word. Want to zero out DH.
Sub Ax,ax; Produce the Zero
Xchg Dx,ax; DX is now zero.
; DH is what we really want as zero.
MOV dl,ah; Want to send back a byte
MOV ah_ret,dx; Prepare to return AH
MOV dl,al; Want to send back a byte
MOV al_ret,dx; Prepare to return AL
MOV dl,bh; Want to send back a byte
MOV bh_ret,dx; Prepare to return BH
MOV dl,bl; Want to send back a byte
MOV bl_ret,dx; Prepare to return BL
MOV dl,ch; Want to send back a byte
MOV ch_ret,dx; Prepare to return CH
MOV dl,cl; Want to send back a byte
MOV cl_ret,dx; Prepare to return CL
; Go back
Pop bp; get back Basic ' s workspace
MOV Ax,cl_ret
MOV si,ss:[bp+6]
mov Es:[si],ax; return cl
MOV Ax,ch_ret
MOV Si,ss:[bp+8]
mov es:[si],ax; return ch
MOV Ax,bl_ret
MOV si,ss:[bp+10]
mov es:[si],ax; return bl
MOV Ax,bh_ret
MOV si,ss:[bp+12]
mov es:[si],ax; return BH
MOV Ax,al_ret
MOV si,ss:[bp+14]
mov Es:[si],ax; return al
MOV Ax,ah_ret
MOV si,ss:[bp+16]
MOV es:[si],ax; return AH
;
Pop es
Pop ds
Pop bp
RET to basic 6 parameters were sent
Frespace ENDP
;-----------------------------------------------------------------------
Cseg ends
End to Assembler