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Assembly Source File | 1990-04-06 | 28.1 KB | 978 lines

;Copyright 1990 by John Wiley & Sons, Inc. ; All Rights Reserved. ; ;Generic Video Digitizer Routines in Turbo C - Computer Independent ; ; This version utilizes the 8253 timer/counter to time the sync pulses ; and should therefore be somewhat PC independent. ; ; written by Craig A. Lindley ; last update: 05/17/89 ; ;NOTE: most code in this file is written as inline code for speed reasons. ; Any change to this structure might stop the digitizer from working. ; Any change in register usage might also cause it to stop working. ; Be careful changing the parameter passing linkage with C. ; _TEXT segment byte public 'CODE' DGROUP group _DATA,_BSS assume cs:_TEXT,ds:DGROUP,ss:DGROUP _TEXT ends _DATA segment word public 'DATA' ; Field1Found DW False ;True after field 1 of video located Field1Done DW False ;True after field 1 has been digitized PrtPortData DW 0 ;data output port PrtPortIn DW 0 ;data input port (5 bits) PrtPortCont DW 0 ;cont lines output port ImageReqPtr DW 0 ;ImageReq structure pointer passed from C DigitInit DW False ;True when digitizer has been initialized CompType DW 0 ;Holds type of PC configured ; ;these variables are only used when digitizing an Interlaced image. They ;contain the address of where the next column of digitized video will be ;stored. they are necessary because Interlaced data in a single frame must ;be stored in sequential locations in the picture buffer. because two passes ;through the picture buffer are necessary it is necessary to save when the ;next column of video should be stored when we get to digitizing it. ; PColSeg DW 0 ;segment for storage for this column of video PColOff DW 0 ;Offset in PColSeg for this column storage ; _DATA ends _BSS segment word public 'BSS' _BSS ends ; ; ;General Definitions ; True EQU 0FFH ;all ones is true False EQU 0 ;all zeros is false SegOff EQU (0FFFFH/10H)+1 ;paragraphs/segment ; ;PrtPortCont bit definitions ; Strobe EQU 1 ;used to latch pixel count data SyncReset EQU 2 ;reset for sync latch Go EQU 4 ;starts pixel counter HighLow EQU 8 ;selects highlow pixel count latch ;and highlow output data PrtPortContSafe EQU 0BH ;when written to PrtPortCont ;forces all bits (4) to zero. Go bit ;is special because it has inverter ;in the hardware. ;Bit combinations ; SetGo EQU PrtPortContSafe OR Go SetStrobe EQU PrtPortContSafe AND NOT Strobe SetHighLow EQU PrtPortContSafe AND NOT HighLow SetHighLowAndGo EQU PrtPortContSafe AND NOT HighLow OR Go SetSyncReset EQU PrtPortContSafe AND NOT SyncReset SetHighLowAndStrobe EQU PrtPortContSafe AND NOT HighLow AND NOT Strobe SetSyncResetAndGo EQU PrtPortContSafe AND NOT SyncReset OR Go ResetSyncAndEOC EQU PrtPortContSafe AND NOT SyncReset AND NOT HighLow ; ;PrtPortIn bit definitions ; SyncEOC EQU 8 ;bit monitored to detect sync ;and end of conversion (EOC). ; ;Video specific definitions ; HBlankingOffset EQU 47 ;additional count required for horiz ;blanking. 3.81 usec from rising edge ;of sync pulse at 12.38 MHz. VBlankingOffset EQU 16 ;sync pulses to consume before active ;video in field. SyncsField1 EQU 272 ;Number of sync pulses in field 1 SyncsField2 EQU 271 ;ditto for field 2 ; ;ImageReq definitions ; ;This structure is sent to this code from the high level C code to tell the ;digitizer what to digitize. This declaration does not allocate space, it ;just defines the offsets of the various fields. It must correspond exactly ;with the C structure ImageReq defined in the file gvideo.h for things to ;work properly. ; ImageReq struc ; ComputerType DW 0 ;used to adjust delays according to CPU speed PrtBase DW 0 ;printer port to use with digitizer HMode DW 0 ;low or high resolution mode selector 320/640 ;pixels per line. VMode DW 0 ;non Interlace or Interlace mode. 200/480 ;lines per frame of video. NumberOfPasses DW 0 ;determines number of passes across video Flags DD 0 ;misc flags PictBufOff DW 0 ;Offset/Segment of picture buffer PictBufSeg DW 0 FirstLine DW 0 ;digitized portion of video selectors FirstPixel DW 0 LastLine DW 0 LastPixel DW 0 ; ImageReq ends ; ;The following are the equates for the various PC types. The delay MACROs ;must be adjusted to the speed of the PC. These are used to decode the ;configured type of PC and adjust the delay MACROs accordingly. These are ;all possible entries into the ComputerType field of the ImageReq. ; PC477 EQU 0 PCAT6 EQU 1 PCAT8 EQU 2 PS210 EQU 3 PS216 EQU 4 PS220 EQU 5 PS225 EQU 6 PS233 EQU 7 LowRes EQU 0 ;320 pixels/line HighRes EQU 1 ;640 pixels/line NonInterlace EQU 0 ;acquire a single field of video Interlace EQU 1 ;acquire a frame of video ; ; ;8253 Timer Definitions ;Timer 2 is used for the timing of the sync pulses. This is a more accurate ;method than a software loop. All PCs have this timer/counter available ;it is normally used to produce the beep for the keyboard. ; ;The following are timer and I/O port addresses ; Timer2CountReg EQU 42H ;used to set counter values TimerCmdReg EQU 43H ;used to send mode cmds to timer chip Timer2GateReg EQU 61H ;gate reg 8255s address TermBitReg EQU 62H ;term bit reg 8255s address ; ;The following are bit assignments, masks and mode bytes ; TimerCount EQU 18 ;at 840 nsec period =~ 15 usec Timer2GateBit EQU 01H ;gate is bit 0 of 8255 port TermCntBitMask EQU 20H ;term bit is bit 5 of 8255 port Timer2Mode EQU 0B2H ;timer 2 select; load LSB then MSB ;counter mode = 1; binary counter ; _TEXT segment byte public 'CODE' ; ;Delay MACROs ; ;Short delay. This is used to allow the computers bus to recover between ;sequential accesses of the same I/O port. ; SDelay MACRO jmp short $+2 jmp short $+2 ENDM ; ;Strobe delay. This is used to make sure the software generated strobes are ;long enough for the hardware to see. ; StbDel MACRO push ax pop ax push ax pop ax push ax pop ax push ax pop ax ENDM ; ;Start of Assembly Language Procedures ; ; ; Procedure InitializeTimer2 ; ; This procedure sets up the 8253 timer for use as a sync timer. Mode 1 of ; the counter is utilized. In this mode, when the gate signal transitions ; from a low to a high level, the counter is loaded with a previously set ; value and the counter starts counting down towards zero. When zero is ; reached, the terminal bit goes from a low to a high level. This procedure ; sets the mode for timer 2 and sets in the count for use by the Delay ; procedure. ; ; INPUT: none. ; OUTPUT: none but timer 2 is initialized and the count is loaded. ; USES: ax register. ; CALL: not callable from C. ; ; InitializeTimer2 proc near ; mov al,Timer2Mode ;load mode value out TimerCmdReg,al ;send it to the 8253 SDelay mov ax,TimerCount ;get the timers count out Timer2CountReg,al ;set the LSB of the count SDelay mov al,ah ;get the MSB of count out Timer2CountReg,al ;set the MSB of the count ret ; InitializeTImer2 endp ; ; Procedure Delay ; ; This procedure uses timer 2 to delay for approximately 15 microseconds ; time it is called. ; ; INPUT: none. ; OUTPUT: none but timer 2 is used to produce a delay ; USES: ax register ; CALL: not callable from C. ; ; Delay proc near ; push dx ;save register in al,Timer2GateReg ;read the 8255 port SDelay and al,NOT Timer2GateBit ;set bit 0 low out Timer2GateReg,al ;set gate bit low at timer 2 SDelay or al,Timer2GateBit ;set bit 0 high out Timer2GateReg,al ;set gate bit high at timer 2 SDelay Del1: in al,TermBitReg ;read the terminal bit port and al,TermCntBitMask ;is the timer period over ? jnz Del2 ;if yes jmp SDelay jmp short Del1 ; Del2: SDelay pop dx ;restore register ret ; Delay endp ; ; ; Procedure InitializeDigitizer ; ; This procedure initializes the digitizer hardware in preparation ; for usage. It is necessary to set the bits in the PrtPortCont latch ; to initialize digitizer. The HighLow line must be strobed to clear ; the SyncEOC line (because the EOC latch is then reset). If this is not ; done it is possible that the SyncEOC line will remain in a low state ; forever not allowing the Sync signal to leave the digitizer. ; ; INPUT: near pointer to the ImageReq data structure. ; OUTPUT: none but the digitizer hardware is initialized. ; USES: ax,bx,dx registers. ; CALL: callable from C. ; PROTOTYPE: InitializeDigitizer(sturct ImageReq *) ; Public _InitializeDigitizer ; _InitializeDigitizer proc near ; push bp ;prepare to retrieve the near pointer mov bp,sp ;to the ImageReq structure ; ;get and store the pointer from C which points at the ImageReq structure ; mov bx,[bp+4] ;bx pts at ImageReq mov ImageReqPtr,bx ;save in local var ; ;first thing to do is to retrieve the address of the printer port to use ;for the digitizer. we must know this for any communication with the ;digitizer. with the base address ,PrtBase, of the port known, we can easily ;calculate the other important port addresses. ; mov ax,[bx].PrtBase ;get port number to use mov PrtPortData,ax inc ax ;port+1= PrtPortIn mov PrtPortIn,ax inc ax ;port+2= PrtPortCont mov PrtPortCont,ax mov ax,[bx].ComputerType ;read the computer type mov CompType,ax ;store locally in ds ; ;now start the initialization of the digitizer hardware ; mov dx,PrtPortCont ;pt at control latch bits mov al,PrtPortContSafe ;initialize control bits out dx,al ;sent to the digitizer ; call Delay ;let things stabilize ; mov al,ResetSyncAndEOC ;set HighLow bit high out dx,al ;to clear EOC input to StbDel ; mov al,PrtPortContSafe ;initialize control bits out dx,al ;sent to the digitizer SDelay mov ax,0 ;set pixel count to 0 call SetPixelCount ;send to hardware counters SDelay call InitializeTimer2 ;initialize the sync timer mov DigitInit,True ;indicate the digitizer has been ;initialized. pop bp ;restore bp to enable a return ret ;to C code. ; _InitializeDigitizer endp ; ; ; Procedure _SyncsPerField ; ; This procedure counts the number of sync pulses (of all variety) that ; occur in a single field of video. It must do its counting in 1/30 of ; a second field time. Field 1 should contain 272 syncs while field 2 ; should contain 271. ; ; INPUT: none. ; OUTPUT: number of syncs in the monitored field returned in ax. ; USES: ax,cx,dx registers. bx perserved. ; CALL: callable from C. ; PROTOTYPE: unsigned short SyncsPerField ( void ) ; Public _SyncsPerField ; _SyncsPerField proc near ; cli ;interrupts off call SyncsPerField ;count them sti ;ints back on ret ; _SyncsPerField endp ; ; ; Procedure SyncsPerField ; ; See discussion above ; ; INPUT: none. ; OUTPUT: number of syncs in the monitored field returned in ax. ; USES: ax,cx,dx registers. bx perserved. ; CALL: not callable from C. ; ; SyncsPerField proc near ; push bx ;save register mov bx,7 ;initialize count to include all ;vertical syncs will will miss mov dx,PrtPortCont ;pt at control register mov al,ResetSyncAndEOC ;hold sync latch and EOC reset out dx,al ;so only actual sync signal will ;be seen by the hardware. SDelay ; ;read SyncEOC line to see if it is low ; dec dx ;pt back at PrtPortIn spf1: in al,dx ;read data in and al,SyncEOC jz spf1 ;jump if SyncEOC is still low. ; ;check once again. A vertical sync interval would never be high two ;reads in a row. ; call Delay in al,dx and al,SyncEOC jz spf1 ;jump if long sync. Line still low. SDelay ; ;when we get here a short sync interval has been detected. Now find ;the first long sync (vertical sync) interval with which to start the ;sync count. ; call FindLongSync ; ;1st long sync pulse found. Advance to 1st short sync interval ; spf2: in al,dx and al,SyncEOC jz spf2 ;jump if SyncEOC is still low. ; ;check again. ; call Delay in al,dx and al,SyncEOC jz spf2 ;jump if long sync. Line still low. SDelay ; ;short sync interval found again. Count up all syncs until new long sync ;is found. This indicates end of field. ; spf3: in al,dx ;read input port and al,SyncEOC ;mask all but sync bit jnz spf3 ;loop until bit active (low) SDelay ; ;Sync latch has gone low. Reset it. ; inc dx ;now pt dx at PrtPortCont for output mov al,ResetSyncAndEOC ;set SyncReset high out dx,al ;do it StbDel mov al,PrtPortContSafe ;end SyncReset pulse out dx,al ;do it ; ;read again. Short syncs should be gone ; call Delay dec dx ;pt back at PrtPortIn in al,dx and al,SyncEOC jz spf4 ;we're done when long sync detected inc bx ;count the short sync jmp spf3 ;continue looking for long ; spf4: inc dx ;pt at control port mov al,ResetSyncAndEOC ;set Sync and EOC reset high out dx,al SDelay dec dx ;pt back at input ; mov ax,bx ;result in ax for return pop bx ret ; SyncsPerField endp ; ; ; Procedure FindLongSync ; ; Assumes it is called during active video line. That is, short syncs ; are being detected. In the routine, we set the sync reset line and the ; EOC reset line (HighLow) and leave them. We are only interested in the ; detection of long (vertical) sync periods so we don't need the assistance ; of the on board sync latch IC8a. Setting these lines guarantees that only ; the actual sync pulse will be seen on the SyncEOC line. This saves us ; the time in resetting the latch inside of the loop. ; ; INPUT: none ; OUTPUT: none but returns when long sync interval detected ; USES: ax, dx registers ; CALL: not callable from C. ; PROTOTYPE: none ; FindLongSync proc near ; mov dx,PrtPortCont ;pt at control port mov al,ResetSyncAndEOC ;set both sync and EOC reset bits out dx,al SDelay dec dx ;pt at input port fls1: in al,dx ;read input port and al,SyncEOC ;mask all but sync bit jnz fls1 ;loop until bit active (low) ; ;Sync latch has gone low. By the time we realize it and read port again ;all short syncs should be gone. ; call Delay ;wait 15 usec to be sure in al,dx ;read SyncEOC line again to be sure and al,SyncEOC jnz fls1 ;loop if line is now high => short ; ;when we get here long sync interval has been detected and we're done ; SDelay ret ; FindLongSync endp ; ; ; Procedure SetPixelCount ; ; This procedure sets the pixel counter latch on the digitizer board to ; the 16 bit value in the ax register. The digitizer hardware only uses ; 12 of the 16 bits at this time. ; ; INPUT: pixel count in ax ; OUTPUT: none ; USES: ax,cx,dx registers ; CALL: not callable from C. ; ; SetPixelCount proc near ; mov cx,ax ;save pixel count in cx reg ; mov dx,PrtPortData ;pt at output data port mov al,cl ;get LS byte of count out dx,al ;write LS byte of pixel count StbDel mov dx,PrtPortCont ;pt at control port to strobe counters mov al,SetStrobe ;start the stobe pulse out dx,al StbDel mov al,PrtPortContSafe ;strobe ended out dx,al SDelay mov dx,PrtPortData ;pt at data port again mov al,ch ;get MSB of original pixel count out dx,al ;send to pixel counter StbDel mov dx,PrtPortCont ;pt at control port to set HighLow high mov al,SetHighLow out dx,al StbDel mov al,SetHighLowAndStrobe ;strobe into counters out dx,al StbDel mov al,SetHighLow ;reset Strobe leave HighLow still high out dx,al StbDel mov al,SetSyncReset ;reset sync latch out dx,al StbDel mov al,PrtPortContSafe ;HighLow now low out dx,al SDelay ret ; SetPixelCount endp ; ; ; Procedure _SetPixelCount ; ; C callable version of above. ; ; INPUT: pixel count ; OUTPUT: none ; USES: ax,cx,dx registers ; CALL: callable from C. ; PROTOTYPE: void SetPixelCount ( unsigned short ) ; ; Public _SetPixelCount ; _SetPixelCount proc near ; push bp mov bp,sp mov ax,[bp+4] call SetPixelCount pop bp ret ; _SetPixelCount endp ; ; ; Procedure _GetPicture ; ; This procedure digitizes a complete monochrome picture. It stores ; the data for the picture in a buffer whos address is passed to it from C. ; The function InitializeDigitizer must be called before this one so that ; the hardware and software are setup correctly. All instructions for how ; the digitizer should digitize a picture are contained in the ImageReq ; data structure. ; ; INPUT: BX is a near pointer to the ImageReq structure which contains all ; the information for the control of the digitizer. ; OUTPUT: returns True is picture data in buffer, False if error ; USES: all registers. saves bp,si and di registers as required by Turbo C ; CALL: callable from C. ; PROTOTYPE: GetPicture(); ; PUBLIC _GetPicture ; _GetPicture proc near ; cmp DigitInit,True ;has digitizer been initialized ? je gp1 ;continue if so mov ax,False ;return a false indication to C ret gp1: push bp ;save for use by C push si ;save si,di in case register vars push di ;used in C code. ; mov bx,ImageReqPtr ;get ImageReq pointer into bx for use ;all struct references use bx as ptr mov es,[bx].PictBufSeg ;point es:bp at picture data buffer mov bp,[bx].PictBufOff mov PColSeg,es ;establish addr of 1st video column mov PColOff,bp mov Field1Done,False ;indicate field 1 not yet digitized mov Field1Found,False ;and has not been found yet mov si,[bx].FirstPixel ;get the first pixels (column) # cmp [bx].HMode,LowRes ;320 pixel line ? jne gp2 ;jump if not shl si,1 ;if 320 pixel line pixel # * 2 gp2: add si,HBlankingOffset ;add in the blanking interval ; ;this is the top of the loop which digitizes a complete column of pixels ;from the video signal. CPU register si is the pixel count across a line ;whereas register di is the line count down the video image. ; gp3: mov Field1Done,False ;false until field 1 has been done mov di,[bx].FirstLine ;initialize line count to that ;specified in the ImageReq every ;time thru this loop mov es,PColSeg ;get address of this column mov bp,PColOff ; mov ax,si ;get pixel count call SetPixelCount ;load hardware pixel counters ; gp4: cmp Field1Found,True ;have we located desired field before? je gp7 ;if yes just find long sync interval ; ;when we get here we need to find the start of the first field at least once ; gp5: cli ;interrupts off from now on call SyncsPerField ;locate field 1 cmp ax,SyncsField2 ;are we there ? jmp gp6 ;if start of field 1 then jump sti ;interrupts back on call Delay ;delay for short period call Delay ;delay for short period call Delay ;delay for short period jmp short gp5 ;repeat until we find it ; ;start of first field found ; gp6: mov Field1Found,True ;indicate it was found jmp short gp8 ; ;when we get here we just need to find the start of every subsequent ;even or odd field ; gp7: cli ;interrupts off from here on mov di,[bx].FirstLine ;initialize line count call FindLongSync ;find vertical sync period ; ;when we get here we have located the start of a field. NOTE: both the ;Sync and the EOC reset lines are still held active because we are not ;afraid of missing a short sync. That is, we are still only interested in ;long sync intervals. In the code that follows, we will ;continuously read the input port until we see it go high indicating a ;short sync has been detected. At that point we are past all of the long ;sync pulses and can start counting out the vertical blanking interval. ; gp8: in al,dx and al,SyncEOC jz gp8 ;jump if SyncEOC is still low. ; ;check once more ; call Delay ;delay 15 usec to be sure its gone in al,dx and al,SyncEOC jz gp8 ;jump if long sync. Line still low. SDelay ; ;we've just found the 1st short sync interval. Its probably an equalization ;pulse. We must now consume all of the equalization and vertical blanking ;pulses to get to the start of the active video. ; inc dx ;pt at control port mov al,PrtPortContSafe ;end SyncReset pulse out dx,al ;so we can use latch to find all ;syncs no matter how small SDelay dec dx ;pt back at input port ; ;count off the number of lines in the field to ignor. If a full field/frame ;picture is being digitized then ignor only VBlankingOffset number. If a ;partial picture is being digitized, ignor VBlankingOffset + FirstLine number ;of lines. ; mov cx,VBlankingOffset ;consume this many on default picture ; ;check for field 2 digitization ; cmp Field1Done,True ;are we digitizing field 2 ? jne gp9 ;jmp if not inc cx ;if we are consume one more sync ;pulse to get rid of 1/2 line gp9: cmp [bx].FirstLine,0 ;req pict starts at line 0 ? je gp10 ;jmp if so add cx,[bx].FirstLine ;else add in additional lines to ignor gp10: in al,dx ;read input port and al,SyncEOC ;mask all but sync bit jnz gp10 ;loop until sync seen SDelay ; ;Sync latch has gone low. Reset it. ; inc dx ;now pt dx at PrtPortCont for output mov al,ResetSyncAndEOC ;set SyncReset high out dx,al ;do it StbDel mov al,PrtPortContSafe ;end SyncReset pulse out dx,al ;do it SDelay ; ;Sync latch is now reset. SyncEOC line should go inactive (high) shortly ;because we are expecting only short sync pulses. ; dec dx ;pt at PrtPortIn dec cx ;one less sync to consume jnz gp10 ;still more ? ; ;we have now consumed all the vertical blanking sync pulses. Set Go so ;pixel counters will be triggered on rising edge of sync pulse from camera. ; inc dx ;pt at control port mov al,SetGo ;set the go bit so counters will be out dx,al ;triggered by rising edge of sync SDelay dec dx ;pt at input port ; ;we are now at the start of the active video line. We must now process each ;digitization in less than one line time of 63.5 usec. ; gp11: in al,dx ;look for falling edge of sync pulse and al,SyncEOC jnz gp11 SDelay ; ;line started with falling edge of SyncEOC ; inc dx ;pt at Cont port mov al,SetSyncResetAndGo ;reset sync latch and keep Go ;line high to start pixel count out dx,al ;on rising edge of every sync StbDel mov al,SetGo ;end SyncReset but leave Go active out dx,al ;do it SDelay ; ;Sync latch is now reset and pixel counters should be running. ;SyncEOC line should go active (low) shortly when the converted data becomes ;available. ; dec dx ;pt at PrtPortIn gp12: in al,dx ;read input port mov cl,al ;copy data to cl reg and al,SyncEOC ;mask all but EOC bit jnz gp12 ;loop until data ready SDelay ; ;we now have four bits of the video digital data in cl register as follows: ; 7 6 5 4 3 2 1 0 ; D D D D EOC X X X ;after we shift it right four places it looks like ; 7 6 5 4 3 2 1 0 ; 0 0 0 0 D D D D ; shr cl,1 shr cl,1 shr cl,1 shr cl,1 ; ;prepare to retrieve the MS nibble of data from the digitizer ; inc dx ;pt at Cont port mov al,SetHighLowAndGo ;set High/Low high to get 2 MSBs. out dx,al ;this also resets EOC SDelay dec dx in al,dx ;get the two MSBs and al,30H ;mask all but bits of interest or cl,al ;combine to get 6 total bits/pixel ; mov es:[bp],cl ;store all 6 bits of data ; gp13: inc dx ;pt at Cont port mov al,SetGo ;HighLow low again leave Go active out dx,al ;do it dec dx ; ;check to see if pointer for data storage (bp register) will leave a 64K ;segment. If so the segment register must be adjusted by SEGOFF so ;offset 0 into the segment points at the next available byte of storage. ;NOTE: when digitizing an interlaced picture, where it is necessary to ;skip every other location in the picture buffer, the check for segment end ;must be slightly different. To accomodate this, the code that follows is ;executed conditionally depending upon interlaced digitization or not. ; cmp [bx].VMode,Interlace ;are we in interlace mode ? je gp15 ;jmp if so ; ;when we get here we are in non Interlace mode ; cmp bp,0FFFFH ;at end of seg ? jne gp14 ;jump if not mov ax,es ;get seg reg value add ax,SEGOFF ;add offset mov es,ax ;store it back ;segment offset will inc to 0000 ; ;check to see if we are done with a column of pixels ; gp14: inc bp ;bump the data pointer inc di ;inc the line count cmp di,[bx].LastLine ;bottom of picture ? jb gp11 ; mov PColSeg,es ;save ptr to next storage location mov PColOff,bp ; jmp gp19 ;jmp to common exit code ; ;when we get here we are in Interlace mode ; gp15: cmp bp,0FFFEH ;at end of seg ? jb gp16 ;jump if not mov ax,es ;get seg reg value add ax,SEGOFF ;add offset mov es,ax ;store it back ;seg offset will inc to 0000 ; gp16: inc bp ;bump the data pointer inc bp ;and again to leave room for data from ;other field inc di ;inc the line count mov ax,[bx].LastLine ;get last line of Interlaced frame shr ax,1 ;divide by two for last line per field cmp di,ax ;bottom of field ? jae gp17 jmp gp11 ; ;we are now done with one field of video for the Interlaced image. Go ;back and digitize the other field. ; gp17: cmp Field1Done,True ;done with this column in both fields ? je gp18 ;jmp if so ; ;when we get here we know we need to go back and do the other field ; mov Field1Done,True ;set flag to say we're finished on ;next pass mov es,PColSeg ;reload this columns pointer mov bp,PColOff ; inc bp ;bump one to miss data from other ;field jmp gp7 ;get next fields data ; gp18: mov PColSeg,es ;save addr of where next columns dec bp mov PColOff,bp ;data should start ; ;we are now done with a column of the video display. Advance to next pixel ;or next column. This is true for both Interlace and non Interlace ;digitizations. ; gp19: inc dx ;pt at Cont port mov al,PrtPortContSafe ;reset all control lines out dx,al ;just to be safe SDelay sti ;interrupts back on because timing ;between frames is not that critical cmp [bx].HMode,LowRes ;a 320 pixel picture ? jne gp20 ;jmp if not ; ;when we get here we know we are digitizing a 320 pixel line picture. we ;must increment the pixel count twice (two 640 pixels = one 320 pixel) ;and check to see if we are done digitizing a picture. this is complicated ;by the fact that the pixel counts are actually twice as big so we must ;compare with twice the LastPixel value. ; inc si inc si mov ax,[bx].LastPixel ;get the final pixel count shl ax,1 ;* 2 for comparison add ax,HBlankingOffset ;added in blanking interval cmp si,ax ;is the 320 pixel pict done ? jae gp21 ;jmp if so jmp gp3 ;if not do next pixel column ; ;when we get here we know we are digitizing a 640 pixel line picture. This ;is a much easier case than the 320 pixel picture shown above. ; gp20: inc si ;bump pixel count once for high res mov ax,[bx].LastPixel ;get last pixel # add ax,HBlankingOffset ;added in blanking interval cmp si,ax ;is the 640 pixel pict done ? jae gp21 ;if so jump jmp gp3 ;if not do next pixel column ; ;a complete picture is now digitized. Prepare to return to C. ; gp21: pop di pop si pop bp mov ax,True ;indicate no error to C ret ; _GetPicture endp ; ;End of video routines ; _TEXT ends end