TRIPOS PDP-11 Assembler version 1.4 ; @(#)follow.11 1.1 (mg@ukc) 4/9/88 ; Follow light pen around with a blob ; Constants about machine. 020000 COREND = 8.*1024. ; First unusable word 002000 WIDTH = 1024. ; Height of display 001400 HEIGHT = 768. ; Width of display ; Address of registers. 172000 DPC = 172000 ; VT40 Program counter 172002 DSR = 172002 ; VT40 Status register 172004 XSR = 172004 ; X status register 172006 YSR = 172006 ; Y status register ; Addresses of interrupt vectors 000320 STOPVEC = 320 000324 LPVEC = 324 ; Recommended mnemomics for Display processor instructions 100000 CHAR = 100000 ; Character mode 104000 SHORTV = 104000 ; Short vector mode 110000 LONGV = 110000 ; Long vector mode 114000 POINT = 114000 ; Point mode 120000 GRAPHX = 120000 ; Graphplot X mode 124000 GRAPHY = 124000 ; Graphplot Y mode 130000 RELATV = 130000 ; Relative point mode 002000 INT0 = 2000 ; Intensity modes 002200 INT1 = 2200 002400 INT2 = 2400 002600 INT3 = 2600 003000 INT4 = 3000 003200 INT5 = 3200 003400 INT6 = 3400 003600 INT7 = 3600 000100 LPOFF = 100 ; Light pen off 000140 LPON = 140 ; and on 000020 BLKOFF = 20 ; Blink off 000030 BLKON = 30 ; and on 000004 LINE0 = 4 ; Solid line 000005 LINE1 = 5 ; Long dash 000006 LINE2 = 6 ; Short dash 000007 LINE3 = 7 ; Dot dash 160000 DJMP = 160000 ; Display jump 164000 DNOP = 164000 ; Display NOP 170000 STATSA = 170000 ; Load status A 173400 DSTOP = 173400 ; Display stop and interrupt 001400 SINON = 1400 ; Stop interrupt on 001000 SINOFF = 1000 ; Stop interrupt off 000200 LPLITE = 200 ; Light pen hit on 000300 LPDARK = 300 ; and off 000040 ITAL0 = 40 ; Italics off 000060 ITAL1 = 60 ; and on 000004 SYNC = 4 ; Halt and resume in Sync 174000 STATSB = 174000 ; Load status B 000100 INCR = 100 ; Graphplot increment 040000 INTX = 40000 ; Intensify vector or point 001777 MAXX = 1777 ; Max delta-x 001377 MAXY = 1377 ; Max delta-y 020000 MINUSX = 20000 ; -ve delta-x 020000 MINUSY = 20000 ; -ve delta-y 017600 MAXSX = 17600 ; Max delta-x in short mode 000077 MAXSY = 77 ; Max delta-y 020000 MISVX = 20000 ; -ve delta-x 000100 MISVY = 100 ; -ve delta-y 000000' .PSECT ; Simple PDP-11 program 000000' 012706 017776 MOV #COREND-2,SP ; Set up stack ; set up interrupt vectors 000004' 012737 000100' 000324 MOV #LPINTR,@#LPVEC ; light pen hit 000012' 012737 000200 000326 MOV #200,@#LPVEC+2 ; new priority = BR4 (exclude further DPU interrupts) 000020' 012737 000142' 000320 MOV #STOPINTR,@#STOPVEC ; display proram stop 000026' 012737 000200 000322 MOV #200,@#STOPVEC+2 ; new priority = BR4 000034' 005067 000032 CLR XACC 000040' 005067 000030 CLR YACC 000044' 005067 000026 CLR NHIT ; start it off 000050' 012705 000300' MOV #DLOOP,R5 ; restart address 000054' 012704 172000 MOV #DPC,R4 ; cache addr of DPC 000060' 012737 000276' 172000 MOV #DPROG,@#DPC 000066' 000001 IDLE: WAIT ; and hang around 000070' 000776 BR IDLE ; Strategy: draw eight lines from around the current centre to the ; current centre point. If the pen is pointing at the centre, this ; will cause 8 light pen hits per display.Add them up, divide by N, ; and this gives you the centre of the light pen hit area. ; total of x- and y-coords of light pen hits (up to eight hits) 000072' 000001 XACC: .WORD 1 000074' 000001 YACC: .WORD 1 000076' 000001 NHIT: .WORD 1 ; number of LP hits thie display 000100' LPINTR: ; Find position of hit 000100' 013700 172004 MOV @#XSR,R0 000104' 013701 172006 MOV @#YSR,R1 ; and start display processor again ASAP 000110' 012714 000001 MOV #1,@R4 000114' 042700 176000 BIC #176000,R0 ; mask out the X position from bits 0..9 000120' 060037 000072' ADD R0,@#XACC 000124' 042701 176000 BIC #176000,R1 ; mask out the Y position from bits 0..9 000130' 060137 000074' ADD R1,@#YACC 000134' 005237 000076' INC @#NHIT 000140' 000002 RTI ; all done. should have got up to 8 light pen hits during a single display 000142' STOPINTR: 000142' 016701 177730 MOV NHIT,R1 000146' 001422 BEQ ENDINTR 000150' 016700 177716 MOV XACC,R0 000154' 004767 000040 JSR PC,DIVIDE 000160' 010037 000302' MOV R0,@#CX 000164' 013700 000074' MOV @#YACC,R0 000170' 004767 000024 JSR PC,DIVIDE 000174' 010037 000304' MOV R0,@#CY 000200' 005067 177666 CLR XACC 000204' 005067 177664 CLR YACC 000210' 005067 177662 CLR NHIT 000214' ENDINTR: 000214' 010514 MOV R5,@R4 ; continue 000216' 000002 RTI ; R0 := R0 / R1, remainder in R2, R1 is positivised ; R0 is top, shifted into R2 one bit at a time. ; R3 is the loop counter. 000220' DIVIDE: 000220' 010246 MOV R2,-(SP) 000222' 010346 MOV R3,-(SP) 000224' 005701 TST R1 ; Validate divisor 000226' 001421 BEQ DIV0 ; divide by 0! 000230' 100001 BPL DIV1 000232' 005401 NEG R1 000234' DIV1: 000234' 005002 CLR R2 000236' 012703 000017 MOV #15.,R3 ; 16 iterations 000242' DIV2: 000242' 006300 ASL R0 000244' 006102 ROL R2 000246' 020201 CMP R2,R1 ; can we subtract bottom from top? 000250' 103403 BCS DIV3 ; no 000252' 160102 SUB R1,R2 ; yes - do it. 000254' 052700 000001 BIS #1,R0 000260' 005303 DIV3: DEC R3 000262' 100367 BPL DIV2 000264' 012603 DIVEND: MOV (SP)+,R3 000266' 012602 MOV (SP)+,R2 000270' 000207 RTS PC 000272' DIV0: ; divide by 0. return 0. (any other ideas?) 000272' 005000 CLR R0 000274' 000773 BR DIVEND ; end of DIVIDE 000276' 170200 DPROG: STATSA+LPLITE ; Values to change the position by one gooby 004000 DX = 4000 000020 DY = 20 000300' 114140 DLOOP: POINT+LPON 000302' 001000 CX: WIDTH/2 ; start in the middle 000304' 000600 CY: HEIGHT/2 ; draw 8 radial lines 000306' 107600 SHORTV+INT7 000310' 170004 STATSA+SYNC ; to avoid too-quick refresh 000312' 024040 MISVX+DX+DY+DY ; top left (-1,+2) ... 000314' 044140 INTX+DX+MISVY+DY+DY ; ... and draw to centre 000316' 004040 DX+DY+DY ; top right(+1,+2) 000320' 064140 INTX+MISVX+DX+MISVY+DY+DY 000322' 010020 DX+DX+DY ; right top (+2,+1) 000324' 070120 INTX+MISVX+DX+DX+MISVY+DY 000326' 010120 DX+DX+MISVY+DY ; right bottom (+2,-1) 000330' 070020 INTX+MISVX+DX+DX+DY 000332' 004140 DX+MISVY+DY+DY ; bottom right (+1,-2) 000334' 064040 INTX+MISVX+DX+DY+DY 000336' 024140 MISVX+DX+MISVY+DY+DY ; bottom left (-1,-2) 000340' 044040 INTX+DX+DY+DY 000342' 030120 MISVX+DX+DX+MISVY+DY ; left bottom (-2,-1) 000344' 050020 INTX+DX+DX+DY 000346' 030020 MISVX+DX+DX+DY ; left top (-2,+1) 000350' 050120 INTX+DX+DX+MISVY+DY 000352' 173400 DSTOP 000354' 160000 DJMP 000356' 000300' DLOOP .END No errors detected Assembly statistics (words): Absolute Relocatable Code 0 120 Reloc. info 0 11 Space used for symbol table: 1105 words Total workspace used: 1337 words Assembly complete