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From: ee@datcon.co.uk (Eddie Edwards) Subject: Article: Hardware Scrolling Summary: Hardware Scrolling using VIDC and MEMC Keywords: VIDC MEMC Acorn Archimedes Games Scrolling Sad Date: Thu, 3 Feb 1994 18:50:50 GMT Hardware Scrolling using VIDC and MEMC Author : Eddie Edwards (ee@datcon.co.uk) Version: 0.1 Date : 03/02/94 It is possible, on a system which uses the VIDC and MEMC chips, to perform scrolling in hardware in all four directions (and combinations thereof). This is possible to single pixel resolution in the vertical direction and double pixel resolution in the horizontal direction. This article attempts to explain the method, give all the technical detail required, and includes a limited implementation as a scrolltext demo. [-----------------------------------------------------------------------------] THE VIDEO DISPLAY There are four parameters which we are concerned with for the video display, horizontal border start, horizontal border width, horizontal display start and horizontal display width. The meaning of these is explained below by means of a diagram: HSYNC (leading edge) HSYNC : : : : : |----------------------------------------------------| : : |''''''''''''''''''''''''''''''''''''''''''''''''''''| : : |''''''''''''''''''''''''''''''''''''''''''''''''''''| : : |''''''''''''''''''''''''''''''''''''''''''''''''''''| : : |''''X------------------------------------------|''''| : : |''''| |''''| : : |''''| |''''| : : |''''| |''''| : : |''''| |''''| : : |''''| |''''| : : |''''| |''''| : : |''''| |''''| : : |''''| |''''| : : |''''| |''''| : : |''''| |''''| : : |''''| |''''| : : |''''| |''''| : : |''''| |''''| : : |''''| |''''| : : |''''| |''''| : : |''''|------------------------------------------|''''| : : |'''':'''''''''''''''''''''''''''''''''''''''''':''''| : : |'''':'''''''''''''''''''''''''''''''''''''''''':''''| : : |'''':'''''''''''''''''''''''''''''''''''''''''':''''| : : |----:------------------------------------------:----| : : : : : : : : : : : : : 1 <--> : : : 2 <-------------------------------------------------------> 3 <-------> : 4 <--------------------------------------------------> 1 - Horizontal border start (VIDC register &88) 2 - Horizontal border end (VIDC register &94) 3 - Horizontal display start (VIDC register &8C) 4 - Horizontal display end (VIDC register &90) These four parameters (together with two which define the width of the HSYNC pulse and the distance between HSYNC pulses) define the appearance of the screen in the horizontal direction. The parameters are in units of 2 pixels, that is if you increase horizontal display start by 1, the display becomes 2 pixels wider. [HSYNC is the Horizontal SYNC pulse, which occurs when the electron beam of the monitor has traced far enough to the right, and tells it to return to the left of the monitor. Thus, we can imagine that the HSYNC line above is a point on the extreme left of the monitor, usually hidden behind the case. Then the registers above are thought of in terms of how many pixels there are between this point and the point on the display where the border starts, etc.] Usually parameters 1-4 are set up to give a display as above, with a border and a display embedded within the border. One further point to note: the number of bytes read in per line (i.e. 320 for mode 13) is the number of pixels between horizontal display start and end. Therefore these always have to be a fixed number apart. [-----------------------------------------------------------------------------] SCREEN MEMORY We are also interested in one parameter in the MEMC, the screen base address (called Vinit in the VLSI manual). This is different to the screen memory base address, which is fixed by the amount of screen memory you have. The screen base address is the point X on the diagram above, and is the address on the first byte to be output - i.e. the address of the pixel in the top left-hand corner of the display. [-----------------------------------------------------------------------------] HARDWARE SCROLLING THE EASY WAY If we could set Vinit (X on the diagram) to whatever pixel we wanted, we'd have no problem scrolling the screen. However, because of the way the MEMC works (DMA accesses are done 16 bytes at a time into the VIDC, and these 16 bytes have to be on an address &xxxxxx0) Vinit can only be set to multiples of 16 bytes. What this does mean, though, is that vertical scrolling is easy. Merely add or subtract the width of a line (e.g. 320 bytes in mode 13) to the current Vinit. Obviously, we update the register just after a VSYNC, or OS_Byte 19, so the screen doesn't flicker, and we must make sure beforehand that the bottom/top line of the screen (the one which will come into view) is set up with whatever graphics we want to display. [-----------------------------------------------------------------------------] HARDWARE SCROLLING THE HARD WAY The climax of the article - how do we do horizontal scrolling? Well, if we want to scroll 16 bytes at a time, we can do that in the same way as above. But we probably want a finer granularity than that. To achieve this, we cheat. Say we want to scroll the screen left by two pixels at a time (and as will be apparent from the method, the screen can only be scrolled two pixels at a time horizontally). What we do is move the horizontal display start and horizontal display end registers left by two pixels (i.e. subtract 1 from both registers). This makes the part of the screen we are looking at move left, i.e. the screen scrolls left ... or at least it would, except it looks like it's just moved. When we have moved the display left by 14 pixels and want to scroll again, NOW we can update Vinit in the MEMC, and put the display back at offset 0. To turn this into the illusion of scrolling, we start playing with the border start and end registers. The thing is, before the border starts only blackness is displayed. After the border starts but before the display starts, the border colour is shown, and after the display and border have started the display is shown. However, until the border has started, nothing is EVER displayed. So if we start the border after we start the display, we lose the border, but we get to chop off the bit of the display we don't want. So we set the border start register to the normal display start (i.e. the right-most point that display start ever touches) and set the border end register to the normal display end - 14 pixels (i.e. the left-most point that display end ever touches). This means that we get blackness, then the part of the display we want to show, then blackness. It also means that we have a method for horizontal scrolling in hardware. The apparent screen size, however, is 14 pixels less than the actual screen size. If we want an apparent screen size of 320 pixels, we just define a screen 334 pixels wide. Simple! The extra 14 bytes per line are used before scrolling to insert what we're scrolling onto the screen. [-----------------------------------------------------------------------------] PROGRAMMING THE VIDC The VIDC is programmed by writing words, which contain the register to be programmed and the value in one word, to the VIDC chip, at address &3400000. The top byte of the word is the register number, the bottom three bytes contain the value, in a position which changes for each register. The four registers which concern us are shown below: =============================================================================== Horizontal Border Start (&88) If M pixels are required between the start of the HSYNC pulse and the start of the border, program (M-1)/2 into this register. (M is odd). The value of the word to be written is then &88000000 + (v<<14) where v is the value calculated =============================================================================== Horizontal Display Start (&8C) If M pixels are required between the start of the HSYNC pulse and the start of the display, program (M-5)/2 for 256-colour modes, (M-7)/2 for 16 colour modes, (M-11)/2 for 4 colour modes and (M-19)/2 for 2 colour modes. (M is odd). The value of the word to be written is then &8C000000 + (v<<14) where v is the value calculated =============================================================================== Horizontal Display End (&90) If M pixels are required between the start of the HSYNC pulse and the end of the display, program (M-5)/2 for 256-colour modes, (M-7)/2 for 16 colour modes, (M-11)/2 for 4 colour modes and (M-19)/2 for 2 colour modes. (M is odd). The value of the word to be written is then &90000000 + (v<<14) where v is the value calculated =============================================================================== Horizontal Border End (&94) If M pixels are required between the start of the HSYNC pulse and the end of the border, program (M-1)/2 into this register. (M is odd). The value of the word to be written is then &94000000 + (v<<14) where v is the value calculated =============================================================================== To set up the mode required initially, change to a normal mode with similar characteristics and merely change the registers above. Note that you cannot rely on an OS plotting calls working. Note further that you can only write to the VIDC and MEMC in SUPERVISOR mode. I.E. call OS_EnterOS before starting all this scrolling stuff. [-----------------------------------------------------------------------------] PROGRAMMING THE MEMC The MEMC is programmed by writing anything to certain addresses, which are at the extreme top of the memory map. (Note that writing to anywhere between &3400000 and &35FFFFF activates the VIDC, which reads data off the bus, so this is "where" the VIDC resides for any MEMC-based system) The MEMC handles all DMA accesses within the system, which can only be in the bottom 512K of RAM. This PHYSICALLY resides at addresses &2000000 onwards, but the LOGICAL addresses are laid out (by RISC-OS) so that however much video memory is allocated, it LOGICALLY ends at &20000000 and starts at &20000000 - (size of video buffer). This means that a Supervisor mode program can do circular WRITES of the video buffer, by starting in logical RAM and crossing the boundary into the physical RAM. Most useful. The key thing to remember, though, is that all numbers used in the MEMC are offsets from the start of video memory. What happens when a screen is drawn is that after a VSYNC, the video pointer is set to Vinit. There are two other registers which define the buffer - Vstart and Vend. If Vptr ever increases past Vend, it is automatically initialised to Vstart. Typically, Vstart will be 0 and Vend will be the size of video memory you have allocated, although there is no reason why you shouldn't change this. Vinit is the start of the screen, as explained above. All three registers can only be programmed to multiples of 16 bytes. To calculate the address to write to, Vinit = &3600000+(val>>4)<<2 Vstart = &3620000+(val>>4)<<2 Vend = &3640000+(val>>4)<<2 Then you merely do a STR Rx,[address] to set the register to that value. Note, however, that OS_Word 22 will set Vinit for you, and OS_UpdateMEMC allows you to change the control register (the interesting bit in that is the one which turns video DMA on and off - turning it off speeds the program up and gives a completely black screen). These calls are used by the demo below. (BTW: The address in the scrolltext is no longer my residence ... oddly :-) [-----------------------------------------------------------------------------] Thanks to: Paul Dellar, for outlining the algorithm, The VLSI Manual, for being there :-) &c &c &c Any corrections, suggestions etc. to ee@datcon.co.uk Hope this is useful, Happy scrolling! Eddie xxx [-----------------------------------------------------------------------------] 10 REM >Isometric4 20 DIM code% 65536*2 30 FOR i%=0 TO 2 STEP 2 40 P%=code% 50 [OPT i% 60 FNlocdeloc(i%,demo,&1FEC000) 70 .generate 80 ADR R1,block:MOV R0,#10:SWI "OS_Word" 90 LDR R0,buffad2:ADD R1,R0,#3456:LDR R2,buffad:ADD R3,R2,#3456 100 STR R0,buffad:STR R2,buffad2 110 MOV R4,#0:MOV R5,#0 120 MOV R8,#0:MOV R9,#0 130 MVN R6,#0:MVN R7,#0 140 MVN R10,#0:MVN R11,#0 150 MOV R12,#3456 160 .loopgen1 170 STMIA R0!,{R4-R5,R8-R9}:STMIA R1!,{R6-R7,R10-R11} 180 STMIA R0!,{R4-R5,R8-R9}:STMIA R1!,{R6-R7,R10-R11} 190 STMIA R0!,{R4-R5,R8-R9}:STMIA R1!,{R6-R7,R10-R11} 200 STMIA R0!,{R4-R5,R8-R9}:STMIA R1!,{R6-R7,R10-R11} 210 STMIA R0!,{R4-R5,R8-R9}:STMIA R1!,{R6-R7,R10-R11} 220 STMIA R0!,{R4-R5,R8-R9}:STMIA R1!,{R6-R7,R10-R11} 230 STMIA R0!,{R4-R5,R8-R9}:STMIA R1!,{R6-R7,R10-R11} 240 STMIA R0!,{R4-R5,R8-R9}:STMIA R1!,{R6-R7,R10-R11} 250 SUBS R12,R12,#128:BNE loopgen1 260 STMFD R13!,{R14} 270 LDR R0,buffad:ADD R0,R0,#1536+48*4+32 280 ADR R1,char+4 290 MOV R6,#8 300 LDR R7,thick 310 .loopgen2 320 MOV R2,#1 330 MOV R5,R0 340 MOV R3,#8 350 LDRB R4,[R1],#-1 360 .loopgen3 370 TST R4,R2:BEQ nodraw 380 BL putblk 390 ADD R0,R0,#100 400 CMP R7,#2 410 BLEQ putblk 420 SUB R0,R0,#100 430 .nodraw 440 ADD R0,R0,#92 450 MOV R2,R2,ASL #1 460 SUBS R3,R3,#1:BNE loopgen3 470 MOV R0,R5 480 SUB R0,R0,#48*5 490 SUBS R6,R6,#1 500 BNE loopgen2 510 LDMFD R13!,{PC} 520 .thick EQUD 2 530 .gen_part2 540 LDR R2,buffad:LDR R0,buffad2:ADD R0,R0,#32:ADD R2,R2,#48*16 550 ADD R1,R0,#3456 560 MOV R4,#56 570 .loopgen4 580 LDMIA R2,{R5-R8} 590 LDMIA R1,{R9-R12} 600 AND R5,R5,R9:AND R6,R6,R10 610 AND R7,R7,R11:AND R8,R8,R12 620 LDMIA R0,{R9-R12} 630 ORR R5,R5,R9:ORR R6,R6,R10 640 ORR R7,R7,R11:ORR R8,R8,R12 650 STMIA R2,{R5-R8} 660 ADD R0,R0,#48:ADD R2,R2,#48:ADD R1,R1,#48 670 SUBS R4,R4,#1:BNE loopgen4 680 MOV PC,R14 690 .thick1 MOV R0,#1:STR R0,thick:B nextchr 700 .thick2 MOV R0,#2:STR R0,thick:B nextchr 710 .putblk ADR R8,grafix:MOV R9,#10:MOV R10,R0 720 .loopPB1 730 LDR R11,[R10,#3456]:LDR R12,[R8,#8]:AND R11,R11,R12:STR R11,[R10,#3456] 740 LDR R11,[R10]:LDR R12,[R8,#8]:AND R11,R11,R12:LDR R12,[R8],#4:ORR R11,R11,R12:STR R11,[R10],#4 750 LDR R11,[R10,#3456]:LDR R12,[R8,#8]:AND R11,R11,R12:STR R11,[R10,#3456] 760 LDR R11,[R10]:LDR R12,[R8,#8]:AND R11,R11,R12:LDR R12,[R8],#12:ORR R11,R11,R12:STR R11,[R10],#44 770 SUBS R9,R9,#1:BNE loopPB1 780 MOV PC,R14 790 .trans 800 ADR R0,grafixO 810 ADR R5,grafix 820 LDR R1,conv 830 MOV R2,#160 840 .loopT 850 LDRB R3,[R0],#1 860 CMP R3,#255:MOVEQ R3,#4 870 LDRB R4,[R1,R3] 880 STRB R4,[R5],#1 890 SUBS R2,R2,#1 900 BNE loopT 910 MOV PC,R14 920 .conv EQUD conv1 930 .conv1 EQUB 0 940 EQUB &13 950 EQUB &07 960 EQUB &77 970 EQUB &FF 980 ALIGN 990 .conv2 EQUB 0 1000 EQUB &13 1010 EQUB &07 1020 EQUB &63 1030 EQUB &FF 1040 ALIGN 1050 .conv3 EQUB 0 1060 EQUB &13 1070 EQUB &07 1080 EQUB &8B 1090 EQUB &FF 1100 ALIGN 1110 .conv4 EQUB 0 1120 EQUB &13 1130 EQUB &07 1140 EQUB &2F 1150 EQUB &FF 1160 ALIGN 1170 .conv5 EQUB 0 1180 EQUB &13 1190 EQUB &07 1200 EQUB &FF 1210 EQUB &FF 1220 ALIGN 1230 .conv9 EQUB 0 1240 EQUB &13 1250 EQUB &07 1260 EQUB &17 1270 EQUB &FF 1280 ALIGN 1290 .comm1 ADR R1,conv1:STR R1,conv:BL trans:B nextchr 1300 .comm2 ADR R1,conv2:STR R1,conv:BL trans:B nextchr 1310 .comm3 ADR R1,conv3:STR R1,conv:BL trans:B nextchr 1320 .comm4 ADR R1,conv4:STR R1,conv:BL trans:B nextchr 1330 .comm5 ADR R1,conv5:STR R1,conv:BL trans:B nextchr 1340 .comm9 ADR R1,conv9:STR R1,conv:BL trans:B nextchr 1350 .grafix 1360 EQUD &01000000:EQUD &00000001:EQUD &00FFFFFF:EQUD &FFFFFF00 1370 EQUD &01010100:EQUD &00010101:EQUD &000000FF:EQUD &FF000000 1380 EQUD &01010101:EQUD &01010101:EQUD &00000000:EQUD &00000000 1390 EQUD &01010102:EQUD &03010101:EQUD &00000000:EQUD &00000000 1400 EQUD &01020202:EQUD &03030301:EQUD &00000000:EQUD &00000000 1410 EQUD &02020202:EQUD &03030303:EQUD &00000000:EQUD &00000000 1420 EQUD &02020202:EQUD &03030303:EQUD &00000000:EQUD &00000000 1430 EQUD &02020202:EQUD &03030303:EQUD &00000000:EQUD &00000000 1440 EQUD &02020200:EQUD &00030303:EQUD &000000FF:EQUD &FF000000 1450 EQUD &02000000:EQUD &00000003:EQUD &00FFFFFF:EQUD &FFFFFF00 1460 .grafixO 1470 EQUD &01000000:EQUD &00000001:EQUD &00FFFFFF:EQUD &FFFFFF00 1480 EQUD &01010100:EQUD &00010101:EQUD &000000FF:EQUD &FF000000 1490 EQUD &01010101:EQUD &01010101:EQUD &00000000:EQUD &00000000 1500 EQUD &01010102:EQUD &03010101:EQUD &00000000:EQUD &00000000 1510 EQUD &01020202:EQUD &03030301:EQUD &00000000:EQUD &00000000 1520 EQUD &02020202:EQUD &03030303:EQUD &00000000:EQUD &00000000 1530 EQUD &02020202:EQUD &03030303:EQUD &00000000:EQUD &00000000 1540 EQUD &02020202:EQUD &03030303:EQUD &00000000:EQUD &00000000 1550 EQUD &02020200:EQUD &00030303:EQUD &000000FF:EQUD &FF000000 1560 EQUD &02000000:EQUD &00000003:EQUD &00FFFFFF:EQUD &FFFFFF00 1570 .block EQUD 69 1580 .char EQUD 0:EQUD 0 1590 .count EQUD 0 1600 .countapply EQUD buffer 1610 .buffad EQUD buffer 1620 .buffad2 EQUD buffer+6912 1630 EQUB 0:EQUB 0:EQUB 0 1640 .parablock EQUB 3 1650 .screenoff EQUD 0 1660 .screenstartabs EQUD &1FEC000 1670 .screenstart EQUD &1FEC000 1680 1681 ; main scroll routine - only scrolls left and down for the minute 1690 1700 .scrollLEFTword 1710 MOV R0,#19:SWI "OS_Byte" ; VSYNC 1720 SWI 22 ; OS_EnterOS - need 1730 MOVNV R0,R0 ; Supervisor mode for this! 1740 LDR R11,screenstartabs:RSB R11,R11,#&2000000 ; R11 = screen buf size 1750 LDR R0,screenstart:ADD R0,R0,#4 ; move screenstart 4 right 1760 SUB R0,R0,#640 ; and 2 up 1770 CMP R0,#&2000000:SUBHS R0,R0,R11 ; make sure it's in the 1771 ; screen buffer 1780 LDR R1,screenstartabs ; make sure it's in the 1790 CMP R0,R1:ADDLO R0,R0,R11 ; screen buffer 1800 STR R0,screenstart ; and update variable 1810 MOV R2,R0,LSR #1:AND R2,R2,#6 ; get pixels/2 across 1811 ; from window 1812 ; (shift of 0-7) 1820 RSB R2,R2,#66 ; calc. timing from left 1821 ; HSYNC 1830 MOV R2,R2,ASL #14 ; shift into VIDC format 1840 ORR R2,R2,#&8C000000:MOV R1,#&03400000 ; get VIDC reg no, 1850 STR R2,[R1] ; store! 1860 ADD R2,R2,#&04000000 ; get right side reg 1870 ADD R2,R2,#&00280000:STR R2,[R1] ; add size of screen & 1871 ; store 1880 MOV R2,#(68<<14):ORR R2,R2,#&88000000:STR R2,[R1] ; border offset L ... 1890 ADD R2,R2,#(320-12)<<13:ADD R2,R2,#&0C000000:STR R2,[R1] ; and right 1900 LDR R1,screenoff ; get screen offset 1910 TST R0,#15 ; if screenstart is 0 MOD 16 1920 ADDEQ R1,R1,#16 ; then add 16 to screen off 1930 SUBS R1,R1,#640:ADDMI R1,R1,R11 ; sub 640 (2 lines) and 1931 ; realign if overflow off 1932 ; screen base 1940 CMP R1,R11:SUBHS R1,R1,R11:STR R1,screenoff ; then update variable 1950 MOV R0,#22:ADR R1,parablock:SWI "OS_Word" ; update MEMC screen addr 1960 LDR R0,screenstart ; get screenstart 1970 SUB R0,R0,#4 ; sub 4 1980 LDR R1,screenstartabs ; get top of screen mem 1990 CMP R0,R1:ADDLO R0,R0,R11 ; align screenstart 2000 STMFD R13!,{R0} ; save 2010 LDR R9,offsetr ; rest is scrolling code 2020 LDR R8,count:MOV R8,R8,LSR #1:ADD R8,R8,R9 ; to print the invisible 2030 MOV R11,R8 ; line for the next time 2040 MOV R1,#0 ; around .... 2050 .loopP1 2060 STR R1,[R0],#320:SUBS R8,R8,#1:BNE loopP1 2070 LDR R8,count:LDR R9,countapply:ADD R9,R9,R8:ADD R10,R9,#3456 2080 MOV R12,#72 2090 .loopP2 2100 LDR R1,[R9],#48:STR R1,[R0],#320 2110 LDR R1,[R9],#48:STR R1,[R0],#320 2120 LDR R1,[R9],#48:STR R1,[R0],#320 2130 LDR R1,[R9],#48:STR R1,[R0],#320 2140 LDR R1,[R9],#48:STR R1,[R0],#320 2150 LDR R1,[R9],#48:STR R1,[R0],#320 2160 LDR R1,[R9],#48:STR R1,[R0],#320 2170 LDR R1,[R9],#48:STR R1,[R0],#320 2180 SUBS R12,R12,#8:BNE loopP2 2190 ADD R11,R11,#72 2200 MOV R1,#0 2210 .loopP3 2220 STR R1,[R0],#320:ADD R11,R11,#1:CMP R11,#128:BNE loopP3 2230 LDR R1,col1:LDR R2,adder:LDMFD R13!,{R8} 2240 MOV R3,#0:MOV R4,#0:MOV R5,#0:MOV R6,#0 2250 ADD R8,R8,#320 2260 STMIA R8!,{R3-R6}:STMIA R8!,{R3-R6} 2270 STMIA R8!,{R3-R6}:STMIA R8!,{R3-R6} 2280 SUB R8,R8,#384 2290 STMIA R8!,{R3-R6}:STMIA R8!,{R3-R6} 2300 STMIA R8!,{R3-R6}:STMIA R8!,{R3-R6} 2310 .loopP4 2320 STR R1,[R0],#320:TST R11,#1:STRNE R1,[R8,#316]:STREQ R1,[R8],#4:ADD R1,R1,R2:ADD R11,R11,#1:CMP R11,#255:BNE loopP4 2330 MOV R1,R1,ASL #16:MOV R1,R1,LSR #16:STR R1,[R0]:STR R1,[R8,#316] 2340 TEQP PC,#0:MOVNV R0,R0 2350 MOV PC,R14 2360 .col1 EQUD &01010000 2370 .adder EQUD &01010101 2380 .const1 EQUD 320*72 2390 .minispace MOV R0,#8:STR R0,nextcount:B nextchr 2400 .nextcount EQUD 40 2410 .notpending CMP R0,#32 2420 MOVNE PC,R14 2430 STMFD R13!,{R14} 2440 BL gen_part2 2450 MOV R0,#0:STR R0,count 2460 LDR R0,buffad:STR R0,countapply 2470 LDR R0,nextoffsetr:STR R0,offsetr 2480 LDMFD R13!,{PC} 2490 .scroll LDR R0,count:ADD R0,R0,#4 2500 LDR R1,nextcount:CMP R0,R1:MOVEQ R0,#28 2510 STR R0,count 2520 CMP R0,#28:BNE notpending 2530 MOV R1,#40:STR R1,nextcount 2540 STMFD R13!,{R14} 2550 .nextchr 2560 LDR R0,textptr:LDRB R1,[R0],#1:STR R0,textptr 2570 CMP R1,#32:BLO command 2580 STR R1,block 2590 BL generate 2600 LDMFD R13!,{PC} 2610 .command CMP R1,#12:BHI nextchr 2620 ADD PC,PC,R1,ASL #2 2630 B nextchr 2640 B resettext 2650 B comm1 2660 B comm2 2670 B comm3 2680 B comm4 2690 B comm5 2700 B thick1 2710 B thick2 2720 B offset 2730 B comm9 2740 B minispace 2750 B slow 2760 B fast 2770 .offset LDR R0,textptr:LDRB R1,[R0],#1:STR R0,textptr 2780 STR R1,nextoffsetr 2790 B nextchr 2800 .offsetr EQUD 20 2810 .nextoffsetr EQUD 20 2820 .resettext 2830 LDR R0,textinit:STR R0,textptr:B nextchr 2840 .demo 2850 STMFD R13!,{R14} 2860 SWI &116:SWI &10D:SWI "OS_RemoveCursors" 2870 MOV R0,#0:MOV R1,#1024:SWI "OS_UpdateMEMC" ; screen off 2880 MOV R0,#100 2890 .loopdemo1 2900 STMFD R13!,{R0} 2910 BL scrollLEFTword+8 ; scroll without waiting 2920 BL scrollLEFTword+8 ; for VSYNC - this fills 2930 BL scrollLEFTword+8 ; the screen with the 2940 BL scrollLEFTword+8 ; background 2950 LDMFD R13!,{R0} 2960 SUBS R0,R0,#4:BNE loopdemo1 2970 MOV R0,#19:SWI "OS_Byte" ; wait a little while 2980 MOV R0,#19:SWI "OS_Byte" 2990 MOV R0,#19:SWI "OS_Byte" 3000 MOV R0,#19:SWI "OS_Byte" 3010 MOV R0,#19:SWI "OS_Byte" 3020 MOV R0,#19:SWI "OS_Byte" 3030 MOV R0,#19:SWI "OS_Byte" 3040 MOV R0,#19:SWI "OS_Byte" 3050 MOV R0,#19:SWI "OS_Byte" 3060 MOV R0,#19:SWI "OS_Byte" 3070 MOV R0,#1024:MOV R1,#1024:SWI "OS_UpdateMEMC" ; screen on 3080 BL music ; (music on) 3090 .loopdemo 3100 BL scroll ; calc 3110 BL scrollLEFTword ; scroll 3120 LDR R0,speed:CMP R0,#2:BNE notfast 3130 BL scroll ; calc some more 3140 BL scrollLEFTword+8 ; scroll without VSYNC 3150 .notfast 3160 BL music+4 ; update music 3170 MOV R0,#129:MOV R1,#0:MOV R2,#0:SWI "OS_Byte" ; get ESCAPE 3180 CMP R2,#27:BNE loopdemo ; if not, loop 3190 BL music+8 ; kill music 3200 LDMFD R13!,{PC} ; die 3210 .slow MOV R0,#1:STR R0,speed:B nextchr 3220 .fast MOV R0,#2:STR R0,speed:B nextchr 3230 .speed EQUD 1 3240 .textptr EQUD text 3250 .textinit EQUD realtext 3260 .text 3270 EQUS " " 3280 .realtext 3290 EQUB 1:EQUB 7:EQUB 8:EQUB 20 3300 EQUS "Welcome to ........ " 3310 EQUB 5:EQUS "Crap Demo #3":EQUB 1:EQUS " !!!!! " 3320 EQUS "Written by " 3330 EQUB 6:EQUB 2:EQUS "Mike Edwards":EQUB 7:EQUB 1 3340 EQUS ", for a " 3350 EQUB 9 3360 EQUB 8:EQUB 20:EQUS "L":EQUB 10:EQUB 32 3370 EQUB 8:EQUB 4:EQUS "A":EQUB 10:EQUB 32 3380 EQUB 8:EQUB 20:EQUS "U":EQUB 10:EQUB 32 3390 EQUB 8:EQUB 36:EQUS "G":EQUB 10:EQUB 32 3400 EQUB 8:EQUB 20:EQUS "H":EQUB 10:EQUB 32 3410 EQUB 1 3420 EQUS " on the 27th of December " 3430 EQUS "1990, using lots of dodgy programming techniques, etc. " 3440 EQUS "Every 50th of a second, the screen is scrolling in this direction " 3450 EQUS "and a strip of letter is added onto the right-hand end. These " 3460 EQUS "strips are calculated letter by letter, behind the previous letter " 3470 EQUS "and then plotted. The big letters are not kept in memory (a full " 3480 EQUS "character set would take 576K!!!) but calculated from the system " 3490 EQUS "font. Hence, to change this font all you have to do is change the " 3500 EQUS "system font!!! Also, I'm not using any " 3510 EQUB 4:EQUS "shadow":EQUB 1 3520 EQUS " screens. At the end of this scrolltext, I'll print all 224 " 3530 EQUS "characters, just to prove that I'm not storing them (this would " 3540 EQUS "take 1344K!). The calculation is split up into two halves, one " 3550 EQUS "just before a character is needed and one when it is " 3560 EQUS "needed (the complete calculation takes too long, and there's all " 3570 EQUS "this time going spare between letters! Anyway, I'd better be " 3580 EQUS "going as it's now the 28th of December (i.e. past bedtime!) and " 3590 EQUS "I'm bored of writing this scrolltext. Write to : " 3600 EQUB 5:EQUS "Mike ":EQUB 9:EQUS """Eddie""":EQUB 5 3610 EQUS " Edwards, Christ's College, Cambridge ":EQUB 1 3620 EQUS " Lots of love and kisses, Eddie xxx Now here's the entire " 3630 EQUS "character set (as promised): " 3640 EQUB 3:EQUB 12:EQUB 6 3650 .chrsetentire 3660 ] 3670 P%+=224 3680 [OPT i% 3690 EQUS " " 3700 EQUB 11:EQUB 7 3710 EQUB 1 3720 EQUS " Time to replay ... " 3730 EQUB 0 3740 ALIGN 3750 .buffer 3760 ] 3770 P%+=3456*4 3780 [OPT i% 3790 .music 3800 MOV PC,R14 3810 MOV PC,R14 3820 MOV PC,R14 3830 ] 3840 NEXT 3850 FOR i%=0 TO 3455 STEP 4 3860 buffer!i%=0:buffer!(i%+3456)=-1 3870 NEXT 3880 FOR i%=0 TO 223:chrsetentire?i%=i%+32:NEXT 3890 CALL delocate 3900 OSCLI("Save CrapDemo3 "+STR$~code%+" "+STR$~P%) 3910 OSCLI("Settype CrapDemo3 Absolute") 3920 CALL locate 3930 CALL demo 3940 END 3950 REM >%.Assemprims.LocDeloc 3960 DEF FNlocdeloc(opt%,maincode%,video%) 3970 [OPT opt% 3980 .top 3990 SWI "OS_GetEnv" 4000 MOV R13,R1 4010 BL locate 4020 BL maincode% 4030 BL delocate 4040 SWI "OS_Exit" 4050 .locate 4060 SWI &116:SWI &100:SWI "OS_RemoveCursors" 4070 ADR R0,list:ADR R1,vdu 4080 SWI "OS_ReadVduVariables" 4090 ADR R0,top:ADR R1,vidlist:LDR R2,vdu 4100 .loopL1 4110 LDR R3,[R1],#4:CMP R3,#0:BEQ nextbitL 4120 ADD R3,R3,R0:LDR R4,[R3]:ADD R4,R4,R2:STR R4,[R3] 4130 B loopL1 4140 .nextbitL 4150 ADR R1,EQUDlist 4160 .loopL2 4170 LDR R3,[R1],#4:CMP R3,#0:MOVEQ PC,R14 4180 ADD R3,R3,R0:LDR R4,[R3]:ADD R4,R4,R0:STR R4,[R3] 4190 B loopL2 4200 .list EQUD 149:EQUD -1 4210 .vdu EQUD video% 4220 .delocate 4230 ADR R0,top:ADR R1,vidlist:LDR R2,vdu 4240 .loopDL1 4250 LDR R3,[R1],#4:CMP R3,#0:BEQ nextbitDL 4260 ADD R3,R3,R0:LDR R4,[R3]:SUB R4,R4,R2:STR R4,[R3] 4270 B loopDL1 4280 .nextbitDL 4290 ADR R1,EQUDlist 4300 .loopDL2 4310 LDR R3,[R1],#4:CMP R3,#0:MOVEQ PC,R14 4320 ADD R3,R3,R0:LDR R4,[R3]:SUB R4,R4,R0:STR R4,[R3] 4330 B loopDL2 4340 .vidlist 4350 EQUD screenstartabs-top 4360 EQUD screenstart-top 4370 EQUD 0 4380 .EQUDlist 4390 EQUD conv-top 4400 EQUD countapply-top 4410 EQUD buffad-top 4420 EQUD buffad2-top 4430 EQUD textptr-top 4440 EQUD textinit-top 4450 EQUD 0 4460 ] 4470 =0