Disassembling the VDPTEST program for the Third Millenium Enginnering Arcade Board

So I thought I'd have a look at what the VDPTEST program actually does.

Doing a PR#1 and LOAD VDPTEST and LIST gets me:

]LOAD VDPTEST
]LIST

10  REM  SLOT FINDER ROUTINE
20  FOR S = 7 TO 1 STEP  - 1
30 RD = 49280 + S * 16
40 RS = 49281 + S * 16
50 WD = 49282 + S * 16
60 WR = 49283 + S * 16
100 A =  INT ( RND (1) * 256)
110 B =  INT ( RND (1) * 256)
120 C =  INT ( RND (1) * 256)
130  POKE WR,0: POKE WR,64
140  POKE WD,A: POKE WD,B: POKE WD,C
150  POKE WR,0: POKE WR,0
155 T = S
160  IF  PEEK (RD) = A AND  PEEK (RD) = B AND  PEEK (RD) = C THEN S = 1
170  NEXT S
180  PRINT  CHR$ (4)"BLOAD VDPTST"
190 N = 129 + T * 16
200  POKE 4107,N: POKE 4112,N: POKE 4118,N - 1: POKE 4132,N: POKE 4135,N: POKE 4142,N - 1
210 C = 0
220 D =  PEEK (RS)
230  FOR R = 128 TO 135
240  READ D
250  IF D = 256 THEN  RESTORE : READ D
260  POKE WR,D
270  POKE WR,R
280  NEXT R
290 C = C + 1
300  PRINT "LOOP ";C
310  CALL 4096
320  IF  PEEK (8192) = 204 THEN 220
330  PRINT  CHR$ (7);"ERROR AT VRAM ADDRESS ";16384 - 256 * ( PEEK (8195) - 1) -  PEEK (8196)
335  PRINT "DATA WRITTEN: "; PEEK (8194)
340  PRINT "DATA READ:"; PEEK (8193)
345  CALL 768
350  DATA 2,192,6,255,3,56,7,3
355  DATA 2,193,7,127,7,48,7,4
360  DATA 2,194,14,255,3,120,3,6
365  DATA 2,195,15,127,7,112,3,10
370  DATA  256

]BLOAD VDPTST
]CALL -151

*1000L

1000-   A9 00       LDA   #$00
1002-   8D 4C 10    STA   $104C
1005-   A2 40       LDX   #$40
1007-   A0 00       LDY   #$00
1009-   98          TYA   
100A-   8D C1 C0    STA   $C0C1
100D-   A9 40       LDA   #$40
100F-   8D C1 C0    STA   $C0C1
1012-   AD 4C 10    LDA   $104C
1015-   8D C0 C0    STA   $C0C0
1018-   88          DEY   
1019-   D0 FA       BNE   $1015
101B-   CA          DEX   
101C-   D0 F7       BNE   $1015
101E-   A2 40       LDX   #$40
1020-   A0 00       LDY   #$00
1022-   98          TYA   
1023-   8D C1 C0    STA   $C0C1
1026-   8D C1 C0    STA   $C0C1
1029-   EA          NOP   
*L

102A-   EA          NOP   
102B-   EA          NOP   
102C-   EA          NOP   
102D-   AD C0 C0    LDA   $C0C0
1030-   CD 4C 10    CMP   $104C
1033-   D0 11       BNE   $1046
1035-   88          DEY   
1036-   D0 F5       BNE   $102D
1038-   CA          DEX   
1039-   D0 F2       BNE   $102D
103B-   EE 4C 10    INC   $104C
103E-   D0 C5       BNE   $1005
1040-   A9 CC       LDA   #$CC
1042-   8D 00 20    STA   $2000
1045-   60          RTS   
1046-   A9 00       LDA   #$00
1048-   8D 00 20    STA   $2000
104B-   60          RTS   
104C-   00          BRK   
104D-   00          BRK   
*

What you see the basic program do is to BLOAD VDPTST which goes to address $1000 (4096) and it will patch it with the proper io addresses for the slot number. So every occurrence of C0C0 and C0C1 will get patched.

It will CALL 4096 after the patching and it writes the entire 16K ($4000) of the TMS9918 with the value held in memory location $104C and then reads it back, comparing it to what's in $104C.

If it gets an error, it writes $00 to address $2000 (8192), but if everything is cool it writes $CC to address $2000 (8192).

What is complete BS is the error reporting in the basic program. It looks for error information at 8193, 8194, 8195 and 8196, but quite frankly I don't see where it's getting this information, because the assembly program just doesn't write those locations. There should be an STX $2003, an STY $2004 or something.

It'll tell you there's an error, but the information reported is bogus.

I kept trying to figure out what the CALL 768 does. The CALL 768 in the program is setup in the HELLO program on the disk. It just resets the apple video output on reset according to the REM remarks.

]LOAD HELLO
]LIST

10  REM  SLOT FINDER ROUTINE
20  FOR S = 7 TO 1 STEP  - 1
30 RD = 49280 + S * 16
40 RS = 49281 + S * 16
50 WD = 49282 + S * 16
60 WR = 49283 + S * 16
70 A =  INT ( RND (1) * 256)
80 B =  INT ( RND (1) * 256)
90 C =  INT ( RND (1) * 256)
100  POKE WR,0: POKE WR,64
110  POKE WD,A: POKE WD,B: POKE WD,C
120  POKE WR,0: POKE WR,0
130 T = S
140  IF  PEEK (RD) = A AND  PEEK (RD) = B AND  PEEK (RD) = C THEN S = 1
150  NEXT S
160  REM  ENABLE APPLE VIDEO
170  POKE WR,1: POKE WR,128
180  POKE WR,128: POKE WR,129
190  POKE WR,0: POKE WR,135
200  HOME 
210  PRINT "THIRD MILLENNIUM ENGINEERING CORPORATION"
220  REM  POKE RESET ROUTINE TO ENABLE APPLE VIDEO INTO MEMORY AT $300
230  POKE 1010,0: POKE 1011,3
240  FOR I = 768 TO 799
250  READ J: POKE I,J
260  NEXT I
270 S = T * 16 + 129
280  POKE 769,S
290 S = S + 2
300  POKE 774,S
310  POKE 779,S
320  POKE 782,S
330  POKE 787,S
340  POKE 792,S
350  POKE 797,S
360  POKE 800,208: POKE 801,3
370  POKE 1012,166
375  PRINT  CHR$ (4)"RUN READ ME"

380  DATA  173,0,192,169,1,141,0,192
390  DATA  169,128,141,0,192,141,0,192
400  DATA  169,129,141,0,192,169,0
410  DATA  141,0,192,169,135,141,0,192,76

]CALL -151

*300L

0300-   AD C1 C0    LDA   $C0C1
0303-   A9 01       LDA   #$01
0305-   8D C3 C0    STA   $C0C3
0308-   A9 80       LDA   #$80
030A-   8D C3 C0    STA   $C0C3
030D-   8D C3 C0    STA   $C0C3
0310-   A9 81       LDA   #$81
0312-   8D C3 C0    STA   $C0C3
0315-   A9 00       LDA   #$00
0317-   8D C3 C0    STA   $C0C3
031A-   A9 87       LDA   #$87
031C-   8D C3 C0    STA   $C0C3
031F-   4C D0 03    JMP   $03D0
0322-   00          BRK   
0323-   00          BRK   
0324-   00          BRK   
0325-   00          BRK   
0326-   00          BRK   
0327-   00          BRK   
0328-   00          BRK   
*

]PR#0

So for fun, I thought I'd patch it by hand with the monitor so it would send the proper values to the basic program if there were an error. There's nothing like changing those values by hand.

I tested it using the mame debugger and changing the values in the TMS9918 vram by hand to simulate a memory error.

What was really driving me crazy is that the basic VDPTEST program kept patching the addresses after I'd changed them. A little "175 GOTO 210" fixed that. I changed the instances of $C0C1 to $C0C3 and $C0C0 to $C0C2 to get it to run under mame 189.

]CALL -151

*1000L

1000-   A9 00       LDA   #$00
1002-   8D 60 10    STA   $1060
1005-   A2 40       LDX   #$40
1007-   A0 00       LDY   #$00
1009-   98          TYA   
100A-   8D C3 C0    STA   $C0C3
100D-   A9 40       LDA   #$40
100F-   8D C3 C0    STA   $C0C3
1012-   AD 60 10    LDA   $1060
1015-   8D C2 C0    STA   $C0C2
1018-   88          DEY   
1019-   D0 FA       BNE   $1015
101B-   CA          DEX   
101C-   D0 F7       BNE   $1015
101E-   A2 40       LDX   #$40
1020-   A0 00       LDY   #$00
1022-   98          TYA   
1023-   8D C3 C0    STA   $C0C3
1026-   8D C3 C0    STA   $C0C3
1029-   EA          NOP   
*L

102A-   EA          NOP   
102B-   EA          NOP   
102C-   EA          NOP   
102D-   AD C0 C0    LDA   $C0C0
1030-   CD 60 10    CMP   $1060
1033-   D0 11       BNE   $1046
1035-   88          DEY   
1036-   D0 F5       BNE   $102D
1038-   CA          DEX   
1039-   D0 F2       BNE   $102D
103B-   EE 60 10    INC   $1060
103E-   D0 C5       BNE   $1005
1040-   A9 CC       LDA   #$CC
1042-   8D 00 20    STA   $2000
1045-   60          RTS   
1046-   8D 01 20    STA   $2001
1049-   8E 03 20    STX   $2003
104C-   8C 04 20    STY   $2004
104F-   AD 60 10    LDA   $1060
1052-   8D 02 20    STA   $2002
*L

1055-   A9 00       LDA   #$00
1057-   8D 00 20    STA   $2000
105A-   60          RTS   
105B-   00          BRK   
105C-   00          BRK   
105D-   00          BRK   
105E-   00          BRK   
105F-   00          BRK   
1060-   00          BRK   
1061-   00          BRK   
1062-   00          BRK   
1063-   00          BRK   
1064-   00          BRK   
1065-   00          BRK   
1066-   00          BRK   
1067-   00          BRK   
1068-   00          BRK   
1069-   00          BRK   
106A-   00          BRK   
106B-   00          BRK