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pcjs/blog/2015/07/14/README.md
Jeff Parsons e76655a48f Fixed I/O port handling
2015-07-15 14:32:20 -07:00

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Windows 95
---
First off, let me just say:
> Happy Windows 95 RTM Day!
because today, July 14, 2015, is the 20th anniversary of Windows 95 RTM ("Release To Manufacturing").
Now, to business. Today is also the first day I tried running Windows 95 SETUP inside a PCjs machine. And it
immediately failed:
Please wait while Setup initializes.
Windows requires a computer with an 80386 processor or higher.
The failing code:
0E36:08FD 06 PUSH ES
0E36:08FE 1E PUSH DS
0E36:08FF 9C PUSHF
0E36:0900 33C0 XOR AX,AX
0E36:0902 50 PUSH AX
0E36:0903 9D POPF
0E36:0904 9C PUSHF
0E36:0905 58 POP AX
0E36:0906 A90080 TEST AX,8000
0E36:0909 7517 JNZ 0922
0E36:090B B80070 MOV AX,7000
0E36:090E 50 PUSH AX
0E36:090F 9D POPF
0E36:0910 FB STI
0E36:0911 9C PUSHF
0E36:0912 58 POP AX
0E36:0913 A90070 TEST AX,7000
0E36:0916 7405 JZ 091D
0E36:0918 B88603 MOV AX,0386
0E36:091B EB08 JMP 0925
0E36:091D B88602 MOV AX,0286
0E36:0920 EB03 JMP 0925
0E36:0922 B88600 MOV AX,0086
0E36:0925 9D POPF
0E36:0926 1F POP DS
0E36:0927 07 POP ES
0E36:0928 C3 RET
was easily fixed with a change to [x86cpu.js](/modules/pcjs/lib/x86cpu.js), allowing the IOPL bits to be
modified in real-mode on an 80386. When I had previously tweaked setPS() to accomodate 80286/80386 discrimination
logic in OS/2 1.0, there was no 80386 support in PCjs at that time, so it was sufficient to *never* allow the
IOPL bits to change in real-mode.
Following the CPU test, Setup proceeded a bit farther:
EAX=00000001 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C33E EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000202 V0 D0 I1 T0 S0 Z0 A0 P0 C0
0E36:0E4F E8D412 CALL 2126 ;cycles=7
0E36:2126 E877E7 CALL 08A0
0E36:2129 0BC0 OR AX,AX
0E36:212B 741D JZ 214A
0E36:212D 6A00 PUSH 0000
0E36:212F 6A00 PUSH 0000
0E36:2131 68C700 PUSH 00C7
0E36:2134 E8C1F8 CALL 19F8
0E36:2137 83C406 ADD SP,0006
EAX=00000001 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C33C EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000202 V0 D0 I1 T0 S0 Z0 A0 P0 C0
0E36:2126 E877E7 CALL 08A0 ;cycles=7
EAX=00000001 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C33A EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000202 V0 D0 I1 T0 S0 Z0 A0 P0 C0
0E36:08A0 56 PUSH SI
EAX=00000001 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C338 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000202 V0 D0 I1 T0 S0 Z0 A0 P0 C0
0E36:08A1 57 PUSH DI ;cycles=3
EAX=00000001 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C336 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000202 V0 D0 I1 T0 S0 Z0 A0 P0 C0
0E36:08A2 B80016 MOV AX,1600 ;cycles=3 (WIN386CHECK)
EAX=00001600 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C336 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000202 V0 D0 I1 T0 S0 Z0 A0 P0 C0
0E36:08A5 CD2F INT 2F ;cycles=2
EAX=00001600 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C336 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000202 V0 D0 I1 T0 S0 Z0 A0 P0 C0
0E36:08A7 A87F TEST AL,7F ;cycles=133
EAX=00001600 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C336 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:08A9 B80300 MOV AX,0003 ;cycles=3
EAX=00000003 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C336 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:08AC 752A JNZ 08D8 ;cycles=2
EAX=00000003 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C336 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:08AE B80A16 MOV AX,160A ;cycles=3 (INSTALLCHECK)
EAX=0000160A EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C336 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:08B1 CD2F INT 2F ;cycles=2
EAX=0000160A EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C336 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:08B3 0BC0 OR AX,AX ;cycles=133
EAX=0000160A EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C336 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000206 V0 D0 I1 T0 S0 Z0 A0 P1 C0
0E36:08B5 740E JZ 08C5 ;cycles=2
EAX=0000160A EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C336 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000206 V0 D0 I1 T0 S0 Z0 A0 P1 C0
0E36:08B7 B88046 MOV AX,4680 ;cycles=3 (WINOLDAP30CHECK)
EAX=00004680 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C336 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000206 V0 D0 I1 T0 S0 Z0 A0 P1 C0
0E36:08BA CD2F INT 2F ;cycles=2
EAX=00004680 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C336 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000206 V0 D0 I1 T0 S0 Z0 A0 P1 C0
0E36:08BC 0BC0 OR AX,AX ;cycles=133
EAX=00004680 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C336 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000202 V0 D0 I1 T0 S0 Z0 A0 P0 C0
0E36:08BE 7516 JNZ 08D6 ;cycles=2
EAX=00004680 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C336 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000202 V0 D0 I1 T0 S0 Z0 A0 P0 C0
0E36:08D6 33C0 XOR AX,AX ;cycles=7
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C336 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:08D8 5F POP DI ;cycles=2
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C338 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:08D9 5E POP SI ;cycles=5
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C33A EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:08DA C3 RET ;cycles=5
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C33C EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:2129 0BC0 OR AX,AX ;cycles=11
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C33C EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:212B 741D JZ 214A ;cycles=2
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C33C EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:214A E88EE7 CALL 08DB ;cycles=7
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C33A EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:08DB 1E PUSH DS ;cycles=7
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C338 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:08DC 06 PUSH ES ;cycles=3
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C336 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:08DD 57 PUSH DI ;cycles=3
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C334 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:08DE 56 PUSH SI ;cycles=3
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C332 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:08DF 53 PUSH BX ;cycles=3
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C330 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:08E0 52 PUSH DX ;cycles=3
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C32E EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:08E1 B81116 MOV AX,1611 ;cycles=3 (WIN386GETSHELL)
EAX=00001611 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C32E EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:08E4 33DB XOR BX,BX ;cycles=2
EAX=00001611 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C32E EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:08E6 CD2F INT 2F ;cycles=2
EAX=00001611 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C32E EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:08E8 0BC0 OR AX,AX ;cycles=133
EAX=00001611 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C32E EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000206 V0 D0 I1 T0 S0 Z0 A0 P1 C0
0E36:08EA B80000 MOV AX,0000 ;cycles=2
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C32E EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000206 V0 D0 I1 T0 S0 Z0 A0 P1 C0
0E36:08ED 7507 JNZ 08F6 ;cycles=2
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C32E EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000206 V0 D0 I1 T0 S0 Z0 A0 P1 C0
0E36:08F6 5A POP DX ;cycles=7
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C330 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000206 V0 D0 I1 T0 S0 Z0 A0 P1 C0
0E36:08F7 5B POP BX ;cycles=5
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C332 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000206 V0 D0 I1 T0 S0 Z0 A0 P1 C0
0E36:08F8 5E POP SI ;cycles=5
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C334 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000206 V0 D0 I1 T0 S0 Z0 A0 P1 C0
0E36:08F9 5F POP DI ;cycles=5
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C336 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000206 V0 D0 I1 T0 S0 Z0 A0 P1 C0
0E36:08FA 07 POP ES ;cycles=5
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C338 EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000206 V0 D0 I1 T0 S0 Z0 A0 P1 C0
0E36:08FB 1F POP DS ;cycles=5
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C33A EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000206 V0 D0 I1 T0 S0 Z0 A0 P1 C0
0E36:08FC C3 RET ;cycles=5
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C33C EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000206 V0 D0 I1 T0 S0 Z0 A0 P1 C0
0E36:214D 0BC0 OR AX,AX ;cycles=11
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C33C EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:214F 7415 JZ 2166 ;cycles=2
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C33C EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:2166 33C0 XOR AX,AX ;cycles=7
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C33C EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:2168 C3 RET ;cycles=2
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C33E EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:0E52 0BC0 OR AX,AX ;cycles=11
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C33E EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:0E54 7406 JZ 0E5C ;cycles=2
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C33E EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:0E5C E80B13 CALL 216A ;cycles=7
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C33C EBP=0000C444 ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:216A C8040000 ENTER 0004,00 ;cycles=7
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C336 EBP=0000C33A ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:216E 57 PUSH DI ;cycles=11
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C334 EBP=0000C33A ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:216F 56 PUSH SI ;cycles=3
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C332 EBP=0000C33A ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:2170 52 PUSH DX ;cycles=3
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C330 EBP=0000C33A ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:2171 50 PUSH AX ;cycles=3
EAX=00000000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C32E EBP=0000C33A ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:2172 B80030 MOV AX,3000 ;cycles=3
EAX=00003000 EBX=00000000 ECX=00000018 EDX=00000000
ESP=0000C32E EBP=0000C33A ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:2175 CD21 INT 21 ;cycles=2
EAX=00001E03 EBX=00000000 ECX=00000000 EDX=00000000
ESP=0000C32E EBP=0000C33A ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:2177 86E0 XCHG AH,AL ;cycles=551
EAX=0000031E EBX=00000000 ECX=00000000 EDX=00000000
ESP=0000C32E EBP=0000C33A ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:2179 A3F697 MOV [97F6],AX ;cycles=3
EAX=0000031E EBX=00000000 ECX=00000000 EDX=00000000
ESP=0000C32E EBP=0000C33A ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:217C 58 POP AX ;cycles=3
EAX=00000000 EBX=00000000 ECX=00000000 EDX=00000000
ESP=0000C330 EBP=0000C33A ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:217D 5A POP DX ;cycles=5
EAX=00000000 EBX=00000000 ECX=00000000 EDX=00000000
ESP=0000C332 EBP=0000C33A ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000246 V0 D0 I1 T0 S0 Z1 A0 P1 C0
0E36:217E 813EF697000A CMP [97F6],0A00 ;cycles=5
1A4F:97F6 031E 0000 0000 0001 1A4F 0000 0000 1A4F ........O.....O.
EAX=00000000 EBX=00000000 ECX=00000000 EDX=00000000
ESP=0000C332 EBP=0000C33A ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000287 V0 D0 I1 T0 S1 Z0 A0 P1 C1
0E36:2184 7210 JC 2196 ;cycles=7
EAX=00000000 EBX=00000000 ECX=00000000 EDX=00000000
ESP=0000C332 EBP=0000C33A ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000287 V0 D0 I1 T0 S1 Z0 A0 P1 C1
0E36:2196 813EF6971403 CMP [97F6],0314 ;cycles=7 (DOS 3.20 is the MINIMUM supported DOS version)
EAX=00000000 EBX=00000000 ECX=00000000 EDX=00000000
ESP=0000C332 EBP=0000C33A ESI=00004748 EDI=00004748
SS=1A4F DS=1A4F ES=0000 FS=0000 GS=0304 PS=00000206 V0 D0 I1 T0 S0 Z0 A0 P1 C0
0E36:219C 7308 JNC 21A6 ;cycles=7
So far, so good, since I was running PC-DOS 3.30. However, the next error message I received was:
Not enough free Extended/XMS memory to run Setup.
Setup needs approximately 2816000 bytes of free Extended/XMS memory.
I was running a machine with only 1Mb of extended memory. Time to install more memory and try again.
---
OK, that was easy. The next problem was triggered by the CAB ("Diamond") decompression code in Windows 95 Setup,
which uses all 32 bits of the 80386's 32-bit registers. That was not a problem, but by leaving stray bits in the
upper halves of registers like EDX, it exposed a bug in the PCjs I/O instruction handlers, which neglected to mask
EDX with 0xFFFF before performing port lookup, causing mysterious I/O failures that usually manifested themselves
as hard disk I/O errors.
More later.
*[@jeffpar](http://twitter.com/jeffpar)*
*July 14, 2015*
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