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Fixed PC-DOS 7.00 CPU detection logic (see SGDT)

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This commit is contained in:
Jeff Parsons 2014-10-23 16:46:58 -07:00 • committed by jeffpar
commit 0173492ef2
12 changed files with 198 additions and 93 deletions
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51
my_modules/pcjs-client/lib/x86op0f.js
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@ -210,9 +210,44 @@ var X86Op0F = {
if (this.regEA < 0) {
X86Help.opInvalid.call(this);
} else {
this.setWord(this.regEA + 2, this.addrGDT);
this.setByte(this.regEA + 4, this.addrGDT >> 16);
/*
* We don't need to setWord() the first word of the operand, because the ModRM group decoder that calls
* us does that automatically with the value we return (dst).
*/
dst = this.addrGDTLimit - this.addrGDT;
this.setWord(this.regEA + 2, this.addrGDT);
/*
* We previously left the 6th byte of the target operand "undefined". But it turns out we have to set
* it to *something*, because there's processor detection in PC-DOS 7.0 (at least in the SETUP portion)
* that looks like this:
*
* 145E:4B84 9C PUSHF
* 145E:4B85 55 PUSH BP
* 145E:4B86 8BEC MOV BP,SP
* 145E:4B88 B80000 MOV AX,0000
* 145E:4B8B 50 PUSH AX
* 145E:4B8C 9D POPF
* 145E:4B8D 9C PUSHF
* 145E:4B8E 58 POP AX
* 145E:4B8F 2500F0 AND AX,F000
* 145E:4B92 3D00F0 CMP AX,F000
* 145E:4B95 7511 JNZ 4BA8
* 145E:4BA8 C8060000 ENTER 0006,00
* 145E:4BAC 0F0146FA SGDT [BP-06]
* 145E:4BB0 807EFFFF CMP [BP-01],FF
* 145E:4BB4 C9 LEAVE
* 145E:4BB5 BA8603 MOV DX,0386
* 145E:4BB8 7503 JNZ 4BBD
* 145E:4BBA BA8602 MOV DX,0286
* 145E:4BBD 89163004 MOV [0430],DX
* 145E:4BC1 5D POP BP
* 145E:4BC2 9D POPF
* 145E:4BC3 CB RETF
*
* This code is expecting SGDT on an 80286 to set the 6th "undefined" byte to 0xFF. So we use setWord()
* instead of setByte() and force the upper byte to 0xFF. TODO: Remove the 0xFF00 on post-80286 processors.
*/
this.setWord(this.regEA + 4, 0xFF00 | (this.addrGDT >> 16));
this.nStepCycles -= 11;
}
return dst;
@ -227,9 +262,17 @@ var X86Op0F = {
if (this.regEA < 0) {
X86Help.opInvalid.call(this);
} else {
this.setWord(this.regEA + 2, this.addrIDT);
this.setByte(this.regEA + 4, this.addrIDT >> 16);
/*
* We don't need to setWord() the first word of the operand, because the ModRM group decoder that calls
* us does that automatically with the value we return (dst).
*/
dst = this.addrIDTLimit - this.addrIDT;
this.setWord(this.regEA + 2, this.addrIDT);
/*
* As with SGDT, the 6th byte is technically "undefined" on an 80286, but given that SGDT now sets it to 0xFF,
* we mimic SGDT.
*/
this.setWord(this.regEA + 4, 0xFF00 | (this.addrIDT >> 16));
this.nStepCycles -= 12;
}
return dst;