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Fix pushing/popping at the limits of the stack segment

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This commit is contained in:
Jeff Parsons 2015-06-02 15:39:13 -07:00
commit badaaa307e
2 changed files with 6 additions and 7 deletions
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2
blog/2015/06/01/README.md
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@ -39,7 +39,7 @@ The Video component installs I/O port handlers for all possible I/O ranges; when
associated I/O operations are redirected to a dummy Card, so that the active Card isn't affected. Here,
however, that was insufficient. If the VGA is the only installed video card, the VGA ROM expects *NO RESPONSE*
on inactive CRTC ports. So I've changed the CRTC I/O handlers to check the Card's fActive flag. This seems
like a safe and logical change, but we'll still have to check for backward-compatibility issues with older ROMs.
like a safe and logical change, but I still have to check for backward-compatibility issues with older ROMs.
The VGA ROM programs the card for the first time here:

11
modules/pcjs/lib/x86cpu.js
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@ -3542,8 +3542,8 @@ X86CPU.prototype.popWord = function()
* There's no such thing as an SS fault on the 8086/8088, and I'm assuming that, on newer
* processors, when the stack segment limit is set to the maximum, it's OK for the stack to wrap.
*/
if (this.model <= X86.MODEL_8088 || this.segSS.limit == this.segSS.addrMask) {
this.setSP(this.regLSP - this.segSS.base);
if (this.model <= X86.MODEL_8088 || !this.segSS.fExpDown && this.segSS.limit == this.segSS.addrMask || this.segSS.fExpDown && !this.segSS.limit) {
this.setSP((this.regLSP - this.segSS.base) & this.segSS.addrMask);
} else if (off < -1) { // fudge factor
X86.fnFault.call(this, X86.EXCEPTION.SS_FAULT, 0);
}
@ -3570,11 +3570,10 @@ X86CPU.prototype.pushWord = function(w)
if (((this.regLSP - this.regLSPLimitLow)|0) < 0 && (this.regLSPLimitLow ^ this.regLSP) >= 0) {
/*
* There's no such thing as an SS fault on the 8086/8088, and I'm assuming that, on newer
* processors, when the stack segment is expand-down and the limit is set to the "maximum" of
* zero, it's OK for the stack to wrap.
* processors, when the stack segment limit is set to the maximum, it's OK for the stack to wrap.
*/
if (this.model <= X86.MODEL_8088 || this.segSS.fExpDown && !this.segSS.limit) {
this.setSP(this.regLSP - this.segSS.base);
if (this.model <= X86.MODEL_8088 || !this.segSS.fExpDown && this.segSS.limit == this.segSS.addrMask || this.segSS.fExpDown && !this.segSS.limit) {
this.setSP((this.regLSP - this.segSS.base) & this.segSS.addrMask);
} else {
X86.fnFault.call(this, X86.EXCEPTION.SS_FAULT, 0);
}