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First change for v1.17.6: DeskPro 386-compatible A20 management

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This commit is contained in:
Jeff Parsons 2015-04-19 18:19:10 -07:00 • committed by jeffpar
commit f2cb4dc18d
127 changed files with 993 additions and 1003 deletions
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52
modules/pcjs/lib/x86cpu.js
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@ -186,11 +186,6 @@ function X86CPU(parmsCPU)
* so that if/when we call restore(), it will have something to fill in.
*/
this.resetRegs();
/*
* Initially, the logical A20 state should be true, but from this point on, it's up to the machine to decide.
*/
this.fA20 = true;
}
Component.subclass(X86CPU, CPU);
@ -642,42 +637,10 @@ X86CPU.prototype.initMemory = function(aMemBlocks, blockShift, blockLimit, block
}
};
/**
* setA20(fEnable)
*
* setA20() used to ONLY be a Bus function, but we now route all setA20() calls through the CPU,
* so that the CPU can maintain a logical A20 state (fA20), separate from the physical A20 state.
*
* In real-mode, all cpu.setA20() calls go straight to bus.setA20(), and we update the logical
* A20 state (fA20); in protected-mode, we only update the logical A20 state (fA20).
*
* In addition, when transitioning from real-mode to protected-mode, we call bus.setA20(true), and
* when transitioning back to real-mode, we call bus.setA20(fA20). See setProtMode() for details.
*
* This gives the CPU an unusual amount of control over the A20 line, but it protects us from "bad"
* protected-mode code that fails to ensure A20 is enabled; I've run into code in the Compaq DeskPro
* 386 ROM BIOS that fails without this work-around. This seems like a fairly safe hack, because
* it's hard to imagine any real-world protected-mode code relying on A20 being off. However, that
* doesn't change the fact that this hack should NOT be necessary.
*
* TODO: Figure out why the DeskPro 386 ROM BIOS misbehaves under emulation, and eliminate this hack.
*
* @this {X86CPU}
* @param {boolean} fEnable is true to enable A20, false to disable
*/
X86CPU.prototype.setA20 = function(fEnable)
{
this.fA20 = fEnable;
if (!(this.regCR0 & X86.CR0.MSW.PE)) {
this.bus.setA20(fEnable);
}
};
/**
* setAddressMask(busMask)
*
* Notification from Bus.setA20(), called whenever the physical A20 line changes; this is
* independent of the CPU's own logical A20 state (fA20).
* Notification from Bus.setA20(), called whenever the physical A20 line changes
*
* @this {X86CPU}
* @param {number} busMask
@ -1441,16 +1404,6 @@ X86CPU.prototype.setProtMode = function(fProt)
this.segFS.updateMode(fProt);
this.segGS.updateMode(fProt);
}
/*
* Work-around to update the A20 line whenever transitioning modes; see cpu.setA20() for details.
*
* Unfortunately, we can't immediately update the physical A20 line on return to real-mode, because
* segment registers are likely still loaded with base addresses above 1Mb, so we leave the physical
* A20 line enabled for now.
*
* if (this.bus) this.bus.setA20(fProt? true : this.fA20);
*/
if (this.bus && fProt) this.bus.setA20(true);
};
/**
@ -1464,7 +1417,7 @@ X86CPU.prototype.setProtMode = function(fProt)
X86CPU.prototype.saveProtMode = function()
{
if (this.addrGDT != null) {
return [this.regCR0, this.addrGDT, this.addrGDTLimit, this.addrIDT, this.addrIDTLimit, this.segLDT.save(), this.segTSS.save(), this.nIOPL, this.fA20];
return [this.regCR0, this.addrGDT, this.addrGDTLimit, this.addrIDT, this.addrIDTLimit, this.segLDT.save(), this.segTSS.save(), this.nIOPL];
}
return null;
};
@ -1488,7 +1441,6 @@ X86CPU.prototype.restoreProtMode = function(a)
this.segLDT.restore(a[5]);
this.segTSS.restore(a[6]);
this.nIOPL = a[7];
this.fA20 = (a[8] !== undefined? a[8] : this.bus.getA20());
this.setProtMode();
}
};