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Added the PDP-10's four arithmetic flags along with a negate() function -- the first of our functions that actually needs to set those flags

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Jeff 2017-03-01 17:23:54 -08:00 • committed by Jeff Parsons
commit 202374dd09
6 changed files with 417 additions and 283 deletions
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49
modules/pdp10/lib/cpustate.js
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@ -176,6 +176,7 @@ class CPUStatePDP10 extends CPUPDP10 {
{
this.regEA = this.regRA = this.regOP = 0;
this.regPC = this.lastPC = this.addrReset;
this.fOverflow = this.fCarry0 = this.fCarry1 = this.fNoDivide = false;
/*
* This is queried and displayed by the Panel when it's not displaying its own ADDRESS register
@ -327,25 +328,29 @@ class CPUStatePDP10 extends CPUPDP10 {
/**
* getOpcode()
*
* Normally, this fetches the next opcode in regOP, decodes the low 23 bits (I,X,Y), records the effective
* address (E) in regEA, updates regPC, and returns the high 13 bits of the opcode for further decoding.
* Normally, this fetches the next opcode in regOP, decodes the low 23 bits (I,X,Y), records
* the effective address (E) in regEA, updates regPC, and returns the high 13 bits of the opcode
* for further decoding.
*
* However, if a reference address still needs to be decoded (due to indirection), we take care of that first.
* However, if a reference address (R) in regRA still needs to be decoded (due to indirection),
* we take care of that first.
*
* @this {CPUStatePDP10}
* @return {number} (-1 if the reference address in regRA has not yet been fully decoded)
*/
getOpcode()
{
if ((this.regRA & PDP10.OPCODE.I_BIT)) {
this.regRA = this.readWord(this.regEA);
} else {
this.regRA = this.regOP = this.readWord(this.lastPC = this.regPC);
}
/*
* Technically, we don't REALLY need to mask regRA with R_MASK, because all regRA accesses
* ignore any higher opcode bits, but let's keep things tidy.
* ignore any higher bits, but let's keep things tidy.
*/
if ((this.regRA & PDP10.OPCODE.I_BIT)) {
this.regRA = this.readWord(this.regEA) & PDP10.OPCODE.R_MASK;
} else {
this.regRA = (this.regOP = this.readWord(this.lastPC = this.regPC)) & PDP10.OPCODE.R_MASK;
}
this.regRA &= PDP10.OPCODE.R_MASK;
/*
* Bits 0-22 (I,X,Y) contain what we call a "reference address" (R), which is used to calculate an
@ -433,6 +438,32 @@ class CPUStatePDP10 extends CPUPDP10 {
this.regPC = addr % PDP10.ADDR_LIMIT;
}
/**
* negate(src)
*
* @this {CPUStatePDP10}
* @param {number} src (36-bit)
* @return {number} (negated 36-bit src)
*/
negate(src)
{
if (!src) {
this.fCarry = this.fCarry1 = true;
}
else {
/*
* In the non-zero case, it's always safe to subtract src from TWO_POW36, but since we have to check for
* the MIN_NEG36 case anyway, and since subtraction in that case doesn't alter src, we skip the subtraction.
*/
if (src == PDP10.MIN_NEG36) {
this.fOverflow = this.fCarry1 = true;
} else {
src = PDP10.TWO_POW36 - src;
}
}
return src;
}
/**
* addIRQ(vector, priority, message)
*