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PDP-11/20 test machine can load BASIC from paper tape, but still has some trouble running it

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This commit is contained in:
Jeff Parsons 2016-10-18 15:44:26 -07:00 • committed by Jeff Parsons
commit 16b8b59f12
14 changed files with 383 additions and 274 deletions
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61
modules/pdp11/lib/pc11.js
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@ -206,6 +206,8 @@ PC11.prototype.initBus = function(cmp, bus, cpu, dbg)
this.cpu = cpu;
this.dbg = dbg;
var pc11 = this;
this.configMount = this.cmp.getMachineParm('autoMount') || this.configMount;
if (this.configMount) {
@ -223,6 +225,12 @@ PC11.prototype.initBus = function(cmp, bus, cpu, dbg)
}
}
this.triggerReaderInterrupt = this.cpu.addTrigger(PDP11.PC11.RVEC, PDP11.PC11.PRI);
this.timerReaderAdvance = this.cpu.addTimer(function readyReader() {
pc11.advanceReader();
});
bus.addIOTable(this, PC11.UNIBUS_IOTABLE);
this.addTape("None", PC11.LOADSTATE.NONE, true);
@ -623,16 +631,57 @@ PC11.prototype.restore = function(data)
return true;
};
/**
* advanceReader()
*
* If the reader is enabled (RE is set) and there is no exceptional condition (ie, ERROR is set),
* and if the buffer register is empty (DONE is clear), then if we have more data in our internal buffer,
* store it in the buffer register, and optionally trigger an interrupt if device interrupts are enabled.
*
* @this {PC11}
*/
PC11.prototype.advanceReader = function()
{
if ((this.prs & (PDP11.PC11.PRS.RE | PDP11.PC11.PRS.ERROR)) == PDP11.PC11.PRS.RE) {
if (!(this.prs & PDP11.PC11.PRS.DONE)) {
if (this.iTapeData < this.aTapeData.length) {
this.prb = this.aTapeData[this.iTapeData++];
this.prs |= PDP11.PC11.PRS.DONE;
this.prs &= ~PDP11.PC11.PRS.BUSY;
if (this.prs & PDP11.PC11.PRS.RIE) {
this.cpu.setTrigger(this.triggerReaderInterrupt);
}
/*
* The PC11, by virtue of its "high speed", is supposed to deliver characters at 300 CPS,
* so for now, that's what we're going to deliver (ie, 1000ms / 300).
*
* TODO: Review this code. If we don't set the fReset parameter to true, the timer will eventually
* fire while the "Absolute Loader" tape is still reading bytes from, say, the "BASIC (Single User)"
* tape, causing an EXTRA advance to occur and causing a byte to be skipped. Passing true ensures
* that the timer cannot fire for AT LEAST 3ms after each advance. But again, I need to understand
* the reader's actual behavior.
*/
this.cpu.setTimer(this.timerReaderAdvance, 1000/300, true);
}
}
}
};
/**
* readPRS(addr)
*
* NOTE: We use the PRS RMASK to honor the "write-only" behavior of bit 0, the reader enable bit (RE), because
* DEC's tiny Bootstrap Loader (/apps/pdp11/boot/bootstrap/BOOTSTRAP-16KB.lst) repeatedly enables the reader using
* the INC instruction, which causes the PRS to be read, incremented, and written, so if bit 0 isn't always read
* as zero, the INC instruction would clear RE instead of setting it.
*
* @this {PC11}
* @param {number} addr (eg, PDP11.UNIBUS.PRS or 177550)
* @return {number}
*/
PC11.prototype.readPRS = function(addr)
{
return this.prs;
return this.prs & PDP11.PC11.PRS.RMASK; // RMASK honors the "write-only" nature of the RE bit by returning zero on reads
};
/**
@ -648,14 +697,16 @@ PC11.prototype.writePRS = function(data, addr)
if (this.prs & PDP11.PC11.PRS.ERROR) {
data &= ~PDP11.PC11.PRS.RE;
// if (this.prs & PDP11.PC11.PRS.RIE) {
// TODO: Generate an interrupt
// TODO: Generate an interrupt (error condition)
// }
} else {
this.prs &= ~PDP11.PC11.PRS.DONE;
this.prs |= PDP11.PC11.PRS.BUSY;
this.prb = 0;
}
}
this.prs = (this.prs & ~PDP11.PC11.PRS.WMASK) | (data & PDP11.PC11.PRS.WMASK);
this.advanceReader();
};
/**
@ -667,6 +718,12 @@ PC11.prototype.writePRS = function(data, addr)
*/
PC11.prototype.readPRB = function(addr)
{
/*
* I'm guessing that the DONE and BUSY bits always remain more-or-less inverses of each other. They definitely
* start out that way when writePRS() sets the reader enable (RE) bit, and so that's how we treat them elsewhere, too.
*/
this.prs &= ~PDP11.PC11.PRS.DONE;
this.prs |= PDP11.PC11.PRS.BUSY;
return this.prb;
};