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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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21
modules/pdp11/lib/cpuops.js
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@ -52,7 +52,7 @@ if (NODE) {
*
* For example, opADD() passes the helper function fnADD() to the appropriate update method. This
* allows the update method to perform the entire read/modify/write operation, because the modify
* step is performed internally via the fnXXX() helper function.
* step is performed internally, via the fnXXX() helper function.
*/
/**
@ -1117,7 +1117,24 @@ PDP11.opHALT = function(opCode)
this.regErr |= PDP11.CPUERR.BADHALT;
this.trap(PDP11.TRAP.BUS_ERROR, PDP11.REASON.HALT);
} else {
this.stopCPU();
if (!this.dbg) {
/*
* This will leave the PC exactly where it's supposed to be: at the address of the HALT + 2.
*/
this.stopCPU();
} else {
/*
* When the Debugger is present, this call will rewind PC by 2 so that the HALT instruction is
* displayed, making it clear why the processor stopped; the user could also use the "dh" command
* to dump the Debugger's instruction history buffer to see why it stopped, assuming the history
* buffer is enabled, but that's more work.
*
* Because rewinding is not normal CPU behavior, attempting to Run again (or use the Debugger's
* "g" command) will cause an immediate HALT again; the work-around is simple: either set the PC to
* a new address (eg, "r pc=pc+2") or single-step the HALT instruction ("t").
*/
this.dbg.stopInstruction();
}
}
this.nStepCycles -= 7;
};