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VT100 SET-UP screen is accessible now

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This commit is contained in:
Jeff Parsons 2016-08-14 10:52:24 -07:00
commit e7324a5c6a
10 changed files with 5989 additions and 5856 deletions
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32
modules/pc8080/lib/chipset.js
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@ -169,13 +169,29 @@ ChipSet.SI1978 = {
/*
* One of the many chips in the VT100 is an 8224, which operates at 24.8832MHz. That frequency is divided by 9
* to yield a 361.69ns clock period for the 8080 CPU, which means the CPU is running at 2.76Mhz (cycles per second).
* Hence the CPU component in the VT100's machine.xml is defined as:
* to yield a 361.69ns clock period for the 8080 CPU, which means (in theory) that the CPU is running at 2.76Mhz.
*
* Hence the CPU component in the VT100's machine.xml SHOULD be defined as:
*
* <cpu id="cpu8080" model="8080" cycles="2764800"/>
*
* where 2764800 = 24883200 / 9. You need to know this because we rely on the CPU frequency for simulating some
* of the other VT100 circuits.
* where 2764800 = 24883200 / 9. Unfortunately, the VT100 ROM decrements a countdown value in memory to determine
* cursor blink rate, and if we use 2764800 cycles per second, the cursor blinks MUCH too fast. It's surprising that
* the VT100 doesn't rely on vertical retrace interrupts for blink rate. Perhaps the designers were concerned about
* consistency across 60Hz and 50Hz display modes, although that seems like a minor concern, considering that the
* alternative means the ROM is now tied to a specific CPU operating frequency. However, short of rewriting portions
* of the ROM, we have to deal with it.
*
* And we deal with it by lowering cycles per second to 1000000 (1Mhz). I'm guessing that in a real VT100, the 8080
* gets bogged down by other factors (eg, the Video Processor's DMA requests), but we don't simulate the hardware to
* that level of detail, so the easiest solution is to lower the effective clock speed.
*
* NOTE: If you've noticed that the VT100 cursor blinks unevenly, you're right, and it's by design: the ROM uses a
* countdown value for the cursor's "on" state that is twice as large as that for the cursor's "off" state, so it's
* "on" twice as long as it's "off".
*
* WARNING: The choice of clock speed has an effect on other simulated VT100 circuits; see the DC011 Timing Chip
* discussion below, along with the getVT100LBA() function.
*
* For reference, here is a list of all the VT100 I/O ports, from /devices/pc8080/machine/vt100/debugger/README.md,
* which in turn comes from p. 4-17 of the VT100 Technical Manual (July 1982):
@ -729,7 +745,7 @@ ChipSet.prototype.outSIWatchdog = function(port, b, addrFrom)
};
/**
* getVT100LBA(nBit)
* getVT100LBA(iBit)
*
* Returns the state of the requested (simulated) LBA bit.
*
@ -738,12 +754,12 @@ ChipSet.prototype.outSIWatchdog = function(port, b, addrFrom)
* period than if we divided the cycle count by 88, but a shorter LBA7 period is probably helpful in terms of
* overall performance.
*
* @param {number} nBit
* @param {number} iBit
* @return {number}
*/
ChipSet.prototype.getVT100LBA = function(nBit)
ChipSet.prototype.getVT100LBA = function(iBit)
{
return (this.cpu.getCycles() & (1 << (nBit - 1))) << 1;
return (this.cpu.getCycles() & (1 << (iBit - 1))) << 1;
};
/**