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Immunized cursor blink rate from changes to CPU speed

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This commit is contained in:
Jeff Parsons 2016-08-23 12:52:11 -07:00
commit c1b34a87ed
5 changed files with 219 additions and 201 deletions
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15
modules/pc8080/lib/keyboard.js
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@ -893,12 +893,12 @@ Keyboard8080.prototype.checkSoftKeysToRelease = function()
* options:
*
* 1) Snapshot the CPU cycle count each time a byte is transmitted (see outVT100UARTStatus()) and then every
* time this is polled, see if the cycle count has exceeded the snapshot value by the necessary threshold
* amount; if we assume 361.69ns per CPU cycle, there are 22 CPU cycles for every 1 LBA4 cycle, and since
* transmission time is supposed to last for 160 LBA4 cycles, that means 22*160 CPU cycles, or 3520 cycles.
* time this is polled, see if the cycle count has exceeded the snapshot value by the necessary threshold;
* if we assume 361.69ns per CPU cycle, there are 22 CPU cycles for every 1 LBA4 cycle, and since transmission
* time is supposed to last for 160 LBA4 cycles, the threshold is 22*160 CPU cycles, or 3520 cycles.
*
* 2) Set a CPU timer using the new setTimer() interface, which can be passed the number of milliseconds to
* wait before firing (in this case, 7945ms).
* wait before firing (in this case, roughly 1.27ms).
*
* 3) Call the ChipSet's getVT100LBA(4) function for the state of the simulated LBA4, and count 160 LBA4
* transitions; however, that would be the worst solution, because there's no guarantee that the firmware's
@ -912,7 +912,12 @@ Keyboard8080.prototype.checkSoftKeysToRelease = function()
Keyboard8080.prototype.isVT100TransmitterReady = function()
{
if (this.fVT100UARTBusy) {
if (this.cpu.getCycles() >= this.nVT100UARTCycleSnap + 3520) {
/*
* NOTE: getCyclesMS(1.2731488) should work out to 3520 cycles for a CPU clocked at 361.69ns per cycle,
* which is roughly 2.76Mhz. We could just hard-code 3520 instead of calling getCyclesMS(), but this helps
* maintain a reasonable blink rate for the cursor even when the user cranks up the CPU speed.
*/
if (this.cpu.getCycles() >= this.nVT100UARTCycleSnap + this.cpu.getCyclesMS(1.2731488)) {
this.fVT100UARTBusy = false;
}
}