PIT.js

function PIT(PC,set_irq_callback,cycle_count_callback){var s,i;this.pit_channels=new Array();for(i=0;i<3;i++){s=new IRQCH(cycle_count_callback);this.pit_channels[i]=s;s.mode=3;s.gate=(i!=2)>>0;s.pit_load_count(0);}
this.speaker_data_on=0;this.set_irq=set_irq_callback;PC.register_ioport_write(0x40,4,1,this.ioport_write.bind(this));PC.register_ioport_read(0x40,3,1,this.ioport_read.bind(this));PC.register_ioport_read(0x61,1,1,this.speaker_ioport_read.bind(this));PC.register_ioport_write(0x61,1,1,this.speaker_ioport_write.bind(this));}
function IRQCH(cycle_count_callback){this.count=0;this.latched_count=0;this.rw_state=0;this.mode=0;this.bcd=0;this.gate=0;this.count_load_time=0;this.get_ticks=cycle_count_callback;this.pit_time_unit=1193182/2000000;}
IRQCH.prototype.get_time=function(){return Math.floor(this.get_ticks()*this.pit_time_unit);};IRQCH.prototype.pit_get_count=function(){var d,dh;d=this.get_time()-this.count_load_time;switch(this.mode){case 0:case 1:case 4:case 5:dh=(this.count-d)&0xffff;break;default:dh=this.count-(d%this.count);break;}
return dh;};IRQCH.prototype.pit_get_out=function(){var d,eh;d=this.get_time()-this.count_load_time;switch(this.mode){default:case 0:eh=(d>=this.count)>>0;break;case 1:eh=(d<this.count)>>0;break;case 2:if((d%this.count)==0&&d!=0)
eh=1;else
eh=0;break;case 3:eh=((d%this.count)<(this.count>>1))>>0;break;case 4:case 5:eh=(d==this.count)>>0;break;}
return eh;};IRQCH.prototype.get_next_transition_time=function(){var d,fh,base,gh;d=this.get_time()-this.count_load_time;switch(this.mode){default:case 0:case 1:if(d<this.count)
fh=this.count;else
return-1;break;case 2:base=(d/this.count)*this.count;if((d-base)==0&&d!=0)
fh=base+this.count;else
fh=base+this.count+1;break;case 3:base=(d/this.count)*this.count;gh=((this.count+1)>>1);if((d-base)<gh)
fh=base+gh;else
fh=base+this.count;break;case 4:case 5:if(d<this.count)
fh=this.count;else if(d==this.count)
fh=this.count+1;else
return-1;break;}
fh=this.count_load_time+fh;return fh;};IRQCH.prototype.pit_load_count=function(x){if(x==0)
x=0x10000;this.count_load_time=this.get_time();this.count=x;};PIT.prototype.ioport_write=function(mem8_loc,x){var hh,ih,s;mem8_loc&=3;if(mem8_loc==3){hh=x>>6;if(hh==3)
return;s=this.pit_channels[hh];ih=(x>>4)&3;switch(ih){case 0:s.latched_count=s.pit_get_count();s.rw_state=4;break;default:s.mode=(x>>1)&7;s.bcd=x&1;s.rw_state=ih-1+0;break;}}else{s=this.pit_channels[mem8_loc];switch(s.rw_state){case 0:s.pit_load_count(x);break;case 1:s.pit_load_count(x<<8);break;case 2:case 3:if(s.rw_state&1){s.pit_load_count((s.latched_count&0xff)|(x<<8));}else{s.latched_count=x;}
s.rw_state^=1;break;}}};PIT.prototype.ioport_read=function(mem8_loc){var Pg,ma,s;mem8_loc&=3;s=this.pit_channels[mem8_loc];switch(s.rw_state){case 0:case 1:case 2:case 3:ma=s.pit_get_count();if(s.rw_state&1)
Pg=(ma>>8)&0xff;else
Pg=ma&0xff;if(s.rw_state&2)
s.rw_state^=1;break;default:case 4:case 5:if(s.rw_state&1)
Pg=s.latched_count>>8;else
Pg=s.latched_count&0xff;s.rw_state^=1;break;}
return Pg;};PIT.prototype.speaker_ioport_write=function(mem8_loc,x){this.speaker_data_on=(x>>1)&1;this.pit_channels[2].gate=x&1;};PIT.prototype.speaker_ioport_read=function(mem8_loc){var eh,s,x;s=this.pit_channels[2];eh=s.pit_get_out();x=(this.speaker_data_on<<1)|s.gate|(eh<<5);return x;};PIT.prototype.update_irq=function(){this.set_irq(1);this.set_irq(0);};