{File name: Protected.mc

Last Edited: Amy Fasnacht November 16, 1981 2:22 PM: Change register names
Last Edited: Jozef Furst November 4, 1981 3:18 PM: multiple allocation corrected (Carry changed to RefCarry)
Last Edited: Amy Fasnacht October 23, 1981 11:40 AM: Change register names to prevent conflict with SAx00Initial.mc names
Last Edited: Amy Fasnacht September 11, 1981 9:52 AM: make clock update atomic
Last Edited: Jim Frandeen August 19, 1981 4:30 PM: add clock update to refresh task.
Description: Protected microcode for Initial,
Author: Jarvis,
Created: December 5, 1980,
}

Set[OverlayStart, Add[ProtectFence, 1]];

Reserve[OverlayStart, 0FFF];
{
Phase0Protected (Protected.mc, IOPBoot.mc) resides in 0 - 00FF
Phase0 (Phase0.mc, DiskBootDLion.mc, EtherBootDLion.mc) resides in 0100 - 0FDF
The BootKernel resides in 0FE0 - 0FFF
Part of the BootKernel that can be overlaid resides in 0FD8 - 0FDF
}

SetTask[0];

{clobber only rC before going to external fault handler}

Trap:rC← RRot1 ErrnIBnStkp, ClrIntErr, CANCELBR[$, 0F],c1, at[0];
[]← passTraps, ZeroBr,c2;
BRANCH[$, Trap1],c3;
GOTOABS[ErrorHandlerLoc],c1; {pass the trap on}
Trap1:acR← bootTrap, GOTO[catchAll2],c1;

catchAll1:Noop,c1, at[Maintenance1Loc];
catchAll2:Noop,c2, at[Maintenance2Loc];
catchAll3:rB← 0, rBrh← 0,c3, at[Maintenance3Loc];
MAR← [rBrh, rB+1],c1;
MDR← acR and 0FF, CANCELBR[$, 0],c2;
IOPCtl← IOPInMode,c3; {enable IOP}
infinite:GOTO[infinite],c*, at[IdleLoc];

SetTask[1]; StartAddress[Refresh];

{We come here once per line, or every 28.8 usec.
That means 34,722 times per second}
Refresh:rJ ← rJ - 1 {Decrement clock low}, ZeroBr, Refresh, CANCELBR[$, 0F],c1;
BRANCH[NoCarry, RefCarry],c2;

RefCarry:rG ← rG - 1 {Decrement clock high}, GOTO[TestTimeout],c3;
NoCarry:
Noop,c3;
TestTimeout:
Ybus ← rJ or rG, ZeroBr, Refresh,c1;
rN ← 1, BRANCH[$, Timeout],c2;
ClrDPRq, GOTO[Refresh],c3;

Timeout:uTimeout ← rN, ClrDPRq, GOTO[Refresh],c3;