iAPX 286 Operating System Writers Guide 1983

iAPX286 MACRO ASSEMBLER Enter Protected Mod. 960-516 date ?AG=systeM-IO iAPX286 MACqO ASSEMBLER Vx.y ASSEMBLY CF MODULE ENTP05JtCT MUOULE PLACED IN :Fl:ENTP~C3JASSEMBLER INVOKED 3Y: ASM286.86 :cl:E~TP.A86lLOC09JLINESOURCE...o~'" IOT_OESC,GOT_OESC,STARTSwitch the 90286 from real address mode into protected ~ode.Th. initial EPR~M GOT, lOT, T5S, and LOT Cif any) constructed by BL0286are copied from EPRO~ into RA~. The RAM areaS are defined by dataseg~ents allocated as fixod entri.s i~ tho ~DT. The CPU registers forthe GOT, lOT, TSS, and LOT or • • et to pOlnt at the RAM basedsegments. The base fields in the RAM GOT are also updated topoint at the RA~ based segments.Interrupts are disabled during this mod. switching code.The EPROM bas.d GOT, leT, TSS, and LOT are checked to assurethey are valid before copying them to RAM. If any of the RAM-~asQdalias s09ments are smaller than the EPROM s~~~ents they are to hold,h~lt or shutdown occurs. In general any exception or NMI caUSeS5hutdown to occur until the first task is invoked.If the RAM segment is larger than the EPROM seg~ent. the RAM segmentis expanded with zeroes. If the initial TS5 specifies an LOT,the LOT is also copied into LDT_ALIAS with Zero fill if needed.Tne EPROM or qA~ based GOT, IDT, TS5, and LOT segments may be locatedanywhere in physical memory_Define layout of a descriptor.STRUCOWOWDBDB011ENDSooOffset of last byte in segmentLow 16 bits of 14-bit addressHigh 8 bits of 24-bit addressAccess rights byteReserved wordDefine the fixed GOT selector values for the descriptors thatdefine the EPROM based tablas.Figure 10-1. Initialization Module ENTPen-