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TI486 Microprocessor - Al Kossow's Bitsavers

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Register Set<br />

During task switching, the processor saves the current CPU state in the TSS<br />

before starting a new task. The TR points to the current TSS. The TSS can be<br />

either a 286-type 16-bit TSS or a 386/486-type 32-bit TSS as shown in<br />

Figure 2-11 and Figure 2-12. An I/O permission bit map is referenced in the<br />

32-bit TSS by the I/O Map Base Address.<br />

Figure 2-11. 32-8it Task State Segment (TSS) Table<br />

31<br />

I/O MAP BASE ADDRESS<br />

0 0 0 0 0 0 0 0 0 0 0 o 0<br />

0 0 0 0 0 0 0 0 0 0 0 o 0<br />

0 0 0 0 0 0 0 0 0 0 0 o 0<br />

0 0 0 0 0 0 0 0 0 0 0 o 0<br />

0 0 0 0 0 0 0 0 0 0 0 o 0<br />

0 0 0 0 0 0 0 0 0 0 0 o 0<br />

0 0 0 0 0 0 0 0 0 0 0 o 0<br />

0 0 0 0 0 0 0 0 0 0 0 o 0<br />

0 0 0 0 0 0 0 0 0 0 0 o 0<br />

0 0 0 0 0 0 0 0 0 0 0 o 0<br />

0 0 0 0 0 0 0 0 0 0 0 o 0<br />

16 15<br />

o 0 000000000000<br />

0 0 0 SELECTOR FOR TASK'S LDT<br />

0 0 0 GS<br />

0 0 0 FS<br />

0 0 0 DS<br />

0 0 0 SS<br />

0 0 0 CS<br />

0 0 0 ES<br />

EDI<br />

ESI<br />

EBP<br />

ESP<br />

EBX<br />

EDX<br />

ECX<br />

EAX<br />

EFLAGS<br />

EIP<br />

CR3<br />

o 0 0 SS for CPL = 2<br />

ESP for CPL = 2<br />

000 SS for CPL = 1<br />

ESP for CPL = 1<br />

000 SS for CPL = 0<br />

ESP for CPL = 0<br />

000 BACK LINK (OLD TSS SELECTOR)<br />

o<br />

OIT +64h<br />

+60h<br />

+5Ch<br />

+58h<br />

+54h<br />

+50h<br />

+4Ch<br />

+48h<br />

+44h<br />

+40h<br />

+3Ch<br />

+38h<br />

+34h<br />

+30h<br />

+2Ch<br />

+28h<br />

+24h<br />

+20h<br />

+1Ch<br />

+18h<br />

+14h<br />

+10h<br />

+Ch<br />

+8h<br />

+4h<br />

+Oh<br />

0= RESERVED<br />

2-25

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