16.3 Virtual Address Translation
Address Space Identification (ASID)
Each independent task, or process, has a separate address space, assigned a unique 8-bit Address Space Identifier (ASID). This identifier is stored with each TLB entry to distinguish between entries loaded for different processes. The ASID allows the processor to move from one process to another (called a context switch) without having to invalidate TLB entries.
The processor's current ASID is stored in the low 8 bits of the EntryHi register. These bits are also used to load the ASID field of an entry during TLB refill.
The ASID field of each TLB entry is compared to the EntryHi register; if the ASIDs are equal or if the entry is global (see below), this TLB entry may be used to translate virtual addresses. The ASID comparison is performed only when a new value is loaded into the EntryHi register; the one-bit result of the match is stored in a static Enable latch. (This bit is set whenever a new entry is loaded.)
Copyright 1995, MIPS Technologies, Inc. -- 29 JAN 96
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