MIPS R10000 Microprocessor User's Manual - SGI TechPubs Library

238 Chapter 14.
14.2 Random Register (1)
The Random register is a read-only register of which six bits index an entry in the
TLB. This register decrements when any instruction graduates at that particular
cycle, and its values range between an upper and a lower bound, as follows:
• The lower bound is set by the number of TLB entries reserved for
exclusive use by the operating system (the contents of the Wired
register).
• The upper bound is set by the total number of TLB entries minus 1
(64 – 1 maximum).
The Random register specifies the entry in the TLB that is affected by the TLB Write
Random instruction. The register does not need to be read for this purpose;
however, the register is readable to verify proper operation of the processor.
To simplify testing, the Random register is set to the value of the upper bound upon
system reset. This register is also set to the upper bound when the Wired register
is written.
Figure 14-2 shows the format of the Random register; Table 14-3 describes the
Random register fields.
26 6
Figure 14-2 Random Register
Table 14-3 Random Register Field Descriptions
Field Description
Random TLB Random index
0
Random Register
31 6 5 0
Reserved. Must be written as zeroes, and returns zeroes
when read.
Version 2.0 of January 29, 1997 MIPS R10000 Microprocessor User's Manual
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Random