Mips Technologies R4000 - Random Register (1)

Chapter 4
86 MIPS R4000 Microprocessor User's Manual
Random Register (1)
The Random register is a read-only register of which six bits index an entry
in the TLB. This register decrements as each instruction executes, and its
values range between an upper and a lower bound, as follows:
• A lower bound is set by the number of TLB entries reserved for
exclusive use by the operating system (the contents of the
Wired register).
• An upper bound is set by the total number of TLB entries (47
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 4-12 shows the format of the Random register; Table 4-8 describes
the Random register fields.
Figure 4-12 Random Register
Table 4-8 Random Register Field Descriptions
Field Description
Random TLB Random index
0
Reserved. Must be written as zeroes, and returns zeroes
when read.
Random Register
31 6 5 0
26 6
Random
0