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
