14.10 Status Register (12)
Diagnostic Status Field
The 9-bit Diagnostic Status (DS) field is used for self-testing, and checks the cache and virtual memory system. This field is described in Table 14-11 and shown Figure 14-12.
Some of the important DS fields include:
- In the R4400, the TS bit of the diagnostic field indicates a TLB shutdown has occurred due to matching of multiple virtual page entries during address translation. In the R10000 processor, the TS bit indicates a TLB write has introduced an entry that would allow matching of more than one virtual page entry during translation. In this case, the TLB entries that allow the multiple matches, even in the Wired area, are invalidated before the new TLB entry is written. This prevents multiple matches during address translation.
The TS bit is updated for each TLB write. It can also be read and written by software (in the R4400, the TS bit is read-only); to clear the TS bit one needs to write a 0 into it. As in the R4400, Reset/Soft Reset/NMI exceptions also clear the TS bit.
- The NMI bit is new to the R10000 processor; it distinguishes between Soft Reset and NMI exceptions. Both exceptions set the SR bit to 1; the NMI exception sets the NMI bit to 1, whereas the Soft Reset exception sets it to 0.
- The CE bit is reserved in the R10000 processor and should be a 0.
Figure 14-12 Diagnostic Status Field
Table 14-11 Status Register Diagnostic Status Bits
Copyright 1996, 1997, MIPS Technologies, Inc. -- 09 DEC 96
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