Mips Technologies R4000 - Processor Status Outputs

MIPS R4000 Microprocessor User's Manual 241
Clock Interface
10.6 Processor Status Outputs
The R4400 processor provides eight status outputs, Status(7:0), aligned
with each rising edge of MasterClock. At time T (the first PCycle of
MasterClock when status is examined) these status outputs indicate
whether the machine was running or stalled during the previous T-2 and
T-3 PCycles, as follows:
• If the machine was stalled during the T-2 or T-3 PCycles, the
status outputs indicate the type of stall which occurred (listed
in Table 10-1).
• If the machine was running during the T-2 or T-3 PCycles, the
status outputs describe the type of instruction which occupied
the WriteBack pipeline stage during the T-2 or T-3 PCycles, and
which was successfully completed (listed in Table 10-1).
• The status outputs also indicate if an instruction in the T-2 or
T-3 PCycle was killed, and if so, states the cause (listed in
Table 10-1.
The Status(7:0) bits are treated as two fields, as follows:
• The Status(7:4) field indicates the internal status of the
processor during PCycle T-3.
• The Status(3:0) bits indicate the internal status of the processor
during the PCycle T-2.