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IDT MIPS32 4Kc Processor Core
Exceptions
79RC32438 User Reference Manual
2 - 40
November 4, 2002
Notes
Reset Exception
A reset exception occurs when the SI_ColdReset signal is asserted to the processor. This exception is
not maskable. When a Reset exception occurs, the processor performs a full reset initialization, including
aborting state machines, establishing critical state, and generally placing the processor in a state in which it
can execute instructions from uncached, unmapped address space. On a Reset exception, the state of the
processor in not defined, with the following exceptions:
The Random register is initialized to the number of TLB entries - 1 (4Kc core.
The Wired register is initialized to zero (4Kc core)
The Config register is initialized with its boot state
The RP, BEV, TS, SR, NMI, and ERL fields of the Status register are initialized to a specified state
The I, R, and W fields of the WatchLo register are initialized to 0
The ErrorEPC register is loaded with PC-4 if the state of the processor indicates that it was execut-
ing an instruction in the delay slot of a branch. Otherwise, the ErrorEPC register is loaded with PC.
Note that this value may or may not be predictable.
PC is loaded with 0xBFC0_0000.
Cause Register ExcCode Value:
None
Additional State Saved:
None
Entry Vector Used:
Reset (0xBFC0_0000)
Operation:
Random << TLBEntries - 1
Wired << 0
Config << ConfigurationState
StatusRP << 0
StatusBEV << 1
StatusTS << 0
StatusSR << 0
StatusNMI << 0
StatusERL << 1
WatchLoI << 0
WatchLoR << 0
WatchLoW << 0
if InstructionInBranchDelaySlot then
ErrorEPC << PC - 4
else
ErrorEPC << PC
endif
PC << 0xBFC0_0000
Soft Reset Exception
A soft reset exception occurs when the
SI_Reset
signal is asserted to the processor. This exception is
not maskable. When a soft reset exception occurs, the processor performs a subset of the full reset initial-
ization. Although a soft reset exception does not unnecessarily change the state of the processor, it may be
forced to do so in order to place the processor in a state in which it can execute instructions from uncached,
unmapped address space. Since bus, cache, or other operations may be interrupted, portions of the cache,
memory, or other processor state may be inconsistent. In addition to any hardware initialization required,
the following state is established on a soft reset exception:
The BEV, TS, SR, NMI, and ERL fields of the Status register are initialized to a specified state.