Nec Network Controller uPD98502 Manual do Utilizador Página 160

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CHAPTER 2 V
R
4120A
160
Preliminary User’s Manual S15543EJ1V0UM
Figure 2-61. Common Exception Handling (2/2)
(b) Servicing Common Exceptions (Software)
The processor is reset.
(In Kernel mode, interrupts are enabled.)
After EXL = 0 is set, all exceptions are enabled (although the
Interrupt exception can be masked by the IE and IM bits, and the
Cache Error exception can be masked by the DE bit.)
The occurrence of TLB Refill, TLB Invalid, and TLB Modified
exceptions is disabled by using an unmapped space.
The occurrence of the Watch and Interrupt exceptions is
disabled by setting EXL = 1.
Other exceptions are avoided in the OS programs.
However, the Cold Reset, Soft Reset, and NMI exceptions are
enabled.
Execute MFC0 instruction
(Status bit setting)
KSU bit
00
EXL bit
0
IE bit
1
Execute MFC0 instruction
X/Context register
EPC register
Status register
Cause register
ERET
Servicing by each exception routine
Check the Cause register, and jump
to each routine
TS bit = 0?
Yes
No
The register files are saved.
EXL = 1
Execute MTC0 instruction
EPC register
Status register
The execution of the ERET instruction is disabled in the
delay slots for the other jump instructions.
The processor does not execute an instruction in the branch
delay slot for the ERET instruction.
PC
EPC, EXL
0
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