NEC Network Controller uPD98502 - Manual (Page 162)

CHAPTER 2 V R 4120A
162 Preliminary User’s Manual S15543EJ1V0UM
Figure 2-62. TLB/XTLB Refill Exception Handling (2/2)
(b) Servicing TLB/XTLB Refill Exceptions (Software)
• 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
X/Context register
ERET
Servicing by each exception routine
• The execution of the ERET instruction is disabled in the
branch delay slots for other jump instructions.
• The processor does not execute an instruction in the branch
delay slot for the ERET instruction.
• PC ← EPC, EXL ← 0
• The physical address for a virtual address that is loaded into
the Context register is loaded into the EntryLo register and written
to the TLB.
• As long as a data/instruction address exists in the mapping
space, another TLB Refill exception may occur. In such
a case, EXL = 1 is set, causing a jump to the common
exception vector. (In this case, the common exception handler
handles the TLB miss, the ERET instruction returns control to
the user program, then a TLB Refill exception is generated
again.)