506 Computer Architecture and Organization
E.10 EXCEPTION PROCESSING OF MIPS R4000
Every processor is designed to handle exceptional situations in some way or other and MIPS R4000 is
no exception. In general, these exceptions might be designated as an external interrupt, or some divide
by zero type errors. In the case of MIPS R4000, these exceptional situations may arise from
R TLB misses
R Arithmetic over ows
R I/O interrupts, and
R System calls
Whenever any such occasion is encountered by MIPS R4000, the processor disables all interrupts and
enters within its kernel mode of operation. It then executes a software exception handler located at a pre-
de ned address. The software is designed to save the entire operational status of the processor including
the program counter, the present operating mode along with the status of all interrupts. After servicing of
the exception, the original status of the processor may be restored through this saved information.
To process the exception, the processor loads the Exception Program Counter (EPC) with an address
from where the execution may restart after servicing the exception. Note that this EPC is different from
the normal program counter.
The exception processing takes the help of several registers earmarked for this purpose, having
information related to
R Context
R Bad address
R Count
R Compare register
R Status
R Cause
R EPC
R Memory reference Trap address Low
R Memory reference Trap address High
R XContext
R ECC
R Cache error and its status and
R Error of Exception Program Counter.
During exception handling, the general purpose registers of the processor are interlocked , but not the TLB.
MIPS processors offer several unique features as a pure RISC processor. The reader’s attention
is drawn to its surprisingly uniform and compact instruction format and set of instructions, which
forms the back bone of its classic architecture.
F
O
O
D
F
O
R
T
H
O
U
G
H
T
Z05_GHOS1557_01_SE_C20_App_E.indd 506Z05_GHOS1557_01_SE_C20_App_E.indd 506 4/29/11 5:46 PM4/29/11 5:46 PM
..................Content has been hidden....................
You can't read the all page of ebook, please click here login for view all page.