
5-14
G2 PowerPC Core Reference Manual
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MOTOROLA
Exception Processing
The IEEE floating-point exception mode bits (FE0 and FE1) together define whether
floating-point exceptions are handled precisely, imprecisely, or if they are taken at all. The
possible settings and default conditions for the G2 core are shown in Table 5-8. For further
details, see Chapter 6, “Exceptions,” in the
Programming Environments Manual
.
MSR bits are guaranteed to be written to SRR1 when the first instruction of the exception
handler is encountered.
5.2.2
Enabling and Disabling Exceptions
When a condition exists that may cause an exception to be generated, it must be determined
whether the exception is enabled for that condition as follows:
IEEE floating-point enabled exceptions (a type of program exception) are ignored
when both MSR[FE0] and MSR[FE1] are cleared. If either of these bits are set, all
IEEE enabled floating-point exceptions are taken and cause a program exception.
26
IR
Instruction address translation
0 Instruction address translation is disabled
1 Instruction address translation is enabled
See
Chapter 6, “Memory Management.”
27
DR
Data address translation
0 Data address translation is disabled
1 Data address translation is enabled
See
Chapter 6, “Memory Management.”
28–29
—
Reserved. Full function.
30
RI
Recoverable exception (for system reset and machine check exceptions)
0 Exception is not recoverable
1 Exception is recoverable
31
LE
Little-endian mode enable
0 The processor runs in big-endian mode
1 The processor runs in little-endian mode. For the G2_LE core, see Section 1.1.2.1, “True
Little-Endian Mode,” for a definition of whether the core is operating in true little-endian
mode or modified little-endian mode.
Table 5-8. IEEE Floating-Point Exception Mode Bits
FE0
FE1
Mode
0
0
Floating-point exceptions disabled
0
1
Floating-point imprecise nonrecoverable
1
1
Not implemented in the G2 core.
1
0
Floating-point imprecise recoverable
1
1
1
Floating-point precise mode
Table 5-7. MSR Bit Settings (continued)
Bits
Name
Description
F
Freescale Semiconductor, Inc.
n
.