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User’s Manual
IBM PowerPC 750GX and GL RISC Microprocessor
gx_04.fm.(1.2)
March 27, 2006
Exceptions
Page 163 of 377
The setting of the exception prefix bit (IP) determines how exceptions are vectored. If the bit is cleared,
exceptions are vectored to the physical address 0x000n_nnnn (where nnnnn is the vector offset). If IP is set,
exceptions are vectored to physical address 0xFFFn_nnnn. Table 4-2 on page 152 shows the exception
vector offset of the first instruction of the exception handler routine for each exception type.
4.5.1 System Reset Exception (0x00100)
The 750GX implements the system reset exception as defined in the PowerPC Architecture (OEA). The
system reset exception is a nonmaskable, asynchronous exception signaled to the processor through the
assertion of system-defined signals. In the 750GX, the exception is signaled by the assertion of either the soft
reset (SRESET
) or hard reset (HRESET) inputs, described more fully in Chapter 7, Signal Descriptions, on
page 249
The 750GX implements HID0[NHR], which helps software distinguish a hard reset from a soft reset. Because
this bit is cleared by a hard reset, but not by a soft reset, software can set this bit after a hard reset and tell
whether a subsequent reset is a hard or soft reset by examining whether this bit is still set.
The first bus operation following the negation of HRESET
or the assertion of SRESET will be a single-beat
instruction fetch (caching will be inhibited) to x00100.
Table 4-6 lists register settings when a system reset exception is taken.
System management 0 — 0 0 0 — 0 0 0 0 — 0 0 0 0 ILE
Performance monitor 0 — 0 0 0 — 0 0 0 0 — 0 0 0 0 ILE
Thermal management 0 — 0 0 0 — 0 0 0 0 — 0 0 0 0 ILE
Table 4-6. System Reset Exception–Register Settings
Register Setting Description
SRR0
Set to the effective address of the instruction that the processor would have attempted to execute next if no exception
conditions were present.
SRR1
0 Loaded with equivalent MSR bits
1:4 Cleared
5:9 Loaded with equivalent MSR bits
10:15 Cleared
16:31 Loaded with equivalent MSR bits
Note: If the processor state is corrupted to the extent that execution cannot resume reliably, MSR[RI] (SRR1[30]) is
cleared.
MSR
POW 0
ILE —
EE 0
PR 0
FP 0
ME —
FE0 0
SE 0
BE 0
FE1 0
IP —
IR 0
DR 0
PM 0
RI 0
LE Set to value of ILE
Table 4-5. MSR Setting Due to Exception (Page 2 of 2)
Exception Type
MSR Bit
2
POW ILE EE PR FP ME FE0 SE BE FE1 IP IR DR PM RI LE
Note:
1. A zero indicates that the bit is cleared.
2. The ILE bit is copied from the MSR[ILE].
3. A dash indicates that the bit is not altered.
4. Reserved bits are read as if written as 0.