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User's Manual
IBM PowerPC 750GX and GL RISC Microprocessor
System reset and machine-check exceptions can occur at any time and are not delayed even if an exception
is being handled. As a result, state information for an interrupted exception might be lost. Therefore, these
exceptions are typically nonrecoverable. An exception might not be taken immediately when it is recognized.
4.3 Exception Processing
When an exception is taken, the processor uses Machine Status Save/Restore Register 0 (SRR0) to deter-
mine where instruction processing should resume, and uses Machine Status Save/Restore Register 1
(SRR1) to save the contents of the Machine State Register (MSR) for the current context.
4.3.1 Machine Status Save/Restore Register 0 (SRR0)
When an exception occurs, the address saved in SRR0 determines where instruction processing should
resume when the exception handler returns control to the interrupted process. Depending on the exception,
this might be the address in SRR0 or the next address in the program flow. All instructions in the program flow
preceding this one will have completed execution, and no subsequent instruction will have begun execution.
This might be the address of the instruction that caused the exception or the next one (as in the case of a
system call, trace, or trap exception).
SRR0
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
Exceptions
gx_04.fm.(1.2)
Page 156 of 377
March 27, 2006
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