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MPC8240 Integrated Processor User’s Manual
Exception Model
5.5 Exception Model
This section describes the PowerPC exception model and implementation-specific details
of the MPC8240 core.
5.5.1 PowerPC Exception Model
The PowerPC exception mechanism allows the processor to change to supervisor state as a
result of external signals, errors, or unusual conditions arising in the execution of
instructions. When exceptions occur, information about the state of the processor is saved
to certain registers and the processor begins execution at an address (exception vector)
predetermined for each exception. Processing of exceptions occurs in supervisor mode.
Although multiple exception conditions can map to a single exception vector, a more
specific condition may be determined by examining a register associated with the
exception. For example, the DSISR identifies instructions that cause a DSI exception.
Additionally, some exception conditions can be explicitly enabled or disabled by software.
The PowerPC architecture requires that exceptions be handled in program order; therefore,
although a particular implementation may recognize exception conditions out of order,
exceptions are taken in strict order. When an instruction-caused exception is recognized,
any unexecuted instructions that appear earlier in the instruction stream, including any that
have not yet entered the execute stage, are required to complete before the exception is
taken. Any exceptions caused by those instructions are handled first. Likewise, exceptions
that are asynchronous and precise are recognized when they occur, but are not handled until
the instruction currently in the completion stage successfully completes execution or
generates an exception, and the completed store queue is emptied.
Unless a catastrophic condition causes a system reset or machine check exception, only one
exception is handled at a time. If, for example, a single instruction encounters multiple
exception conditions, those conditions are handled sequentially. After the exception handler
handles an exception, the instruction execution continues until the next exception condition
Write-with-flush
Write-with-flush-atomic
Non-locked PCI write to memory or
locked PCI write to memory,
respectively
• If the addressed block is in the exclusive
state, the snoop forces the state of the
addressed block to invalid.
• If the addressed block is in the modified
state, the snoop causes a push of the modified
block out of the cache to memory and changes
the state of the block to invalid.
Write-with-kill
Locked or non-locked PCI write with
invalidate to memory
In a write-with-kill operation, the processor
snoops the cache for a copy of the addressed
block. If one is found the cache block is forced
to the I state, killing modified data that may
have been in the block.
Table 5-6. Transactions Reflected to the Processor for Snooping (Continued)
Snooped Transaction
Condition Detected by CCU
Processor Response
Summary of Contents for MPC8240
Page 1: ...MPC8240UM D Rev 1 1 2001 MPC8240 Integrated Processor User s Manual ...
Page 38: ...xviii MPC8240 Integrated Processor User s Manual TABLES Table Number Title Page Number ...
Page 48: ...xlviii MPC8240 Integrated Processor User s Manual Acronyms and Abbreviations ...
Page 312: ...6 94 MPC8240 Integrated Processor User s Manual ROM Flash Interface Operation ...
Page 348: ...7 36 MPC8240 Integrated Processor User s Manual PCI Host and Agent Modes ...
Page 372: ...8 24 MPC8240 Integrated Processor User s Manual DMA Register Descriptions ...
Page 394: ...9 22 MPC8240 Integrated Processor User s Manual I2O Interface ...
Page 412: ...10 18 MPC8240 Integrated Processor User s Manual Programming Guidelines ...
Page 454: ...12 14 MPC8240 Integrated Processor User s Manual Internal Arbitration ...
Page 466: ...13 12 MPC8240 Integrated Processor User s Manual Exception Latencies ...
Page 516: ...16 14 Watchpoint Trigger Applications ...
Page 538: ...B 16 MPC8240 Integrated Processor User s Manual Setting the Endian Mode of Operation ...
Page 546: ...C 8 MPC8240 Integrated Processor User s Manual ...
Page 640: ...INDEX Index 16 MPC8240 Integrated Processor User s Manual ...