Fujitsu FR81S 用户手册
CHAPTER 3: CPU
10. Memory Protection Function (MPU)
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CHAPTER : CPU
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10.4.4.
Data Access Errors
This section explains data access errors of the CPU.
If the following conditions are satisfied during a data access, this is treated as a data access error and the
access information at that time are stored in the data access error address register (DEAR) and data access
error status register (DESR). However, if data access error information already exists in the above register
(DESR.DAE =1), this is not overwritten.
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System register access in user mode
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Bus error during data access
The operation after a bus error occurs during data access differs between accesses with buffering enabled
and accesses with buffering disabled. System register accesses in user mode are always processed as illegal
instruction exceptions (data access).
If a data access error occurs during access to an unbufferable area, the CPU processes this as an illegal
instruction exception (data access error).
If a data access error occurs during access to a bufferable area, and if the data access error interrupt is
enabled by MPU control register MPUCR.DEE =1, the data access error interrupt is triggered and the CPU
performs data access error interrupt processing. If a data access error occurs during access to a bufferable
area, because the CPU is executing a subsequence instruction, the PC saved when the data access error
interrupt occurs is not the PC value for the instruction that performed the data access.
If an illegal instruction exception (data access error) occurs during the execution of an instruction that
performs multiple data accesses, the data accesses that had executed up until the error occurred are not
cancelled. If an illegal instruction exception (data access error) occurs during the LDM0, LDM1, STM0,
STM1, FLDM, or FSTM instructions, the list of remaining registers is stored in the exception status register
ESR.RL, and the bit indicating a data access error ESR.INV6 is set.
If an illegal instruction exception (data access error) occurs during the EIT processing sequence or the RETI
instruction, the CPU is halted and can only be recovered by break interrupt or reset.
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