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4.6.4
SQ Protection
Determination of an exception in a write to an SQ or transfer to external memory (PREF
instruction) is performed as follows according to whether the MMU is on or off. If an exception
occurs in an SQ write, the SQ contents may be corrupted. If an exception occurs in transfer from
an SQ to external memory, the transfer to external memory will be aborted.
• When MMU is on
Operation is in accordance with the address translation information recorded in the UTLB, and
MMUCR.SQMD. Write type exception judgment is performed for writes to the SQs, and read
type for transfer from the SQs to external memory (PREF instruction), and a TLB miss
exception, protection violation exception, or initial page write exception is generated.
However, if SQ access is enabled, in privileged mode only, by MMUCR.SQMD, an address
error will be flagged in user mode even if address translation is successful.
• When MMU is off
Operation is in accordance with MMUCR.SQMD.
0: Privileged/user access possible
1: Privileged access possible
If the SQ area is accessed in user mode when MMUCR.SQMD is set to 1, an address error will
be flagged.
Rev. 4.0, 04/00, page 81 of 850
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