Coprocessor Interface
ARM DDI 0210C Copyright © 2001, 2004 ARM Limited. All rights reserved. 4-17
4.8 Privileged instructions
The output signal nTRANS enables the implementation of coprocessors, or
coprocessor instructions, that can only be accessed from privileged modes. The signal
meanings are given in Table 4-4.
If used, the nTRANS signal must be sampled at the same time as the coprocessor
instruction is fetched and is used in the coprocessor pipeline Decode stage.
Note
If a User mode process, with nTRANS LOW, tries to access a coprocessor instruction
that can only be executed in a privileged mode, the coprocessor responds with CPA and
CPB HIGH. This causes the ARM7TDMI processor to take the undefined instruction
trap.
Table 4-4 Mode identifier signal meanings, nTRANS
nTRANS Meaning
0 User mode instruction
1 Privileged mode instruction
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