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CHAPTER 5 EXCEPTION PROCESSING
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(a) Interrupt enable
Interrupts are enabled when all of the following conditions are true:
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IE is set to 1.
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EXL is cleared to 0.
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ERL is cleared to 0.
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The appropriate bit of the IM is set to 1.
(b) Operating modes
The following Status register bit settings are required for User, Kernel, and Supervisor modes.
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The processor is in User mode when KSU = 10, EXL = 0, and ERL = 0.
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The processor is in Supervisor mode when KSU = 01, EXL = 0, and ERL = 0.
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The processor is in Kernel mode when KSU = 00, EXL = 1, or ERL = 1.
(c) 32- and 64-bit modes
The following Status register bit settings select 32- or 64-bit operation for User, Kernel, and Supervisor
operating modes. Enabling 64-bit operation permits the execution of 64-bit opcodes and translation of
64-bit addresses. 64-bit operation for User, Kernel and Supervisor modes can be set independently.
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64-bit addressing for Kernel mode is enabled when KX bit = 1. 64-bit operations are always valid in
Kernel mode.
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64-bit addressing and operations are enabled for Supervisor mode when SX bit = 1.
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64-bit addressing and operations are enabled for User mode when UX bit = 1.
(d) Kernel address space accesses
Access to the kernel address space is allowed when the processor is in Kernel mode.
(e) Supervisor address space accesses
Access to the supervisor address space is allowed when the processor is in Supervisor or Kernel mode.
(f) User address space accesses
Access to the user address space is allowed in any of the three operating modes.
(2) Status register reset
The contents of the Status register are undefined after a Cold Reset, except for the following bits in the
Diagnostic Status field:
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TS = 0, SR = 0
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ERL and BEV = 1
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The SR bit distinguishes between a Cold Reset and Soft Reset.
Remark
Cold Reset and Soft Reset are the sequences to initialize the V
R
4100 CPU core. For details
about initialization of the whole V
R
4101 including on-chip peripheral units, refer to Chapter 7.