Sun Microelectronics
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14. Implementation Dependencies
multiple nested traps, promoting processor efficiency while dramatically reduc-
ing the system overhead needed for trap handling. Three sets of alternate globals
are selected for different kinds of traps:
• MMU globals for memory faults
• Interrupt globals, and
• Alternate globals for all other exceptions.
This further increases OS performance, providing fast trap execution by avoiding
the need to save and restore registers while processing exceptions.
Figure 14-1 Nested Trap Levels
All traps supported in UltraSPARC are listed in Table 8-6, “Traps Supported in
UltraSPARC,” on page 158.
14.1.5 SIGM Support (Impdep #116)
UltraSPARC initiates a Software-Initiated Reset (SIR) by executing a SIGM in-
struction while in privileged mode. When in non-privileged mode, SIGM behaves
as a NOP. See also Section 10.1.3, “Software-Initiated Reset (SIR),” on page 171.
14.1.6 44-bit Virtual Address Space
UltraSPARC supports a 44-bit subset of the full 64-bit virtual address space. Al-
though the full 64 bits are generated and stored in integer registers, legal address-
es are restricted to two equal halves at the extreme lower and upper portions of
the full virtual address space. Virtual addresses between 0000 08FF FFFF FFFF
16
Level 0: Normal Program Execution
Level 1: System Calls, Interrupt Handlers, Emulation
Level 2: Exceptions in Common OS Routines
Level 3: Page Fault Handlers
Level 4: RED_state Handler
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