16.2 Virtual Address Space

Supervisor Mode Operations


Supervisor mode is designed for layered operating systems in which a true kernel runs in processor Kernel mode, and the rest of the operating system runs in Supervisor mode.

The processor operates in Supervisor mode when the Status register contains the Supervisor-mode bit-values shown in Table 16-1.

Figure 16-2 shows Supervisor mode address mapping.



Figure 16-2 Supervisor Mode Address Space

32-bit Supervisor Mode, User Space (suseg)

In Supervisor mode, when SX = 0 in the Status register and the most-significant bit of the 32-bit virtual address is set to 0, the suseg virtual address space is selected; it covers the full 231 bytes (2 Gbytes) of the current user address space. The virtual address is extended with the contents of the 8-bit ASID field to form a unique virtual address.

This mapped space starts at virtual address 0x0000 0000 and runs through 0x7FFF FFFF.

32-bit Supervisor Mode, Supervisor Space (sseg)

In Supervisor mode, when SX = 0 in the Status register and the three most-significant bits of the 32-bit virtual address are 1102, the sseg virtual address space is selected; it covers 229-bytes (512 Mbytes) of the current supervisor address space. The virtual address is extended with the contents of the 8-bit ASID field to form a unique virtual address.

This mapped space begins at virtual address 0xC000 0000 and runs through 0xDFFF FFFF.

64-bit Supervisor Mode, User Space (xsuseg)

In Supervisor mode, when SX = 1 in the Status register and bits 63:62 of the virtual address are set to 002, selection of the xsuseg virtual address space is dependent upon the UX bit.

The virtual address is extended with the contents of the 8-bit ASID field to form a unique virtual address.

64-bit Supervisor Mode, Current Supervisor Space (xsseg)

In Supervisor mode, when SX = 1 in the Status register and bits 63:62 of the virtual address are set to 012, the xsseg current supervisor virtual address space is selected. The virtual address is extended with the contents of the 8-bit ASID field to form a unique virtual address.

This mapped space begins at virtual address 0x4000 0000 0000 0000 and runs through 0x4000 0FFF FFFF FFFF.

64-bit Supervisor Mode, Separate Supervisor Space (csseg)

In Supervisor mode, when SX = 1 in the Status register and bits 63:62 of the virtual address are set to 112, the csseg separate supervisor virtual address space is selected. Addressing of the csseg is compatible with addressing sseg in 32-bit mode. The virtual address is extended with the contents of the 8-bit ASID field to form a unique virtual address.

This mapped space begins at virtual address 0xFFFF FFFF C000 0000 and runs through 0xFFFF FFFF DFFF FFFF.




Copyright 1995, MIPS Technologies, Inc. -- 29 JAN 96


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