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CHAPTER 4 MEMORY MANAGEMENT SYSTEM
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(c) xsuseg (64-bit Supervisor mode, user space)
When SX = 1 in the Status register and bits 63 and 62 of the virtual address space are set to 00, the
xsuseg virtual address space is selected; it covers 1 Tbyte (2
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 0000 0000 and runs through
0x0000 00FF FFFF FFFF.
40
bytes) of the current user address
(d) xsseg (64-bit Supervisor mode, current supervisor space)
When SX = 1 in the Status register and bits 63 and 62 of the virtual address space are set to 01, the
xsseg virtual address space is selected; it covers 1 Tbyte (2
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 0x4000 0000 0000 0000 and runs
through 0x4000 00FF FFFF FFFF.
40
bytes) of the current supervisor virtual
(e) csseg (64-bit Supervisor mode, separate supervisor space)
When SX = 1 in the Status register and bits 63 and 62 of the virtual address space are set to 11, the
csseg virtual address space is selected; it covers 512 Mbytes (2
virtual 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 0xFFFF FFFF C000 0000 and runs
through 0xFFFF FFFF DFFF FFFF.
29
bytes) of the separate supervisor
(3) Kernel-mode virtual addressing
If the Status register satisfies any of the following conditions, the processor runs in Kernel mode.
"
KSU = 00
"
EXL = 1
"
ERL = 1
The addressing width in Kernel mode varies according to the state of the KX bit of the Status register,
as follows:
"
When KX = 0, 32-bit kernel space is selected.
"
When KX = 1, 64-bit kernel space is selected.
The processor enters Kernel mode whenever an exception is detected and it remains in Kernel mode
until an exception return (ERET) instruction is executed and results in ERL and/or EXL = 0. The ERET
instruction restores the processor to the mode existing prior to the exception.
Kernel mode virtual address space is divided into regions differentiated by the high-order bits of the
virtual address, as shown in Figure 4-7. Table 4-3 lists the characteristics of the 32-bit Kernel mode
segments, and Table 4-4 lists the characteristics of the 64-bit Kernel mode segments.