NEC Network Controller uPD98502 - Manual (Page 110)

CHAPTER 2 V R 4120A
110 Preliminary User’s Manual S15543EJ1V0UM
2.4.2.7 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 2-30. Table 2-29 lists the characteristics of the 32-bit Kernel mode segments, and Table 2-30 lists
the characteristics of the 64-bit Kernel mode segments.