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AMD Geode™ LX Processors Data Book 89
5
CPU Core 33234H
5.0CPU Core
This section describes the internal operations of the
AMD Geode™ LX processor’s CPU Core from a program-
mer’s point of view. It includes a description of the tradi-
tional “core” processing and FPU operations. The
integrated function registers are described in the next
chapter.
The primary register sets within the processor core include:
• Application Register Set
• System Register Set
5.1 Core Processor Initialization
The CPU Core is initialized when the RESET# (Reset) sig-
nal is asserted. The CPU Core is placed in real mode and
the registers listed in Table 5-1 are set to their initialized
values. RESET# invalidates and disables the CPU cache,
and turns off paging. When RESET# is asserted, the CPU
terminates all local bus activity and all internal execution.
While RESET# is asserted, the internal pipeline is flushed
and no instruction execution or bus activity occurs.
Approximately 150 to 250 external clock cycles after
RESET# is de-asserted, the processor begins executing
instructions at the top of physical memory (address location
FFFFFFF0h). The actual number of clock cycles depends
on the clock scaling in use. Also, before execution begins,
an additional 2
20
clock cycles are needed when self-test is
requested.
Typically, an intersegment jump is placed at FFFFFFF0h.
This instruction forces the processor to begin execution in
the lowest 1 MB of address space. Table 5-1 lists the CPU
Core registers and illustrates how they are initialized.
Table 5-1. Initialized Core Register Controls
Register Register Name
Initialized Contents
(Note 1) Comments
EAX Accumulator xxxxxxxxh 00000000h indicates self-test passed.
EBX Base xxxxxxxxh
ECX Count xxxxxxxxh
EDX Data xxxx 04 [DIR0]h DIR0 = Device ID
EBP Base Pointer xxxxxxxxh
ESI Source Index xxxxxxxxh
EDI Destination Index xxxxxxxxh
ESP Stack Pointer xxxxxxxxh
EFLAGS Extended Flags 00000002h See Table 5-4 on page 93 for bit definitions.
EIP Instruction Pointer 0000FFF0h
ES Extra Segment 0000h Base address set to 00000000h. Limit set to FFFFh.
CS Code Segment F000h Base address set to FFFF0000h. Limit set to FFFFh.
SS Stack Segment 0000h Base address set to 00000000h. Limit set to FFFFh.
DS Data Segment 0000h Base address set to 00000000h. Limit set to FFFFh.
FS Extra Segment 0000h Base address set to 00000000h. Limit set to FFFFh.
GS Extra Segment 0000h Base address set to 00000000h. Limit set to FFFFh.
IDTR Interrupt Descriptor Table Register Base = 0, Limit = 3FFh
GDTR Global Descriptor Table Register xxxxxxxxh
LDTR Local Descriptor Table Register xxxxh
TR Task Register xxxxh
CR0 Control Register 0 60000010h See Table 5-10 on page 96 for bit descriptions.
CR2 Control Register 2 xxxxxxxxh See Table 5-9 on page 96 for bit descriptions.
CR3 Control Register 3 xxxxxxxxh See Table 5-8 on page 96 for bit descriptions.
CR4 Control Register 4 00000000h See Table 5-7 on page 96 for bit descriptions.
Note 1. x = Undefined value.