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9-22 Vol. 3
PROCESSOR MANAGEMENT AND INITIALIZATION
9.10.1 Assembler Usage
In this example, the Intel assembler ASM386 and build tools BLD386 are used to
assemble and build the initialization code module. The following assumptions are
used when using the Intel ASM386 and BLD386 tools.
• The ASM386 will generate the right operand size opcodes according to the code-
segment attribute. The attribute is assigned either by the ASM386 invocation
controls or in the code-segment definition.
• If a code segment that is going to run in real-address mode is defined, it must be
set to a USE 16 attribute. If a 32-bit operand is used in an instruction in this code
segment (for example, MOV EAX, EBX), the assembler automatically generates
an operand prefix for the instruction that forces the processor to execute a 32-bit
operation, even though its default code-segment attribute is 16-bit.
• Intel's ASM386 assembler allows specific use of the 16- or 32-bit instructions, for
example, LGDTW, LGDTD, IRETD. If the generic instruction LGDT is used, the
default- segment attribute will be used to generate the right opcode.
188 195 Perform specific board initialization that is imposed by the new
protected mode
196 218 Copy the application's GDT from ROM into RAM
220 238 Copy the application's IDT from ROM into RAM
241 243 Load application's GDTR
244 245 Load application's IDTR
247 261 Copy the application's TSS from ROM into RAM
263 267 Update TSS descriptor and other aliases in GDT (GDT alias or IDT
alias)
277 277 Load the task register (without task switch) using LTR instruction
282 286 Load SS, ESP with the value found in the application's TSS
287 287 Push EFLAGS value found in the application's TSS
288 288 Push CS value found in the application's TSS
289 289 Push EIP value found in the application's TSS
290 293 Load DS, ES with the value found in the application's TSS
296 296 Perform IRET; pop the above values and enter the application code
Table 9-4. Main Initialization Steps in STARTUP.ASM Source Listing (Contd.)
STARTUP.ASM Line
Numbers
Description
From To