Intel 8253 - Page 318

AP-578
20
2/21/97 12:57 PM 24329102.DOC
INTEL CONFIDENTIAL
(until publication date)
; RESTORE MODIFIED STATE IMAGE
MOV BYTE PTR [EBP-104], 0H
FRSTOR [EBP-108]
; DE-ALLOCATE STACK SPACE, RESTORE REGISTERS
MOV ESP, EBP
.
.
POP EBP
;
; RETURN TO INTERRUPTED CALCULATION
IRETD
SAVE_ALL ENDP
Example 2. Reduced-Latency Exception Handler
SAVE_ENVIRONMENT PROC
;
; SAVE REGISTERS, ALLOCATE STACK SPACE FOR FPU ENVIRONMENT
PUSH EBP
.
.
MOV EBP, ESP
SUB ESP, 28 ; ALLOCATES 28 BYTES (32-bit PROTECTED MODE SIZE)
;SAVE ENVIRONMENT, RESTORE INTERRUPT ENABLE FLAG (IF)
FNSTENV [EBP-28]
PUSH [EBP + OFFSET_TO_EFLAGS] ; COPY OLD EFLAGS TO STACK TOP
POPFD ; RESTORE IF TO VALUE BEFORE FPU EXCEPTION
;
; APPLICATION-DEPENDENT EXCEPTION HANDLING CODE GOES HERE
;
; CLEAR EXCEPTION FLAGS IN STATUS WORD (WHICH IS IN MEMORY)
; RESTORE MODIFIED ENVIRONMENT IMAGE
MOV BYTE PTR [EBP-24], 0H
FLDENV [EBP-28]
; DE-ALLOCATE STACK SPACE, RESTORE REGISTERS
MOV ESP, EBP
.
.
POP EBP
;
; RETURN TO INTERRUPTED CALCULATION
IRETD
SAVE_ENVIRONMENT ENDP
Example 3. Reentrant Exception Handler
LOCAL_CONTROL DW ? ; ASSUME INITIALIZED
.
.
REENTRANT PROC
;
; SAVE REGISTERS, ALLOCATE STACK SPACE FOR FPU STATE IMAGE