|
| Interrups | Categories | Contents |
AH = 89h BL = interrupt number of IRQ0 (IRQ1-7 use next 7 interrupts) BH = interrupt number of IRQ8 (IRQ9-F use next 7 interrupts) ES:SI -> GDT for protected mode (see #00500)
Return:
CF set on error AH = FFh error enabling address line 20 CF clear if successful AH = 00h in protected mode at specified address BP may be destroyed; all segment registers change
Notes: BL and BH must be multiples of 8. The protected-mode CS must reference the same memory as the CS this function is called from because execution continues with the address following the interrupt call
See Also: AH=87h - AH=88h - INT 67/AX=DE0Ch
Format of BIOS switch-to-protected-mode Global Descriptor Table: Offset Size Description (Table 00500) 00h 8 BYTEs null descriptor (initialize to zeros) 08h 8 BYTEs GDT descriptor (see #00501) 10h 8 BYTEs IDT descriptor 18h 8 BYTEs DS descriptor 20h 8 BYTEs ES 28h 8 BYTEs SS 30h 8 BYTEs CS 38h 8 BYTEs uninitialized, used to build descriptor for BIOS CS
Format of segment descriptor table entry: Offset Size Description (Table 00501) 00h WORD segment limit, low word 02h 3 BYTEs segment base address, low 24 bits 05h BYTE access mode (see #00502) 06h BYTE 386+ extended access mode (see #00505) 07h BYTE 386+ segment base address, high 8 bits
See Also: #00500 - INT 2C/AX=0002h - INT 31/AX=0009h
Bitfields for segment descriptor table access mode field: Bit(s) Description (Table 00502) 3-0 segment type (see #00503,#00504) 4 descriptor type (1 = application, 0 = system) 6-5 descriptor privilege level 7 segment is present in RAM
See Also: #00501 - #00505
(Table 00503) Values for system segment descriptor type: 0 reserved 1 available 16-bit TSS 2 LDT 3 busy 16-bit TSS 4 16-bit call gate 5 task gate 6 16-bit interrupt gate 7 16-bit trap gate 8 reserved 9 available 32-bit TSS 10 reserved 11 busy 32-bit TSS 12 32-bit call gate 13 reserved 14 32-bit interrupt gate 15 32-bit trap gate
See Also: #00502 - #00504
Bitfields for application segment descriptor type: Bit(s) Description (Table 00504) 3 code/data. 0 date. 1 code ---data segments--- 2 expand down 1 writeable ---code segments--- 2 conforming 1 readable ------ 0 accessed
See Also: #00502 - #00503
Bitfields for 386+ segment descriptor table extended access mode field: Bit(s) Description (Table 00505) 3-0 high 4 bits of segment limit 4 available 5 reserved (0) 6 default operation size (1 = 32 bits, 0 = 16 bits) 7 granularity (1 = 4K, 0 = byte)
See Also: #00501 - #00502 - #02557
|
| Interrups | Categories | Contents |