#Interrupt vector table emu8086 software
#Interrupt vector table emu8086 code

The vector table entry for timer interrupt is located at physical address 493 in page 0

Set IP to value stored in the interrupt vector table entry for the timer interrupt.

Mode, the address in SP is treated as a logical address and the machine performsДЄddress translation to calculate the physical address corresponding to the SP value.

Since the machine is executing in unpreviliged

*Increment the value of the SP register and push the value in the IP register into the memory address pointed to by SP.

At that point, the machine executes the following Of the XSM simulator), the tick counter is resetДЄnd a timer interrupt is raised. The number of ticks reaches a threshold specified during boot-time (see -timer option The timer ticks with each unprivileged instruction executed and once

The XSM architecture includes a timer that can cause periodic interrupts during execution Important Note: XSM does not allow the INT instruction to be executed in kernel mode. See here for more details about Boot ROM and interrupt vector table.

#Interrupt vector table emu8086 code

Since the values are hard-coded in the ROM code of the XSM simulator given to you, you cannot change the addresses of these handlers. When the machine encounters an INT n instruction, the corresponding ROM location is searched for the handler address and IP is set to this value.

#Interrupt vector table emu8086 software

Location 496 contains the address of the first software interrupt handler - INT 4, location 497 contains address of INT 5 handler and so on. Locations 492,493,494 and 495 stores the addresses of exception handler, timer interrupt handler, disk interrupt handler and console interrupt handler. The vector table is stored starting from physical address 492 of the ROM memory. Note: Internally XSM machine has an interrupt vector table that maps each interrupt number to a corresponding address (of the interrupt handler). It is the responsibility of the OS/Kernel programmer to store the interrupt handler routines in the disk and load them to the corresponding pages at the time of system startup. When an interrupt/exception occurs, the machine transfers control to the beginning of the first page of the corresponding handler. XSM specification reserves two contiguous memory pages for loading each interrupt handler according to the table given in Memory Organisation. When an interrupt occurs, the corresponding handler is executed.

However, hardware interrupts and the exception handler cannot be invoked from user mode programs.ДЄssociated with each interrupt/exception, there is an interrupt handler.

A program can invoke a software interrupt using the INT machine instruction. Software interrupts occur when they are invoked by a program in execution. The interrupts 4 to 18 are software interrupts. Interrupts 1, 2 and 3 are hardware interrupts. Among these, Interrupt 0 is the exception handler, Interrupt 1 is the timer interrupt, Interrupt 2 is the disk controller interrupt and Interrupt 3 is the console interrupt. Each interrupt is identified by its number between 0 and 18. User programs execute in the unpreviliged mode, the (incorrect) terminology has been used. However since the kernel of an OS normally runs in the previliged mode and Hence the above usage is incorrect technically. However, 'kernel' and 'user' are OS level abstractionsДЄnd not connected with the hardware. Important Note: Througout the architecture documentation, we have used the terms kernel mode for previleged modeДЄnd user mode for unprevileged mode of machine execution.