A trap is an exception in a user process. It's caused by division by zero or invalid memory access. It's also the usual way to invoke a kernel routine a system call because those run with a higher priority than user code. Handling is synchronous so the user code is suspended and continues afterwards. In a sense they are "active" - most of the time, the code expects the trap to happen and relies on this fact. These are asynchronous i.
You can also see a trap as a kind of CPU-internal interrupt since the handler for trap handler looks like an interrupt handler registers and stack pointers are saved, there is a context switch, execution can resume in some cases where it left off. A gate call, interrupt, task or trap is used to transfer control of execution across segments.
Privilege level checking is done differently depending on the type of destination and instruction used. Call gates transfer control from lower privilege code to higher privilege code.
The gate DPL is used to determine what privilege levels have access to the gate. Task gates are used for hardware multitasking support. It works the same way with interrupt or trap gates. Task gates are not used, to the best of my knowledge, as kernels usually want extra work done when task switching.
Main Menu Data Comm. Interrupt is an electronic alerting signal sent to the processor from an external device, either a part of the computer itself such as a disk controller or an external peripheral. Software Interrupt caused either by an exceptional condition e. An interrupt transfers control to an interrupt handler inside the operating system; it changes the operating system mode to kernel mode.
The main purpose of the interrupt is to bring attention to the CPU to some high priority events that have to be executed immediately. The trap is the same as the interrupt, its purpose is to bring attention to the CPU to execute system calls that are required in the execution of the user code.
You can understand the difference as Interrupt being the topic of the books and Trap is a small chapter in that book. An interrupt is a vast topic which has interrupt handlers, masked interrupts, unmasked interrupts, traps, exceptions, faults, etc. The Trap is a part of Interrupt but specifically deals with system calls for user code execution.
In my research, for the article, I have found in many websites which make the difference between the trap and interrupt look like the difference between the hardware and the software interrupt and which is very misleading. Interrupts are the signals that are emitted by the software or the hardware when any process or an event needs immediate attention. These signals are generated from the hardware and the software and therefore they are called the hardware and the software interrupts. These signals, when generated by the hardware or the software have to be attended by the operating system.
The operating system has some processes that are operating and these processes are present in the queue, so when the operating system receives the interrupt signals all the processes in the queue that were running are made to halt and CPU is made to attend to the signal of the interrupt. The reason why these interruptions are so useful to the operating system is that it is a way the hardware and software can communicate to the operating system.
If you move your mouse on the screen an interrupt is getting generated, if you press any key on a keyboard an interrupt is getting generated, if you print a document an interrupt is getting generated, if you power off the monitor screen an interrupt is getting generated, there are many such occasion such that operating system is waiting for some interrupts to take place and for attending the interrupts.
You can also conclude here that interrupts are a higher priority process which requires the interruption of the current working process. The method by which the CPU handles the interrupt is that the CPU checks after every instruction cycle time taken for completion of one instruction in the program whether or not an interrupt is pending to take action.
If the CPU does not find any interrupts to be pending then it will continue the execution of the next instruction of the program but if the CPU finds an interrupt pending then it will stop the execution of the instruction of the program and service the pending interrupt by calling the interrupt handler program. When the CPU finds the interrupt, the program will be put to the suspended mode to stop the program temporarily and the state of the program and the current instruction number will be saved by the CPU to attend it later on.
After this CPU will attend the interrupt and it will what interrupt is produced and what is the interrupt number and with this interrupt number it will match to a table interrupt vector table to know exactly which interrupt handler program will be needed to solve the interrupt and will give the necessary service to the interrupt generated.
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