## Input/Output Device Driver Reference

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### Glossary - I

I

IDC - Inter-device-driver communication.

in-memory buffer - A block of memory in the address space of the host machine, used for data transfer.

init time - See initialization time, device driver.

initialization time, device driver - After the OS/2 loads a device driver, it sends it an OS/2 request packet to initialize. During this initialization, certain DevHlp functions are not permitted. Also called init time.

Input/Output Control (IOCtl) - A system service that provides a way for an application to send device-specific control commands to a device driver.

Input/Output Privilege Level (IOPL) - Allows part of a Ring 3 application or device driver to execute at Ring 0.

input router - OS/2 internal process that removes messages from the system queue.

inter-device-driver communication (IDC) - A mechanism that enables a physical device driver to communicate with another physical device driver.

interprocess communication - In the OS/2 operating system, the exchange of information between processes or threads through semaphores, queues, and shared memory.

interrupt - An instruction that directs the microprocessor to suspend what it is doing and run a specified routine. When the routine is complete, the microprocessor resumes its original work. See also routine.

interrupt request (IR) - Broadly, an "interrupt request level", referring to pending or in-service interrupt requests, or to a specific level (for example, IR 4).

interrupt request flag - A bit in the 8259 PIC controller that indicates an interrupt is pending on particular level. The VPIC also maintains a virtual interrupt request flag for each interrupt level for each DOS session.

interrupt service flag - A bit in the 8259 PIC controller that indicates an interrupt request is being serviced. It is cleared when the PIC is sent EOI . The VPIC maintains a virtual interrupt service flag indicating that a simulated interrupt is in-progress in a DOS session.

interrupt time - When a device driver is run because of an interrupt rather than because of an application request. OS/2 device drivers receive interrupts either from the hardware they manage or from the system real- time clock.

During interrupt time, certain DevHlp functions are not permitted. Also, addresses received directly from OS/2 applications might not be valid unless they are converted system addresses.

IOCtl - Input/Output Control.

IOPL - Input/Output Privilege Level.

IORB - Input/Output Request Block.

Input/Output Request Block (IORB) - A data structure defined by this specification that is passed as a parameter on all calls to an adapter device driver. It contains a fixed section, followed by a command-dependent section.

IORBH - Input/Output Request Block Header

IRET - Interrupt return.

IRQ - Interrupt Request.