I

Inter-device-driver communication.

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

See 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.

A system service that provides a way for an application to send device-specific control commands to a device driver.

Allows part of a Ring 3 application or device driver to execute at Ring 0.

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

A mechanism that enables a physical device driver to communicate with another physical device driver.

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

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.

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

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.

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.

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.

Input/Output Control.

Input/Output Privilege Level.

Input/Output Request Block.

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.

Input/Output Request Block Header

Interrupt return.

Interrupt Request.