Programmable System and Power-On Resets (01-Jan-1987)

Programmable System and Power-On Resets

This article describes a technique used in the input/output (I/O) subsystem of a data processing system that allows the program in the processor to invoke resets equivalent to system and power-on resets for unattended environments. When an operating system is required to dynamically (versus manual intervention) change its operational character, it will first execute a program system reset. This will cause all target facilities to be set to the sane state that would normally result from an operator pressing the system reset button on a console. However, the command does not cause the target facilities to be reset completely. If the target (I/O) device is program initializable, and has been successfully initialized, then this initialization is not reset. Therefore the program does not completely lose a logical connection to the target subsequent to a program system reset. This obviates the necessity to have to reinitialize the targets of the program system reset. I/O device attachments have become increasingly more capable of initialization by means of program loadable parameters, microcode, and code visible to applications. It is not desirable to reset such initialization under normal circumstances, such as system resets, I/O halts, or device resets. However, it does not obviate the desirability of being able to reset initialization states of the attachment to the equivalent state induced by a power-on reset. The program pow...