Basic I/O handling on burroughs B6500

摘要

The approach to processing basic Input/Output in B6500 hardware design and software implementation is discussed in this paper. Hardware I/O structure necessary to the understanding of the approach is described first. The representation of the I/O queue and the algorithms used in handling I/O requests are described in detail to emphasize the ease with which the I/O handling portions of the executive system may be modified to suit any installation. Some of the I/O tables for coordinating I/O activity are discussed. The concept of asynchronous processes running as extended arms of the executive system is discussed and the implementation of it for updating status of peripheral units, for handling I/O errors, etc. is described. The usage and implementation of I/O related events and software interrupts is discussed. The locking concept is presented. Finally, the complete I/O initiation and completion cycle is described. The description throughout this paper is based on the actual working system implemented with language ESPOL - an extended ALGOL language used for writing executive systems. Some of the special language constructs pertinent to I/O handling are illustrated.