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Improved Print Throughput Via Multiple Index Command Task Scheduling

IP.com Disclosure Number: IPCOM000035739D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 4 page(s) / 35K

Publishing Venue

IBM

Related People

Damon, BW: AUTHOR [+3]

Abstract

Disclosed is an enhancement to a typical single task scheduling system for a bidirectional serial printer that results in improved throughput print speed without significantly increasing the size or complexity of the task scheduling program.

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Improved Print Throughput Via Multiple Index Command Task Scheduling

Disclosed is an enhancement to a typical single task scheduling system for a bidirectional serial printer that results in improved throughput print speed without significantly increasing the size or complexity of the task scheduling program.

In a typical low-cost bidirectional serial letter quality printer, the program used to control the scheduling of printer work items is relatively small and straightforward. In most cases, at most one level of task scheduling is permitted. For example, for the text shown in the figure, while the printer is actually printing line 1, the task scheduling system will usually allow datastream processing to be performed on the "CR,LF" index commands that must be done after line 1 printing is completed. To maintain an acceptable throughput speed, many systems allow the index work item to be scheduled for execution as a work "task"; then processing of the text for line 2 begins. This is necessary because the time required to prepare line 2 for printing is generally much longer than the time required to perform the index operation at the end of line 1. In a single task scheduling system, if line 2 is prepared for printing prior to the completion of the printing of line 1, then the datastream processing program must wait for the scheduled index to become active (since only one task can be scheduled for execution at a time). A system with multiple task scheduling capabilities is considerably larger and more complex and a single task scheduling system is normally adequate to maintain maximum throughput print speed for the level of printer being considered.

However, the occurrence of multiple forward motion commands (index) within text is relatively frequent (two line feeds at the end of paragraphs), and the limitation of being able to schedule ahead for only one work item may result in the printer temporarily stopping while the next line of text is prepared for printing. This occurs because the processing and execution of an index command is usually faster than the preparation of a line of text for printing. The line of text must be processed and ready for printing prior to completion of the execution of the active index command so that optimal overlapping of the index and print mechanisms can occur and so the optimal print direction for the next line may be determined in time to position the carrier for printing while the index is being performed. While there are usually several text patterns that cannot be printed at maximum throughput speed for most serial printers, the case of multiple index commands between lines of text occurs often enough in typical documents to justify making improvements for it. An example of this case may be seen in the figure. The text for line 7 must be completely processed and ready for printing before the line feed command from line 6 is complete. Otherwise, optimal overlapping of index and print cannot occu...