Browse Prior Art Database

Checkpointing for Printer Restart

IP.com Disclosure Number: IPCOM000052959D
Original Publication Date: 1981-Aug-01
Included in the Prior Art Database: 2005-Feb-12
Document File: 3 page(s) / 47K

Publishing Venue

IBM

Related People

Maholick, AW: AUTHOR [+2]

Abstract

In computer-connected output printers, when an error is detected by the printer, the host computer will be notified by an appropriate error status indication signal. The host computer will then solicit print job restart recovery information from the printer. Based on the information, the host processor can determine where it must resume transmission in the data that was sent in order to restart the job at the beginning of a new sheet of paper corresponding numerically to the page where the error occurred. If the printer is inoperative, the job may actually be re started on another printer since the information tells the host where to begin retransmission. The host processor insures that the first byte of data retransmitted begins at the specified checkpoint.

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Checkpointing for Printer Restart

In computer-connected output printers, when an error is detected by the printer, the host computer will be notified by an appropriate error status indication signal. The host computer will then solicit print job restart recovery information from the printer.

Based on the information, the host processor can determine where it must resume transmission in the data that was sent in order to restart the job at the beginning of a new sheet of paper corresponding numerically to the page where the error occurred. If the printer is inoperative, the job may actually be re started on another printer since the information tells the host where to begin retransmission. The host processor insures that the first byte of data retransmitted begins at the specified checkpoint. It also provides to the printer the checkpoint data necessary to resynchronize to the page on which printing is to resume. N pages are bypassed without printing by the printer to avoid duplicating those pages printed without error, from the checkpoint to the page on which the error occurred or a previous page.

In order to recover the job at the appropriate point, the host processor must insure that the first byte of data retransmitted begins as the one designated by the checkpoint register. Fig. 1 illustrates the basic concept. In this example, the data stream does not contain sequence numbers or the sequence numbers are not used. The printer counts valid data bytes that have been received since the previous reset interval as an offset delta(1), as shown in Fig. 1, until the checkpoint occurs. The checkpoint occurs every K pages at the first printed character following a page ejection as specified by the host processor checkpoint internal command. Its contents at checkpoint time are stored for usage by the host computer. A four-byte binary counter (not shown) can be used to contain this delta(1) offset count. So long as no transparent or compressed data is received, the counter accumulates each valid data byte. It will be reset only when the next set checkpoint interval is received.

Fig. 2 illustrates the more complicated case where...