[54] HOST SIGNAL PROCESSING
COMMUNICATION SYSTEM THAT
COMPENSATES FOR MISSED EXECUTION
OF SIGNAL MAINTENANCE PROCEDURES
[75] Inventors: Han C. Yeh, Sunnyvale; Peter C.
Chen, Saratoga, both of Calif.
[73] Assignee: PC-Tel, Inc., Santa Clara County, Calif.
[21] Appl. No.: 527,668
[22] Filed: Sep. 12,1995
[51] Int. CI.6 G06F 13/00
[52] U.S. CI 395/200.67; 395/872
[58] Field of Search 395/500.200.12.
395/250, 497.01. 821, 872, 889. 200.57, 200.6. 200.67; 379/93, 97, 58, 77, 79
[56] References Cited
U.S. PATENT DOCUMENTS
4,972,411 11/1990 Fushimi et al 370/522
4,991,169 2/1991 Davis et al 370/463
4,995,074 2/1991 Goldman et al 379/97
5,375,228 12/1994 Leary et al 395/183.09
Primary Examiner—Parshotam S. Lall
Assistant Examiner—Viet Vu
Attorney, Agent, or Firm—Skjerven. Morrill, MacPherson.
Franklin & Friel; David T. Millers
[57] ABSTRACT
An HSP communications system contains a host computer which executes a software modem program and a device containing a circular buffer and a D/A converter. Typically, the host executes update routines in response to interrupts from the device and writes to the circular buffer digital samples representing amplitudes of an analog signal complying with a desired communication protocol. The samples pass through the circular buffer to the D/A converter which converts the samples into an analog communication signal. In environments such as multi-tasking systems, the host may occasionally skip interrupts and not provide new samples when required. In mis case, the D/A converter reuses samples in the circular buffer to generate a maintenance signal. The maintenance signal typically does not convey correct data but is sufficient to maintain a communication link and prevent a remote device from disconnecting or entering a retrain mode. To provide a smoother maintenance signal, the circular buffer's size contains samples for an integral number of periods at the carrier and baud frequency of the desired protocol. Error correction and retransmission replace incorrect or lost data.
23 Claims, 9 Drawing Sheets
