United States Patent m
Dearth et al.
[54] DMA CONTROLLER FOR MEMORY SCRUBBING
[75] Inventors: Glenn Dearth, Groton; Thomas D.
Bissett, Northboro, both of Mass.
[73] Assignee: Digital Equipment Corporation,
Maynard, Mass.
[21] Appl. No.: 603,968
[22] Filed: Feb. 20,1996
Related U.S. Application Data
[63] Continuation of Ser. No. 998,717, Dec. 30, 1992, abandoned.
[51] Int. CI.6 G06F 11/34
[52] U.S. CI 395/182.07; 395/842; 371/40.2
[58] Field of Search 395/182.03, 181,
395/182.04, 182.07, 185.01, 185.07, 842; 371/40.1, 40.2, 40.4; 364/242.31, 242.3,
242.34
[56] References Cited
U.S. PATENT DOCUMENTS
4,488,228 12/1984 Grudele et al 364/200
4,604,750 8/1986 Manton et al 371/38
4,672,613 6/1987 Foxworthy et al 371/38
IIIIIIUIillllllilllilllllllllllMlllllllllllllll
US005588112A
[li] Patent Number: 5,588,112 [45] Date of Patent: Dec. 24, 1996
4,682,328 7/1987 Ramsay et al 371/51.1
4,733,396 3/1988 Baldwin et al 371/38
4,821,170 4/1989 Bernick et al 364/200
4,888,773 12/1989 Arlington et al 371/40.2
4,905,242 2/1990 Popp 371/38
4,907,228 3/1990 Bruckert et al 371/68.3
5,068,780 11/1991 Bruckert et al 395/700
5,072,450 12/1991 Helm et al 371/26.1
5,274,645 12/1993 Idleman et al 371/10.1
Primary Examiner—Robert W. Beausoliel, Jr.
Assistant Examiner—Albert Decady
Attorney, Agent, or Firm—Denis G. Maloney; Arthur W.
Fisher
[57] ABSTRACT
A fault tolerant computer system is described in which a direct memory access controller examines the check bit data on every data element that is accessed by the system. The address of any data element that is found to have an error in the check bit data is stored by the direct memory access controller, the check bit data is used by the direct memroy access controller to correct the error, and the corrected data element is rewritten to the original storage address. By the use of this arrangement, the central processing unit or units of the computer system are free to perform other tasks, thus improving system throughput, and preventing the accumulation of data element errors in the memory.
20 Claims, 26 Drawing Sheets
