<12) United States Patent <10) Patent N0.: US 6,880,050 B1 Korger (45) Date of Patent: Apr. 12, 2005 (54) STORAGE DEVICE, SYSTEM AND METHOD 6,574,689 B1 * 6/2003 20101 et 01. ................. .. 710/52 WHICH CAN USE TAG BITS T0 SYNCHRONIZE QUEUING BETWEEN TWO EORETGN PATENT DOCUMENTS CLOCK DOMAINS, AND DETECT VALID 11> 10-112178 * 4/1998 .......... .. G11C/7/00
Primary Examiner—Matthew Anderson
Assistant Examiner—Shane Thomas
(74) Attorney, Agent, 0r Firm—Daffer McDaniel LLP
Asystem and method are presented for indicating active tag bits within valid entries of a dual-clock FIFO data buffer, used to transfer data between two clock domains. Data (containing tag bits) are written to the FIFO and read from the FIFO using separate clocks. Data writes are synchronous with the first clock, while reads are synchronous with the second clock. A FIFO entry is “valid” after data has been written to it, and before it is read. The system disclosed herein identifies the valid FIFO entries and generates a set of logic outputs, synchronized to the second clock (i.e., the read clock). Each output corresponds to one of the tag bit positions, and is HIGH if the corresponding tag bit is HIGH in any of the valid entries. This creates a means of detecting active tag bits in the FIFO without having to actually read each entry. Since the tag bits convey important information about the source and nature of the data, this detection system may expedite the data transfer. A simple implementation of the method is described, based primarily on conventional combinatorial logic. The method is straightforward and can readily be incorporated into an integrated circuit.
16 Claims, 3 Drawing Sheets
Inventor: Peter Korger, Frederick, CO (US)
Assignee: LSI Logic Corporation, Milpitas, CA
(U5)
Notice: Subject to any disclaimer, the term of this
patent is extended or adjusted under 35
U.S.C. 154(b) by 579 days.
Appl. No.: 09/702,202
Filed: Oct. 30, 2000
Int. Cl.7 ............................................. .. G06F 12/00
U.S. Cl. ........................................ .. 711/156; 710/55
Field of Search ............................... .. 711/147, 149,
711/156, 154; 710/52, 55, 57, 58; 365/189.01;
345/558
References Cited
U.S. PATENT DOCUMENTS
5,732,286 A * 3/1998 Leger ........................ .. 710/57
5,748,947 A * 5/1998 Fukushima . . . . . . . . .. 345/501
5,768,546 A * 6/1998 Kwon . . . . . . . . . . . . . . . .. 710/307
5,884,099 A * 3/1999 Klingelhofer .... .. 710/52
6,408,409 B1 * 6/2002 Williams et al. 714/719
6,433,787 B1 * 8/2002 Murphy . . . . . . . . . . . . .. 345/556
6,563,505 B1 * 5/2003 Mills et al. ............... .. 345/522
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