Synchronizing data operations across a synchronization boundary between different clock domains using two-hot encoding

• US 6,366,530 B1
• Filed: 09/28/2001
• Issued: 04/02/2002
• Est. Priority Date: 04/09/2001
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: LSI Logic Corporation (Broadcom, Inc.)
• Inventors: Sluiter, David O., Moss, Robert W.
• Primary Examiner(s): Tran, Andrew Q.
• Application Number:
  US09/965,947
• Time in Patent Office: 186 Days
• Field of Search: 365/239, 365/240, 365/233, 365/230.06, 365/189.02, 365/189.07, 365/189.04, 365/189.05, 365/221
• US Class Current: 365/240
• CPC Class Codes: G06F 2205/102 Avoiding metastability, i.e. preventing hazards, e.g. by using Gray code counters
• CPC Class Codes: G06F 2205/106 Details of pointers, i.e. structure of the address generators
• CPC Class Codes: G06F 5/10 having a sequence of storage locations each being individually accessible for both enqueue and dequeue operations, e.g. using random access memory G06F5/065 takes precedence
• CPC Class Codes: G06F 5/14 for overflow or underflow handling, e.g. full or empty flags

Abstract

A digital logic circuit, such as a FIFO memory, includes pointers, or indicators, generated in two clock domains, between which information is transferred, to indicate a location in the digital logic circuit for transferring the information into or out of the digital logic circuit within either clock domain. Each pointer is encoded with a “2-hot” encoded value within one of the clock domains. The 2-hot encoded value of each pointer is sent to the other clock domain to synchronize the pointer to the other clock domain as well as to its original clock domain. Within each clock domain, the pointer generated therein and the pointer received from the other clock domain are used to determine whether the information can be transferred into or out of the digital logic circuit.

Claims

1. A circuit comprising:

a first pointer circuit configured to present a first pointer signal having a 2-hot encoding in response to a first clock signal;

a plurality of registers configured to store data in response to said first pointer signal; and

a selector circuit configured to select said data from said registers in response to a second clock signal.

2. The circuit according to claim 1, further comprising a first decoder circuit configured to present a first select signal having a 1-hot encoding in response to said first pointer signal to select among said registers for storing said data.

3. The circuit according to claim 2, further comprising an enable circuit configure to present an enable signal to said registers in response to said first select signal to enable one of said registers for storing said data.

4. The circuit according to claim 2, further comprising a second pointer circuit configured to present a second pointer signal having said 2-hot encoding in response to said second clock signal to control selection of said data from said registers.

5. The circuit according to claim 4, further comprising a second decoder circuit configured to present a second select signal having said 1-hot encoding to said selector circuit in response to said second pointer signal.

6. The circuit according to claim 4, further comprising a first synchronizer circuit configured to synchronize said first pointer signal to said second clock signal to present a first synchronized signal.

7. The circuit according to claim 6, further comprising a first generator circuit configured to present a first flag signal in response to said second pointer signal and said first synchronized signal.

8. The circuit according to claim 7, further comprising a second synchronizer circuit configured to synchronize said second pointer signal to said first clock signal to present a second synchronized signal.

9. The circuit according to claim 8, further comprising a second generator circuit configured to present a second flag signal in response to said first pointer signal and said second synchronized signal.

10. The circuit according to claim 1, wherein said plurality of registers is an odd number of registers.

11. A method of synchronizing data between a first clock signal and a second clock signal, the method comprising the steps of:

(A) generating a write signal having a 2-hot encoding in response to said first clock signal;

(B) storing said data among a plurality of storage units in response to said write signal; and

(C) selecting said data from said storage units in response to said second clock signal.

12. The method according to claim 11, further comprising the step of generating a first select signal having a 1-hot encoding in response to a first pointer signal to select among said storage units for storing said data.

13. The method according to claim 12, further comprising the step of generating an enable signal in response to said first select signal to enable one of said storage units for storing said data.

14. The method according to claim 12, further comprising the step of generating a second pointer signal having said 2-hot encoding in response to said second clock signal to control selection of said data from said storage units.

15. The method according to claim 14, further comprising the step of generating a second select signal having said 1-hot encoding in response to said second pointer signal to control selection of said data from said storage units.

16. The method according to claim 14, further comprising the step of synchronizing said first pointer signal to said second clock signal to present a first synchronized signal.

17. The method according to claim 16, further comprising the step of generating a first flag signal in response to said second pointer signal and said first synchronized signal.

18. The method according to claim 17, further comprising the step of synchronizing said second pointer signal to said first clock signal to present a second synchronized signal.

19. The method according to claim 18, further comprising the step of generating a second flag signal in response to said first pointer signal and said second synchronized signal.

20. A circuit comprising:

means for generating a write signal having a 2-hot encoding in response to a first clock signal;

means for storing data in response to said write signal; and

means for selecting among said data as stored in response to a second clock signal.