Write-through-read (WTR) comparator circuits, systems, and methods use of same with a multiple-port file

• US 8,578,117 B2
• Filed: 02/10/2010
• Issued: 11/05/2013
• Est. Priority Date: 02/10/2010
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Burda, Gregory Christopher, McIlvaine, Michael Scott, Kolla, Yeshwant Nagaraj, Nunamker, Nathan Samuel
• Primary Examiner(s): Bradley, Matthew
• Assistant Examiner(s): Talukdar, Arvind
• Application Number:
  US12/703,342
• Publication Number:
  US 20110197021A1
• Time in Patent Office: 1,364 Days
• Field of Search: None
• US Class Current: 711/169
• CPC Class Codes: G06F 9/30141 Implementation provisions of register files, e.g. ports
• CPC Class Codes: G06F 9/3858 Result writeback, i.e. updating the architectural state or memory

Abstract

Write-through-read (WTR) comparator circuits and related WTR processes and memory systems are disclosed. The WTR comparator circuits can be configured to perform WTR functions for a multiple port file having one or more read and write ports. One or more WTR comparators in the WTR comparator circuit are configured to compare a read index into a file with a write index corresponding to a write-back stage selected write port among a plurality of write ports that can write data to the entry in the file. The WTR comparators then generate a WTR comparator output indicating whether the write index matches the read index to control a WTR function. In this manner, the WTR comparator circuit can employ less WTR comparators than the number of read and write port combinations. Providing less WTR comparators can reduce power consumption, cost, and area required on a semiconductor die for the WTR comparator circuit.

Claims

1. A circuit comprising:

a file comprising a plurality of read ports and a plurality of write ports, the file to store entries;

a processor pipeline comprising a plurality of stages, each stage having a corresponding write port, the file to store write-back stage data indicating which write port is to write to a given entry;

at least one WTR comparator configured to;

compare a read index indexing an entry in the file requested to be read and a write index corresponding to a selected write port, wherein the write-back stage data indicates the selected write port as writing to the entry;

generate a WTR comparator output indicating whether the write index matches the read index; and

a read data output selector configured to selectively generate a read data output of either write data to the file or read data from the file, based on the WTR comparator output.

2. The circuit of claim 1, wherein the at least one WTR comparator corresponds to the plurality of read ports.

3. The circuit of claim 1, wherein the write data corresponds to the selected write port.

4. The circuit of claim 1, wherein the at least one WTR comparator is comprised of a plurality of WTR comparators each corresponding to the plurality of read ports.

5. The circuit of claim 4, further comprising a plurality of write index selectors each configured to selectively provide the write index to one of the plurality of WTR comparators based on the write-back stage data for one of the plurality of read ports.

6. The circuit of claim 4, further comprising a plurality of read data output selectors each configured to selectively generate a read data output of either write data to the file or read data from the file, based on the WTR comparator output for one of the plurality of read ports.

7. The circuit of claim 1, wherein the at least one WTR comparator is comprised of a plurality of WTR comparators equal to or less than the plurality of read ports into the file.

8. The circuit of claim 1 integrated in at least one semiconductor die.

9. The circuit of claim 1, further comprising a device selected from the group consisting of a set top box, an entertainment unit, a navigation device, a communications device, a personal digital assistant (PDA), a fixed location data unit, a mobile location data unit, a mobile phone, a cellular phone, a computer, a portable computer, a desktop computer, a monitor, a computer monitor, a television, a tuner, a radio, a satellite radio, a music player, a digital music player, a portable music player, a video player, a digital video player, a digital video disc (DVD) player, and a portable digital video player, into which the circuit is integrated.

22. The circuit of claim 4, further comprising an encoder configured to provide encoded match lines for each read port.

10. A circuit comprising:

a file comprising a plurality of read ports and a plurality of write ports, the file to store entries;

a processor pipeline comprising a plurality of stages, each stage having a corresponding write port, the file to store write-back stage data indicating which write port is to write to a given entry;

a means for comparing a read index indexing an entry in the file requested to be read and a write index corresponding to a selected write port, wherein the write-back stage data indicates the selected write port as writing to the entry;

a means for generating a WTR comparator output indicating whether the write index matches the read index; and

a means to selectively generate a read data output of either write data to the file or read data from the file, based on the WTR comparator output.

11. A method of performing a write-through-read (WTR) compare, comprising:

storing entries in a file comprising a plurality of read ports and a plurality of write ports;

storing write-back stage data in the file to indicate which write port of the file is to write to a given entry;

comparing a read index indexing an entry in the file requested to be read and a write index corresponding to a selected write port, wherein the write-back stage data indicates the selected write port as writing to the entry;

generating a WTR comparator output indicating whether the write index matches the read index; and

selectively generating a read data output of either write data to the file or read data from the file, based on the WTR comparator output.

12. The method of claim 11, further comprising selecting the selected write port among the plurality of write ports into the file.

13. The method of claim 11, further comprising selectively providing the write index from a plurality of write indexes based on the write-back stage data.

14. A memory system, comprising:

a memory configured to store one or more entries, the memory comprising a plurality of read ports and a plurality of write ports;

a processor pipeline comprising a plurality of stages, each stage having a corresponding write port, the memory to store write-back stage data indicating which write port is to write to a given entry;

at least one write-through-read (WTR) comparator coupled to the memory and configured to;

compare a read index indexing an entry in the memory requested to be read and a write index corresponding to a selected write port, wherein the write-back stage data indicates the selected write port as writing to the entry;

generate a WTR comparator output indicating whether the write index matches the read index; and

a read data output selector configured to selectively generate a read data output of either write data to the memory or read data from the memory, based on the WTR comparator output.

15. The memory system of claim 14, wherein the memory is selected from the group consisting of a central processing unit (CPU) register file, a content-addressable memory (CAM), a cache memory, and a system memory.

16. The memory system of claim 14, wherein the read data output is coupled to a processor or a system bus.

17. The memory system of claim 14, further comprising a write index selector configured to selectively provide the write index based on the write-back stage data.

18. The memory system of claim 17, wherein the write-back stage data corresponds to a write-back stage in the processor pipeline in which the write data is provided to the memory.

19. The memory system of claim 14, wherein the at least one WTR comparator is comprised of a plurality of WTR comparators each corresponding to one of the plurality of read ports into the memory.

20. The memory system of claim 19, further comprising a plurality of write index selectors each configured to selectively provide the write index to one of the plurality of WTR comparators based on the write-back stage data for one of the plurality of read ports.

21. The memory system of claim 19, further comprising a plurality of read data output selectors each configured to selectively generate a read data output of either write data to the file or read data from the file, based on the WTR comparator output for one of the plurality of read ports.