Logic block used as dynamically configurable logic function

• US 6,384,627 B1
• Filed: 02/16/2001
• Issued: 05/07/2002
• Est. Priority Date: 02/16/2001
• Status: Expired due to Fees

• Current Assignee: Xilinx, Inc. (Advanced Micro Devices, Inc.)
• Original Assignee: Xilinx, Inc. (Advanced Micro Devices, Inc.)
• Inventors: Fross, Bradley K., McGettigan, Edward S.
• Primary Examiner(s): Tokar, Michael
• Assistant Examiner(s): Tan, Vibol
• Application Number:
  US09/788,062
• Time in Patent Office: 445 Days
• Field of Search: 326/37-41
• US Class Current: 326/39
• CPC Class Codes: G06F 7/02 Comparing digital values G06F7/06, G06F7/22, G06F7/38 take precedence
• CPC Class Codes: G06F 7/026 Magnitude comparison, i.e. determining the relative order of operands based on their numerical value, e.g. window comparator
• CPC Class Codes: H03K 19/1736 in which the wiring can be modified
• CPC Class Codes: H03K 19/17752 for hot reconfiguration
• CPC Class Codes: H03K 19/17756 for partial configuration or partial reconfiguration

Abstract

A method of configuring an FPGA lookup table to implement both exact and relative matching comparators is disclosed. Examples of exact matching of two variables, exact matching of a variable to a constant, relative matching (greater than) of a variable to a constant, and combined exact and relative matching are discussed. Use of the comparator to trigger a logic analyzer to collect data is discussed.

Claims

1. In an FPGA, comprising:

I. a general interconnect structure; and

II. an array of logic blocks, each logic block comprising;

a. a lookup table configurable as a shift register, the lookup table having a shift register input terminal, a plurality of data input terminals and an output terminal;

b. a carry multiplexer controlled by the output terminal of the lookup table, having

i. an output terminal,

ii. a first input terminal that may be coupled to the output terminal of another carry multiplexer, and

iii. a second input terminal;

c. an AND gate having an output terminal connectable to the second input terminal of the carry multiplexer and two input terminals connected to two of the plurality of data input terminals of the lookup table;

a programmable comparator for comparing at least one value on at least one of the plurality of input terminals of the lookup table to at least one other value, the programmable comparator having two modes, a loading mode and an operating mode, wherein

in the loading mode a clock signal causes a bitstream to be shifted from the shift register input terminal into the lookup table; and

in the operating mode the bitstream in the lookup table performs a comparison function implemented such that a successful comparison causes the carry multiplexer to connect to its output terminal an input terminal whose value represents the successful comparison, and a failed comparison causes the carry multiplexer to connect to its output terminal an input terminal whose value represents a failed result.

2. The programmable comparator of claim 1 wherein the comparison comprises an exact match type of comparison, and a successful comparison causes the carry multiplexer to connect the first input terminal to the output terminal and a failed comparison causes the carry multiplexer to connect the second input terminal to the output terminal.

3. The programmable comparator of claim 2 wherein at least one of the plurality of inputs is compared with a “

don'"'"'t care”

constant value.

4. The programmable comparator of claim 2 wherein the programmable comparator determines that a successful comparison occurs when the value on one of the plurality of input terminals is equal to another value on another one of the plurality of input terminals.

5. The programmable comparator of claim 2 wherein the programmable comparator determines that a successful comparison occurs when the value on one of the plurality of input terminals is equal to a constant stored in the lookup table.

6. The programmable comparator of claim 2 wherein the programmable comparator determines that a successful comparison occurs when the value on one of the plurality of input terminals is not equal to a constant stored in the lookup table.

7. The programmable comparator of claim 1 wherein the comparison comprises a relative match type of comparison, and a successful comparison of “

equal to”

causes the carry multiplexer to connect the second input terminal to the output terminal, a successful comparison of “

greater than”

causes the carry multiplexer to connect the first input terminal to the output terminal, and a failed comparison causes the carry multiplexer to connect the first input terminal to the output terminal.

8. The programmable comparator of claim 7 wherein the programmable comparator determines that a successful comparison occurs when the value on one of the plurality of input terminals is greater than a constant stored in the lookup table.

9. The programmable comparator of claim 7 wherein the programmable comparator determines that a successful comparison occurs when the value on one of the plurality of input terminals is not greater than a constant stored in the lookup table.

10. The programmable comparator of claim 7 wherein the programmable comparator determines that a successful comparison occurs when the value on one of the plurality of input terminals is less than a constant stored in the lookup table.

11. The programmable comparator of claim 7 wherein the programmable comparator determines that a successful comparison occurs when the value on one of the plurality of input terminals is not less than a constant stored in the lookup table.

12. The programmable comparator of claim 1 wherein the lookup table configurable as a shift register further has a shift register output terminal connectable to the shift register input terminal of another one of the logic blocks in the array.

13. The programmable comparator of claim 1 wherein when the programmable comparator is in the loading mode, the plurality of data input terminals each receive an input signal that cause the output terminal of the lookup table configurable as a shift register to be connected to a last memory cell in the shift register, and wherein the output terminal of the lookup table is connected to the shift register input terminal of another lookup table.

14. The programmable comparator of claim 13 wherein the modes of the comparator are controlled by a configuration enable signal that disables the shift registers when in operating mode.

15. The programmable comparator of claim 13 wherein the plurality of data input terminals of the lookup table are each connected to an output terminal of a flip flop and the configuration enable signal is connected to an asynchronous reset terminal of each flip flop.

16. The programmable comparator of claim 1 wherein the comparator includes a last multiplexer at an end of a chain of all multiplexers in the comparator that generates a comparator output signal and wherein this comparator output signal triggers a logic analyzer in the FPGA to start collecting data.

17. An FPGA configuration wherein a portion of the configuration is a logic analyzer for providing information to a user about operation of another portion of the configuration, and wherein part of the configuration of the logic analyzer is determined when the FPGA is configured and another part of the configuration of the logic analyzer is determined by another portion of the logic analyzer.

18. The FPGA of claim 17 wherein the part of the configuration of the logic analyzer determined by another portion of the logic analyzer includes a value stored in at least one lookup table.

19. The FPGA of claim 18 wherein the lookup table is connectable as a shift register and configured by loading a bitstream through the shift register.

20. The FPGA of claim 18 wherein the at least one lookup table comprises a plurality of lookup tables.

21. The FPGA of claim 18 wherein the plurality of lookup tables are loaded by shifting a bitstream through a shift register.