U.S. patent application number 12/148071 was filed with the patent office on 2008-08-14 for method and apparatus for universal program controlled bus architecture.
Invention is credited to Peter M. Pani, Benjamin S. Ting.
Application Number | 20080191739 12/148071 |
Document ID | / |
Family ID | 24845670 |
Filed Date | 2008-08-14 |
United States Patent
Application |
20080191739 |
Kind Code |
A1 |
Pani; Peter M. ; et
al. |
August 14, 2008 |
Method and apparatus for universal program controlled bus
architecture
Abstract
An integrated circuit including a programmable logic array with
a plurality of logic cells and programmable interconnections to
receive input signals and to perform logical functions to transmit
output signals. The integrated circuit may also include megacells
comprising a plurality of functional blocks receiving inputs and
transmitting outputs. The integrated circuit may also include a
programmable interconnections subsystem to cascade the megacells.
The megacells are coupled to the programmable logic array.
Inventors: |
Pani; Peter M.; (Mountain
View, CA) ; Ting; Benjamin S.; (Saratoga,
CA) |
Correspondence
Address: |
BLAKELY SOKOLOFF TAYLOR & ZAFMAN LLP
1279 OAKMEAD PARKWAY
SUNNYVALE
CA
94085-4040
US
|
Family ID: |
24845670 |
Appl. No.: |
12/148071 |
Filed: |
April 15, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11219597 |
Sep 1, 2005 |
7382156 |
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12148071 |
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10811422 |
Mar 25, 2004 |
6975138 |
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11219597 |
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10412975 |
Apr 11, 2003 |
6781410 |
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10811422 |
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10231320 |
Aug 28, 2002 |
6624658 |
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10412975 |
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09960916 |
Sep 24, 2001 |
6504399 |
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10231320 |
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09243998 |
Feb 4, 1999 |
6329839 |
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09960916 |
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08708403 |
Sep 4, 1996 |
6034547 |
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09243998 |
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Current U.S.
Class: |
326/39 |
Current CPC
Class: |
H03K 19/17736 20130101;
H03K 19/17704 20130101; H03K 19/17728 20130101; H03K 19/17796
20130101; H03K 19/17744 20130101 |
Class at
Publication: |
326/39 |
International
Class: |
H03K 19/177 20060101
H03K019/177 |
Claims
1. An integrated circuit, comprising: a programmable logic array
comprising: a plurality of logic cells; and programmable
interconnections to receive digital input signals and to perform
logical functions to transmit digital output signals; a megacell
comprising a plurality of functional blocks receiving digital
inputs and transmitting digital outputs, wherein the megacell does
not exclusively perform a memory function; and a programmable
interconnections subsystem to provide communication between the
programmable logic array and the megacell.
2. The integrated circuit as set forth in claim 1, wherein the
megacell is implemented using programmed metal masks.
3. The integrated circuit as set forth in claim 1, wherein the
megacell is implemented using customized masks.
4. A method, comprising: performing a processing function by a
megacell; and communicating digital signals between the megacell
and a programmable logic array using a programmable interconnection
subsystem.
5. The method of claim 4, further comprising selecting, within the
programmable interconnection subsystem, one of the digital signals
using tri-statable logic control for at least one of input to or
output from the megacell.
6. The method of claim 4, further comprising selecting, within the
programmable interconnection subsystem, one of the digital signals
using tri-statable logic control for at least one of input to or
output from the programmable logic array.
7. The method of claim 4, further comprising programming the
programmable interconnection subsystem to enable the communicating
of the digital signals.
8. The method of claim 6, further comprising providing a tri-state
to the logic control in the programmable interconnection subsystem
to enable the communicating.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 11/219,597 filed Sep. 1, 2005, which is a continuation of U.S.
application Ser. No. 10/811,422 filed Mar. 25, 2004, U.S. Pat. No.
6,975,138, which is a continuation of U.S. application Ser. No.
10/412,975 filed Apr. 11, 2003, U.S. Pat. No. 6,781,410, which is a
continuation of U.S. application Ser. No. 10/231,320 filed Aug. 28,
2002, U.S. Pat. No. 6,624,658, which is a continuation of U.S.
application Ser. No. 09/960,916 filed Sep. 24, 2001, U.S. Pat. No.
6,504,399, which is a continuation of U.S. application Ser. No.
09/243,998 filed Feb. 4, 1999, U.S. Pat. No. 6,329,839, which is a
continuation of U.S. application Ser. No. 08/708,403 filed Sep. 4,
1996, U.S. Pat. No. 6,034,547.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention is directed to a programmable,
configurable bus system of lines to interconnect electrical
components for an electrical/electronics system.
[0004] 2. Art Background
[0005] Megacells are described as block components such as static
random access memory (SRAM), microcontrollers, microprocessors and
buffers. Sometimes it is desirable to interconnect a plurality of
megacells together to provide a larger functional entity. One way
to interconnect multiple megacells and logic circuits is through a
hardwired bus system. Examples are illustrated in FIGS. 1a, 1b and
1c. FIG. 1a illustrates a bus interface to a dual port SRAM
megacell. Bus lines include DATA0-DATA15, READA0-READA9,
WRITEA0-WRITEA9. To couple multiple megacells, the data lines are
shared among the coupled cells. However, separate read and write
lines would be required for each megacell. To the contrary, if the
megacells were coupled to generate a deeper combined megacell, the
data lines would be separate for each megacell and the read and
write lines would be shared among the megacells. Control signals
are then be used to select a particular megacell for a particular
operation. This is illustrated in FIGS. 1b and 1c.
[0006] Such configurations are hardwired and cannot easily be
changed to accommodate different configurations. Furthermore, if
errors occur in the mask generated, repairs are not easily made, as
configurability is minimal. In addition to providing a bus system
to interconnect multiple megacells, tristatable input ports are
sometimes used to enable multiple inputs to be input to a
particular bus line thus allowing a system level communication
between logic to megacells or megacells to megacells. However, a
single tristate can directly couple to only one line.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] The objects, features and advantages of the present
invention will be apparent to one skilled in the art from the
following detailed description in which:
[0008] FIGS. 1a, 1b and 1c illustrate interconnections of prior art
megacells.
[0009] FIGS. 2A and 2B illustrate one embodiment in which logic is
programmably coupled to the megacell.
[0010] FIG. 3 is a block diagram illustration of exemplary
programmable logic utilized to implement one embodiment of the
configurable bus system of the present invention.
[0011] FIGS. 4A and 4B illustrate the organization of the
programmable logic of FIG. 3.
[0012] FIGS. 5A and 5B provide further illustration of the
organization of the programmable logic of FIG. 3.
[0013] FIG. 6 illustrates the programmability of connections to
bussed signal lines to multiple megacells in accordance with the
teachings of the present invention.
[0014] FIG. 7a is a block diagram illustration of one embodiment of
a megacell connected to the bus system and I/O.
[0015] FIG. 7b illustrates one embodiment of a dual-port static
random access memory (SRAM) megacell with a field programmable gate
array (FPGA).
[0016] FIG. 8a is a block diagram illustration of an alternate
embodiment and FIG. 8b illustrates the embodiment incorporated into
a dual port SRAM with a FPGA.
DETAILED DESCRIPTION
[0017] The system of the present invention provides a flexible
programmable bus structure system of lines to couple one or more
circuits for input and output as well as to each other. In the
following description, for purposes of explanation, numerous
details are set forth in order to provide a thorough understanding
of the present invention. However, it will be apparent to one
skilled in the art that these specific details are not required in
order to practice the present invention. In other instances, well
known electrical structures and circuits are shown in block diagram
form in order not to obscure the present invention
unnecessarily.
[0018] One embodiment of the programmable bus system is illustrated
in FIGS. 2A and 2B. The system is illustrated using a megacell
circuit; however, it is readily apparent that the system can be
utilized with a variety of types of circuits and/or components. The
type of megacell component used in the following discussion is a
256.times.8 dual port static random access memory (SRAM). However,
the bus system described herein is not limited to SRAM components.
A variety of components, such as microcontrollers, buffers, digital
signal processors (DSPs) can be coupled to the bus system described
herein.
[0019] FIGS. 2A and 2B illustrate one embodiment of the
configurable bus system of the present invention. Referring to
FIGS. 2A and 2B, the configurable bus system of lines includes
groups of lines 210, lines 215, and lines 220, 225. Each data
input/output port of the megacell 205 is connected to one line of
lines 210. For example, DI[0] is connected to Data[0], DI[1] is
connected to Data[1], etc. In addition, each read or write address
port of the megacell 205 is connected to one of the group of lines
215. Furthermore, lines 225 are connected to the control ports of
the megacell 205. It is recognized that the exemplary system
described herein has been programmed to convey address, data and
control information across certain of the lines which form the bus
system of lines. It is readily apparent that in other applications
the system may only convey other combinations of information such
as data and control. In addition, one skilled in the art recognizes
that the lines are programmable and can be configured for a variety
of types of information in addition to the types of information
described herein.
[0020] In the present embodiment, data is preferably input to the
megacell 205 and output from the megacell through interface logic
230. As will be described below, the interface logic is embodied in
a programmable logic device, such as a field programmable gate
array (FPGA); however, other types of logic can be used. A first
set of programmable connections programmably couple the interface
logic 230 to the data input/output ports of the megacell 205 (e.g.,
elements 235, 240, 245, 250). For example, programmable elements
235, 240 selectively connect a first line 255 from the interface
logic 230 to lines Data[0] 211 and Data[8] 212. In addition, in the
present embodiment, the programmable elements of the first set of
programmable elements programmably couple the interface logic 230
to line 215. For example, programmable elements 237, 247
selectively connect a first line 256 from the input/output logic
230 to bussed lines READA[0] 216 and WRITEA[0] 217. Furthermore,
the location of the programmable elements and the lines that each
programmable element selectively connect to can be varied according
to application. FIGS. 2A and 2B illustrate one arrangement of
programmable elements of the first set of programmable elements
that provides flexibility in configuring the bus system of
lines.
[0021] The control signals to the megacell 205 can be similarly
transmitted over the configurable bus system described herein. A
second set of programmable connections are used to selectively
connect control signals received from the interface logic 230 to
the lines 225 and megacell 205. For example, programmable elements
261, 262 selectively connect a global clock input to lines 226,
227. In addition, in the present embodiment, lines READA[8],
READA[9], WRITEA[8], WRITEA[9] (220 collectively) are used to
provide the higher order address bits as control inputs to select
other coupled megacells. This illustrates the capability of this
innovative bus system to provide system level integration.
[0022] Preferably, a third set of programmable connections are used
to selectively extend the number of megacells coupled to the
configurable bus system. The bus system is configurable using
elements of the third set of programmable connections to
selectively connect on or more megacells to the bus system of
lines. The third set of programmable connections selectively limit
the load on the lines for better performance by extending the lines
(and therefore increasing the load) only when needed. In the
present embodiment, for example, programmable elements 270, 271
selectively extend the lines 210 and lines 215.
[0023] In addition, it is preferred that the interface logic 230 is
programmable and provides bidirectional access to the bus. In
addition, it is preferably that the interface logic provides
three-statable control to the bus. In particular, control bits and
associated logic is used to provide bidirectional, three state
control and selective input/output of a plurality of external
connections to the lines of the bus system. Referring to FIG. 2,
the input/output logic 230 includes a plurality of elements, e.g.,
231, 232, 233, 234. Each element is coupled to two external
connections 280, 281. Each element is further coupled to enable
control signals, e0 282, e1 283. The enable control signals e0, e1
and control bits 284, 285 function to provide the three state bus
functionality that selects one of two external connections for
input to or output from the bus. Control bit 284 controls the
connection as input to the megacell 205 and control bit 285
controls the connection as output from the megacell 205. If the
control bit 284 is set to a first state, e.g., zero, the
three-state connection is disabled. If the control bit 284 is set
to a second state, e.g., 1, the state of the connection is
controlled by enable control signals e0, e1. Although the present
embodiment incorporates the bidirectional, three state access to
the bus system of lines, it is contemplated that bidirectional
three state access mechanism is implemented separate form the
interface logic.
[0024] The programming of the bus system of lines can be achieved a
variety of ways. One method is to manually program the different
programmable connections associated with particular lines of the
bus system of lines. Other automated methods are also contemplated.
Obviously, once programmed, the programmable connections can remain
in the programmed state. Alternately, a dynamic programmable system
can be provided wherein control circuitry coupled to the bus system
and the programmable connections can determine, prior to a data
transfer, those connections to program in order to configure the
bus system of lines to transfer the data. This control circuitry
could reside in a circuit coupled to the bus system for the
transfer of data or in a circuit external to the bus system and
connected circuits. For example, the bus system may couple a
processor or arithmetic logic unit and memory. The processor or ALU
can contain the control circuitry to configure the bus for each
data transfer or plurality of transfers.
[0025] Furthermore, it is contemplated that the connections to be
programmed can be determined a variety of ways in order to
configure the bus system for a general transfer or specific
transfers of data. For example, the control circuitry could examine
the content of the data to be transferred and the control signals
issued prior to or contemporaneous with a request to transfer or a
signal indicating data is to be transferred (e.g., read or write
signals or commands) to determine the programmable connections to
be programmed.
[0026] The bus system described can be used to connect components,
logic circuits and the like which span across one or more elements.
In the present example, as noted above, the bus system is used to
connect memory (SRAM) to the logic of a programmable logic device
(PLD) such as a field programmable gate array (FPGA). More
particularly, in the present embodiment, the bus system is used to
integrate the memory into the same component as the FPGA. The FPGA,
embodied as the interface logic in the present embodiment,
preferably functions as control logic for accessing the SRAM or as
interface logic between the SRAM and other devices. Preferably, a
programmable logic device such as those described in U.S. Pat. No.
5,457,410 and U.S. patent application Ser. No. 08/534,500, filed
Sep. 27, 1995 is used.
[0027] FIG. 3 is a block diagram of an exemplary FPGA 300. The I/O
logic blocks 302, 303, 311, and 312 provide an interface between
external package pins of the FPGA 300 and the internal user logic
either directly or through the I/O to Core interface 304, 305, 313,
314. The external package pins are coupled to the lines of bus
system (210, 215, FIG. 2), the signals that are processed through
the input/output logic (230 FIG. 2), and the ports of the megacell
(205, FIG. 2). Four interface blocks 304, 305, 313 and 314 provide
decoupling between core 306 and logic 302, 303, 311 and 312.
[0028] The Core 306 includes configurable logic and an interconnect
hierarchy. In the present embodiment, the logic is organized in a
number of clusters 307 of logic which are intraconnected by an
I-Matrix 301 and interconnected by MLA routing network 308. The
core also includes control/programming logic 309 to control the
bits for programming the intraconnection and interconnection lines.
In the embodiment described herein, SRAM technology is utilized.
However, fuse or antifuse, EEPROM/ferroelectric or similar
technology may be used. In order to minimize skewing, a separate
clock/reset logic 310 is used to provide clock and rest lines on a
group basis.
[0029] The present embodiment provides logic in groups called
clusters. FIG. 4a is an example of a logic cluster. It is
contemplated that the logic cluster illustrated by FIG. 4a is
illustrative and logic cluster can be formed of other elements such
as logic gates and flip-flops. Referring to FIG. 4a, the logic
cluster 400 is formed of four logic elements. These elements
include one 2 input combinational logic or configurable function
generator (CFG) 402, two three input CFGs 404, 406 and D flip-flop
408. CFG 402 can also be a three input CFG. The CFGs 402, 404, 406
are programmable combinatorial logic that provide a predetermined
output based using two input values (for CFG 402) or three input
values (for CFGs 404, 406). The CFGs are programmed with values to
provide output representative of a desired logic function. The D
flip flop 408 functions as a temporary storage element such as a
register.
[0030] This combination of one two input, one output CFG, two three
input one output CFGs and a D flip flop enable a variety of logic
and arithmetic functions to be performed. For example, the elements
can be programmed to perform such functions as comparator functions
or accumulator functions. In the present embodiment, it is used to
selectively couple bus signal lines to input/outputs of a megacell
and to input/output logic. It should be noted that this combination
of elements provides a fine granularity without the addition of
redundant elements which add to the die size and speed of
processing. Furthermore, the combination of elements also maximizes
usage of elements thereby maximizing usage of die size space. The
fine granularity characteristic resulting in more output points
that can be tapped is a desirable characteristic as often an
intermediate signal generated by a particular combination of
elements is needed.
[0031] In addition, the local interconnect within the cluster is
structured to enable signals to be processed within minimum delays.
The cluster elements, 402, 404, 406, 408, are connected through
interconnection lines I-M0 through I-M5 (referred to herein
collectively as I-Matrix lines) which are oriented horizontally and
vertically through the logic cluster. These intraconnections of a
cluster are programmable through switches, for example switches
420-444. Intraconnections lines I-M0 to I-M5 and switches 420-444
form what is referred to herein as the I-Matrix. The I-Matrix
provides connectability among the elements 402, 404, 406, 408 to at
least one other element of the cluster. For example, the output of
the CFG 202 can be connected to the input of CFG 404 by enabling
switches 424 and 428.
[0032] To ensure minimum signal delays during processing, separate,
direct connections are provided between the D flip flop 408 and the
three input CFGs 404, 406. Continuing reference to FIG. 4a,
switches 450-455 and connected lines provide such connections. It
has been determined that the input and output of the three input
CFGs 404, 406 often perform programmed functions in conjunction
with the register 408. For example the three input CFGs can be
utilized with the register to provide a one bit multiplexing
function.
[0033] The bi-directional switches 450-455 can be programmed a
variety of ways to route the signal to achieve a specific function.
For example, a signal output by CFG 404 can drive D flip-flop 408
by enabling switch 451. Alternately, the signal may be driven onto
the I-Matrix by enabling switch 450. Similarly, the output of CFG
406 can drive the input of the D flip-flop 408 by enabling switch
455. Other routing paths by selectively enabling switches are also
possible. Furthermore, the output of the CFG 402 can drive the D
flip-flop 408 by an indirect connection through the I-Matrix. thus,
extreme flexibility is achieved.
[0034] The routing of the output signal of the D flip-flop is also
programmable through switches 452 and 453. By selectively enabling
switches 452 or 453 and selective switches of the I-Matrix, the
output signal can be routed to any one of the elements of the
cluster or of other clusters. The signal output is selectively
routed through the switches 433-435 adjacent to the CFG 204 or to
switches 441, 442 and 443 adjacent to CFG 406. Die savings are
achieved without decreasing the level of usage of elements in the
device.
[0035] Each logic cluster is connectable to the other logic
clusters inside the logic block through switches extending the
I-matrix between neighboring clusters. FIG. 4b illustrates I-matrix
interconnection lines I-M0 to I-M5 of a first logic cluster 460
selectively connected to the I-Matrix lines of adjacent logic
clusters 461 and 463, respectively through switches 464, 465, 466,
467, 475 and 476.
[0036] The flexibility herein described is partially achieved
through the numerous bi-directional switches used. It was also
noted previously that the switches can be implemented a variety of
ways. For example, the switches can be implemented as fusible links
which are programmed by blowing the fuse to open or short the
switch. Alternately, the switch can be a passgate controlled by a
bit in an SRAM array. The state of the bits in the array dictate
whether a corresponding passgates are open or closed.
[0037] To allow an efficient implementation of a carry chain as
well as other applications, staggered or barrel connections between
clusters is used to increased connectivity. FIG. 4b illustrates the
extensions of the I-Matrix within a logic cluster to neighboring
clusters. For example, switch 475 connects I-M5 of cluster 460 to
I-M0 of cluster 461 and switch 476 connects I-M1 of cluster 460 to
I-M2 of cluster 461.
[0038] A plurality of interconnected logic clusters form a logic
block. In the present embodiment each logic block consists of four
logic clusters organized in a 2.times.2 array as generally
illustrated by FIG. 5a. Each logic block has a set of
bi-directional routing lines to which all CFGs inside the logic
clusters are programmably connected. The bi-directional routing
line provide the path for signals to travel into and out of the
logic block to the routing lines of a hierarchical routing
architecture having multiple lengths of interconnections at
different levels of the hierarchy. It can also be seen that the
block connectors can also provide connections among the CFGs of the
logic clusters of the same block and adjacent blocks. Although the
input and output of each element of each logic cluster of the logic
block can be selectively connected to each block connector, to
control the expansion on die size it is preferred that each input
and output is selectively connected to a subset of block
connectors. An example of such an embodiment is shown in FIG.
5b.
[0039] Referring to FIG. 5b, a symbolic representation of one
embodiment of the connections to block connectors within a block
300 is shown. Each element of each cluster 500, e.g., CFG1, CFG2
and CFG3 is connected to two identified block connectors (BC) at
the inputs. Two block connectors are identified as coupled to the
output of the two input CFG1 and three block connectors are coupled
to the output of the three input CFGs (CFG2, CFG3). The specific
block connectors coupled to each elements are distributed among the
elements of the block to maximize connectivity.
[0040] The block connectors provide the input and output mechanism
for interconnecting to higher levels of connections of the routing
hierarchy referred to as the multiple level architecture (MLA)
routing network. The network consists of multiple levels of routing
lines (e.g., MLA-1, MLA-2, MLA-3, MLA-4, etc.) organized in a
hierarchy wherein the higher level routing lines are a multiple
longer than the lower level routing lines. For example, MLA-2
routing lines are twice as long as MLA-1 routing lines and MLA-3
routing lines are twice as long as MLA-2 routing lines and MLA-4
routing lines are twice as long as MLA-3 routing lines.
[0041] Using the logic and interconnect hierarchy described, the
user can program the PLD and the bus to access the memory in a
variety of configurations without requiring significant space on
the component.
[0042] The flexibility and utility of the configurable bus system
of the present invention is illustrated with reference to FIG. 6.
FIG. 6 shows the bus system configured to couple to 4 SRAM
megacells arranged in a 2.times.2 configuration. The programmable
elements are configured as passgates controlled by a bit in one of
the SRAMs or other coupled memory. As is illustrated, no extra
logic or interconnect is required for the bus system configuration.
By enablement of the proper links which control the interconnect,
the bus system is easily configured for the particular arrangement
of megacells.
[0043] In the present example, the bus system is programmed to be
coupled to the interconnect of the PLD (e.g., block connectors
(bc), I-matrix lines (IM) and MLA lines (MLA-1)) to enable the
logic of the PLD to provide the necessary interface logic to
interface the SRAM to components or devices external to the system.
For example, the PLD provides logic to assert the necessary control
signals to transmit the address information and receive and
transmit data. In the example shown in FIG. 6, data and address
information is communicated through the bi-directional block
connectors. Control information, including control signals to
control the state of the enable signals (e0, e1) are communicated
via the I-matrix and MLA-1 lines.
[0044] FIG. 7a is a block diagram illustration of one embodiment of
megacell 701, 702, coupled to the bus system of the present
invention. A program controlled interface 703, 704, to the bus
system of lines 705 and megacells 701, 702 are provided. The
interface from the core bus 705 to the I/O 706, 707 can be achieved
using hardwired or program controlled connections 708, 709.
Preferably, these connections are achieved using a programmable,
peripheral bus system of lines 710, 711 to provide further
flexibility. The peripheral bus system is preferably programmable
in the same manner as described above with respect to FIG. 2. In
the present embodiment, the interface logic (230 FIG. 2) provides
the program controlled interface 703, 704 to the bus system 705
which is also programmed controlled.
[0045] FIG. 7b depicts an overview of an exemplary component
configured with dual port SRAM megacells and a FPGA. The FPGA,
including its interconnect structure, is represented by elements
712, 715, 720, 725. Each element 712, 715, 720, 725 comprises a
plurality of logical blocks organized in 16.times.16 array with a
corresponding hierarchical interconnect structure as discussed in
U.S. Pat. No. 5,457,410 and U.S. patent application Ser. No.
08/534,500. The FPGA elements 712, 715, 720, 725 are connected by
the interconnect, e.g., block connectors, I-matrix lines and MLA
lines (see FIG. 6), through the configurable bus system of lines
(e.g., as represented by elements 730, 735, 740) to an SRAM (e.g.,
745, 750, 755, 760). SRAM 745, 750, 755, 760 and elements 730, 735
and 740 correspond to the structure illustrated by FIG. 6. It
should be noted that the bus system preferably spans the entire
component to the adjacent array of SRAMs 775, 780, 785, 790 through
programmable elements (not shown). The bus system is further
coupled to I/O ports or pads (e.g., 791, 792) for input/output
to/from the system to external components or devices. Although the
bus system can be coupled through hardwired connections, it is
preferred that the connection be made via programmable elements,
e.g., 765, 770 and bus system of lines 775.
[0046] FIG. 8a is a block diagram illustration of an alternate
embodiment in which gateway interface logic 801 is used to
interface the core bus system 802 to the I/O 803. In addition, this
diagram illustrates alternative programmable connections that can
be implemented to provide further programmability and flexibility
to the system.
[0047] The gateway interface logic 800 is composed of hardwired
logic, metal programmable logic, or programmable logic such as a
plurality of logic clusters and is directly or indirectly coupled
(i.e., direct hardwired connections or indirect program controlled
connections) to the megacell 804. FIG. 8a shows the gateway
interface logic 800 is coupled to the megacell 804 via peripheral
bus 805 which preferably includes bi-directional, three-statable
connections (e.g., 808). The gateway interface logic 800 provides
an additional level of logic to the interface between the megacell
and the I/O pads or ports to external components or devices. The
gateway interface logic can enable faster transfer of information.
For example, the gateway interface logic can be structured to
provide the specific bus protocols or handshaking required to
interface to external devices. The gateway interface logic can also
provide address decode functionality (e.g., wide decode) to
expedite processing of information.
[0048] In the present embodiment, the gateway interface logic 800
is implemented as a logic cluster 801, consistent with the logic
clusters referred to herein and in U.S. Pat. No. 5,457,410 and U.S.
patent application Ser. No. 08/534,500. I-Matrix lines are used to
connect the gateway logic to the peripheral bus 805. It should be
recognized that the gateway interface logic is not limited to the
specific implementation described herein and a variety of logic
implementations can be used.
[0049] FIG. 8b illustrates dual port SRAMs with FPGA and the
configurable bus system. In this embodiment, further
programmability is provided at the I/O ports of the system using
gateway interface logic. In particular, the programmable gateway
logic (e.g., 830) is located between the core bus system of lines
(e.g., elements 810, 815, 820) and the I/O (e.g., 825). In the
present embodiment a logic cluster as illustrated in FIG. 4a is
used; however, as noted above, it is contemplated that other forms
of logic can be utilized. In addition, this embodiment includes a
peripheral bus system of lines 840, which functions is a manner
similar to the core bus system of lines, providing a programmable
bus system for transferring information. Preferably, each of the
programmable connections of the bus system (e.g., 846, 847) are
bi-directional, three-statable connections.
[0050] Further enhancements and interconnect flexibility is
achieved by providing programmable connections from the core bus
(e.g., 820) direct to the peripheral bus 840 and from the megacell
(e.g., 845) direct to the peripheral bus 840. For example,
programmable connection 822 selectively enables the bus element 820
to be connected to peripheral bus 840. Similarly, programmable
element 824 selectively connects megacell 845 directly to
peripheral bus 840. Such flexibility is advantageous when speed is
a consideration. For example, it may be desirable to directly
connect externally received control input data to the megacell.
[0051] The invention has been described in conjunction with the
preferred embodiment. It is evident that numerous alternatives,
modifications, variations and uses will be apparent to those
skilled in the art in light of the foregoing description.
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