DYNAMICALLY RECONFIGURABLE ARRAY LOGIC

Abstract: A dynamically reconfigurable array logic (DRAL) (l0) is capable of in-system logical reconfiguration in real time and comprises a RAM programmable logic array of bits (l2), each bit comprising a fuse connection between logic elements. I/O means (l4) are coupled to the RAM programmable logic array (l2) for logical selection of registered output. A first register (l6) is coupled for receiving data and high-level commands. A sequencer (l8) includes a pair of up/down counters and functions to generate addresses. A timing device (20) controls DMA transfers and issues READ and WRITE strobes. A second register (26) monitors outputs and functions as a comparator, in a first mode, and functions to load outputs during specified time intervals in a second mode.

Description: This invention relates generally to computers and data processing systems including programmable methods or procedures and more particularly to a programmable logic array based on a RAM cell coupled with an intelligent direct memory access (DMA) controller. Conventional programmable logic utilises an array of logic gates which have selectable inputs. For instance, a 20-pin programmable logic device may contain a number of 32-input AND gates. The 32 inputs generally comprise both the true and complement of logic inputs and certain feedback signals from outputs. These AND gates, in turn, feed an array of OR gates or NOR gates. Thus, if one breaks down a desired logic function into the familiar sum-of-products form (MIN TERMS) it may be implemented by selecting only the appropriate inputs to the AND gates and possibly the OR (NOR) gates. In most programmable logic devices the connections between AND and OR (NOR) gates are fixed, sacrificing some programmable logic flexibility, but keeping device complexity at a more reasonable level. Typically, interconnections among logic elements in the array are achieved via a fusible link or non-volatile memory cell (EPROM or EEPROM). Therefore, once a logic function for a device has been decided, it is programmed and designed into a system. At this point, the logic function of the device is fixed. It is either totally incapable of being reprogrammed, or it must be removed from the system to be reprogrammed. EP-A-0 055 348 discloses a dynamically reprogrammable logic array system which includes an AND array and an OR array as discussed above. Commands stored in a load directory specify subarrays within an array for repersonalisation. However, EP-A-0 055 348 does not teach that the array can initiate its own reprogramming based upon its logic state. An article entitled "A User Programmable Reconfigurable Logic Array" appearing in the Proceedings of the IEEE, 1986, Custom Integrated Circuits Conference, Rochester, New York, 12-15th May 1986, pages 233-235 discloses a user programmable logic device in which the known programming by way of fusible links is replaced by a distributed dual port static memory. This device does not have the capability spontaneously to initiate its own reconfiguration based upon the state of the device. Furthermore, the device must be reconfigured in its entirety, whereas with the present invention any portion of the array can be reconfigured individually and at random. The foregoing illustrates limitations known to exist in present devices. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above and this is the objective of the present invention. The present invention is defined in the appended claims and according to one aspect of the invention the objective thereof is accomplished by a dynamically reconfigurable array logic including a RAM programmable logic array comprising an array of bits, each bit comprising a fuse connection between logic elements. Input/Output (I/O) means are coupled for logical selection of registered output. A first register receives data and high level commands. A sequencer generates addresses. A timing device issues read/write (R/W) strobes and a second register monitors outputs in both a first and a second mode. The foregoing and other aspects will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. It is to be expressly understood, however, that the drawings are not intended as a definition of the invention but are for the purpose of illustration only. In the drawing: Figure l is a diagrammatic view illustrating an embodiment of the dynamically reconfigurable array logic of the present invention; Figure 2 is a diagrammatic view illustrating an embodiment of a RAM fuse in terms of standard logic devices; Figure 3 is a diagrammatic view illustrating an embodiment of a typical system utilising the dynamically reconfigurable array logic of Figure l; and Figure 4 is a diagrammatic view illustrating the flow of activity of an associated central processing unit (CPU). A dynamically reconfigurable array logic (DRAL) provides a programmable logic device with the new capability afforded by the present invention; in-system logical reconfiguration in real time. One of the keys to accomplishing this versatility is the use of a RAM cell to dictate a connect/no connect condition at each junction or "fuse" in the device. This programmable logic device is partly autonomous in a system, possessing the ability to download any of a number of logic programmes from non-volatile memory to itself via a DMA controller. However, it is also system-dependent. A CPU (Central Processing Unit) interface allows a host processor to change any of the logical connections in the device simply by writing the information for those connections into a RAM. In addition, the DRAL may accept some simple high level commands, such: as "download new logic pattern into X number of 'fuses' starting at address y in a non-volatile memory". Collectively, these capabilities allow the DRAL to perform many functions within a system which are not afforded by out-of-system programmable logic devices. Applications for such a real-time reconfigurable logic device include multiprocessing, memory management, fault tolerant hardware, artificial intelligence, time-shared logic, and even emulation of existing programmable logic devices for circuit development. The DRAL allows the system into which it is placed to adapt in real time, making a single set of hardware much more versatile. It is hardware which is completely alterable by software. A DRAL block diagram is designated l0 in Figure l. A RAM Programmable Logic Array l2 consists of an array of approximately 2000 RAM bits, each of which is equivalent to a fuse connection between logic elements. One possible implementation of a RAM fuse is shown in Figure 2. This is merely a functional representation of a fuse in terms of standard logic devices. A real implementation of any complexity would utilise advantage of VLSI architecture to minimise the circuitry needed for each fuse. The connections are made by writing a l at input ll to a particular fuse 2l including a bi-stable device l3 and a tri-state inverter l5, allowing the output of a NAND gate l7 to reflect the opposite polarity of a logic input 0 at l9 (this must be taken into account when generating a logic programme). Connections are inhibited by writing logic input 0 to the fuse 2l, forcing the output of the NAND gate l7 high. Thus, logic input 0 to fuse the 2l has no controlling action over the logic output of the product term's AND gate 23. It is possible at the cost of a greater circuit complexity, to select the interconnections between AND and OR (NOR) gates using a second array of RAM fuses, making the DRAL a complete programmable logic array (PLA). It should be noted that the primary difference between a DRAL RAM cell l2 and a conventional RAM cell is that the output of a conventional RAM cell is only available when that cell is addressed. A plurality of I/O macrocells l4 allows logical selection of registered output, combinatorial output, or bidirectional operation. These configurations are determined by multiplexers and are also RAM programmable. Such I/O configurations are prevalent in existing programmable logic devices. Data is passed between DRAL l0 and other devices via an 8-bit bus. Within DRAL l0, data may be passed to a command register l6, to which a host CPU, not shown, issues high-level commands, the RAM programmable logic array l2, in which "fuses" are organised in bytes, and an address sequencer l8 comprising a pair of up/down counters which generate addresses for autonomous DMA transfers between DRAL l0 and its logical memory. A timing controller 20 issues appropriate R/W strobes 22 to a local memory to orchestrate DMA transfers. The R/W strobes 22, as well as an Address Bus 24, are bidirectional, allowing a processor to control them during transactions between itself and DRAL l0. An interrupt/test register 26 functions in two ways, during both of which it monitors the outputs of DRAL l0. In one mode, a host CPU writes an interrupt code, starting interrupt addresses, and an address offset to DRAL l0. The interrupt/test register 26 then functions as a comparator, watching for a match between the interrupt code and the state of the DRAL l0 outputs. If a match occurs, the starting interrupt addresses are loaded into the two counters of address sequencer l8, and DRAL l0 commences downloading a new logic programme from starting interrupt addresses to final interrupt addresses using direct memory access. This feature allows DRAL l0 automatically to change its own logic based on an output condition anticipated by the host processor. In a second mode, the interrupt/test register 26 loads DRAL l0 outputs during each specified time interval and writes the values to its own off-board RAM. This trace function allows the CPU to read that RAM at a later date and evaluate/verify correct operation of DRAL l0. Interrupt/test register 26 also has the ability to transmit data serially for testing purposes. Figure 3 depicts a typical system configuration utilising DRAL l0. In this configuration DRAL l0 is isolated from the main processor bus by tri-state latches 28 and transceivers 30. A bank of non-volatile programme memory 32 containing logic fuse maps for DRAL l0 must lie on its local address and data buses, 36, 38, respectively. An optional bank of RAM 34 may also lie on the local bus if trace data from DRAL l0 needs to be recorded. Address decoding 37 must also be provided to allow the CPU to select DRAL l0, which appears as an I/O device to any microprocessor. Upon power-up, DRAL l0 disables (tri-state) its system inputs and outputs and automatically downloads the default logic map from the non-volatile memory 32 into its own fuse map. With a logic configuration similar to a 20-pin PLA, this will typically consist of 2056 fuses, plus 32 fuses to configure input latches 39 and I/O macrocells l4 (see also Figure l). With an 8-bit data bus, 260 data transfers must take place to constitute a complete fuse map download. When the fuse map download is complete, DRAL l0 enables its system inputs and outputs, and the device commences with its operation in the system. If, at any time during operation, the logic programme needs to be changed, the host CPU may do so in two ways; in either case the processor must write to command register l6 within DRAL l0. Typically the system decoding issues a bus request to DRAL l0, and the DRAL l0 bus acknowledge signal then enables the latch 28 and the transceiver 30 connected to the access RAM 34 or PROM 32 on the DRAL l0 local bus, or the command register l6 within DRAL l0 itself. Five command types are supported as shown in Figure 4: l) read or write eight fuses in the RAM array at the next address specified, 2) reload X fuse words (8 bits) starting at RAM array address Y2, and non-volatile memory address Yl, 3) reinitialise DRAL l0 starting at non-volatile memory address Y, 4) trace X output bytes at timing interval Z and write them to RAM starting at address Y, 5) monitor outputs for interrupt state A and reload X fuse words starting at RAM array address Y2 and non-volatile memory address Yl if the interrupt occurs. Upon receiving the first type of command, a control unit 40 (Figure l) configures DRAL l0 to accept a host processor address for the RAM Programmable Logic Array l2. On the processors's next access to DRAL l0, it must either read or write logic fuses in the array, using its data strobe and R/W lines to control the write and read lines on DRAL l0. During a write to any of the fuses in the device, DRAL l0 isolates its inputs and outputs to the system to avoid metastable logic conditions on its outputs. The system signals are re-enabled automatically after a write cycle has been completed. A read cycle to the DRAL l0 fuse map may be completed without interference with the DRAL l0 system inputs and outputs. After receiving a command of the second or third type, the control unit 40 configures address sequencer l8 to receive data from the processor for the starting PROM 32 address and, in the case of the second type of command, also for starting RAM array address and address offset. These pieces of information are passed to DRAL l0 with successive write cycles from the CPU. After all address information has been received, DRAL l0 initiates DMA transfers from the non-volatile memory 32 to the RAM Programmable Logic Array l2. During all such DMA transfers, DRAL l0 disables its system inputs and outputs and activates a discrete BUSY signal, which may be used to notify the system that DRAL l0 is temporarily disabled. Once all DMA download is complete, DRAL l0 continues to operate in the system using its new logic fuse map. The fourth type of command must be accompanied by a byte describing at what interval to sample the outputs, and data words describing the number of traces and the starting trace address in RAM 34. Again, this information must accompany the command in the form of successive write cycles from the CPU. During any trace activity, DRAL l0 signals the system that its bus is busy. After the trace operation has been completed, the host processor may read the trace data from RAM 34 on the DRAL l0 local bus. All data transfers between the system processor(s) and DRAL l0 are coordinated with the BUS REQUEST, BUS ACKNOWLEDGE, CHIP SELECT, READ, and WRITE signals. A BUS REQUEST need only be issued by the CPU prior to each command. A BUS ACKNOWLEDGE from DRAL l0 notifies the CPU that it is awaiting a CHIP SELECT, ADDRESS, and READ and WRITE to complete the access cycle. If a command is written to DRAL l0, it continues to acknowledge the bus until all data which must accompany that command is written. If the BUS REQUEST is used to access the DRAL l0, local RAM 34, or PROM 32, then the BUS ACKNOWLEDGE expires immediately after the BUS REQUEST is removed. Figure 4 illustrates the flow of CPU activity which must take place during its access to DRAL l0 or to components which lie on its local bus, including the specification of data for the four command types. The address space of DRAL l0 should be at least 2 K bytes (ll address lines), which affords it the capability autonomously to download up to seven complete logic programmes. Since it is also possible for DRAL l0 to mix and match portions of logic programmes in the non-volatile memory 32, the possible combinations of logic from 2K bytes of PROM 32 is virtually limitless. The foregoing has described a programmable logic array based on a ram cell, rather than a fusible link or EPROM cell, coupled with an intelligent DMA controller. The logic implemented in the device is reprogrammable in real time within the system. A CPU may change an individual logic term, or the DMA controller may download a logic programme from the non-volatile memory. This creates a block of adaptive logic which can serve several purposes in a system based on need signallled by a CPU. This invention allows its logic to take on many functions simply by rapidly downloading a new fuse pattern specifying logical interconnection. It may act as programmable decoder or even an adaptive state machine, specifying a change in its own logic based on transitions to certain states. As a result, a single block of logic can perform multiple, time-shared functions in a system. This device could also act as a sophisticated controller for adaptive signal processing or adaptive control systems. Ideally, it would be fabricated on a single chip and would be fast enough to completely reload itself in less than 200 microseconds.

Claims: A dynamically reconfigurable array logic characterised in that it comprises: a RAM programmable logic array (12) comprising an array of bits, each bit comprising a fuse connection between logic elements; I/O means (14) coupled to the RAM programmable logic array (12) for logical selection of a registered output; first register means (16) coupled to the RAM programmable logic array (12) for receiving data and high level commands; sequencer means (18) coupled to the RAM programmable logic array (12) for generating addresses; timing means (20) coupled to the RAM programmable logic array (12) for issuing READ and WRITE strobes; and second register means (26) coupled to the RAM programmable logic array (12) for monitoring outputs in both a first mode and second mode. Array logic according to claim 1, characterised in that the sequencer means includes a pair of up/down counters (18). Array logic of claim 2, characterised in that during the first mode, the second register means (26) loads addresses into the counters of the sequencer means (18). Array logic according to claim 2 or 3, characterised in that the second register means (26) functions as a comparator in the first mode and to load outputs during specified time intervals in the second mode. Array logic according to claim 4, characterised in that the second register means (26) is responsive in the first mode to control signals from the first register means (16) and to output signals from the I/O means (14) and is operable to compare said control and output signals and provide portions of the control signal to the RAM programmable logic array (12) when the compared signals are equal, thereby to reconfigure the logic array. Array logic according to claim 5, characterised in that it additionally comprises bus means for coupling control signals between the RAM programmable logic array (12), the first register means (16) and the second register means (26). Array logic according to any of the preceding claims, characterised in that the timing means (20) controls DMA transfers. Array logic according to any of the preceding claims, characterised in that the second register means includes an interrupt/test register (26). Array logic according to any of the preceding claims, characterised in that the RAM programmable logic array (12) is coupled to tri-state latches (28) and transceivers (30). Array logic according to claim 9, characterised in that the RAM programmable logic array (12) is coupled to a PROM (32) and a RAM (34) via a local data bus (38) and local address bus (36).

Inventors: HENRY, MATHEW W.
Applicants: HONEYWELL INC.
Application year: 1987
Main classification: H03K19
IPC codes: G06F9, H03K19