Abstract:
The present invention provides for reducing power across the entirety of a processor in a series of incremental steps. The clocking power requirements of a processor are evaluated through a power analysis and pre-programmed into a power train generator. A state machine control ramp logic comprising pre-programmed states resets a delay counter and issues state instructions to a pulse train generator. A pulse train generator outputs constant pulse trains and variable pulse trains that mask the original clocking power frequency. The pulse trains are distributed through a timed clock control distribution network to local clock buffers. The conditioned pulse trains step up or step down the clocking power, to the entirety of the processor, resulting in a smoothing of the clocking power switching. The smoothing of the clocking power reduces electrical spikes, surges and capacitance within the processor.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates generally to the field of computer systems and, more particularly, to the reduction of clocking power consumption in a microprocessor.  
         BACKGROUND  
         [0002]    Power consumption is one of the biggest challenges in high performance microprocessor design. The rapid increase in the complexity and speed of each new generation of processors is outpacing the benefits of voltage reduction and feature size architecture. Designers are continuously challenged to come up with innovative ways to reduce power, while trying to meet all the other constraints of the overall design.  
           [0003]    The push towards increasing levels of performance has required an increase in both frequencies and complexities. There are industry-wide concerns that power consumption may eventually set a finite limit on superscalar digital design.  
           [0004]    There are two challenges for power reduction in high performance general purpose processors. First, the instruction-set and system architectures must be designed for a heterogeneous marketplace. This necessarily restricts the search applicable for low-power solutions. Second, it is necessary that the proposed solutions remain robust and scale gracefully across multiple technology generations. Finally, while significant power savings are required, they must be had at little or no loss of performance.  
           [0005]    The operational costs of high frequency processors are not limited to fixed computing environments. Portable devices from laptops to DVD players are increasingly reliant on high demand processors, with a resultant power requirement. In practical applications, however, processors and associated co-processors and logic devices are seldom taxed by full clocking power demands.  
           [0006]    Typically, the clock is the largest user of power within a processing unit. Conventional processor power saving technologies generally focus on reducing power to the clock using clock gating. Clock gating is a well-known technique to reduce clocking power. Because individual circuit usage varies within and across applications, not all the circuits are used all the time, giving rise to power reduction opportunities. By ANDing the clock with a gate-control signal, clock gating essentially disables the clock to a circuit whenever the circuit is not used, avoiding power dissipation due to unnecessary charging and discharging of the unused circuits. Specifically, clock gating targets the clock power consumed in pipeline latches and dynamic CMOS logic circuits that can be used for speed and area advantages over static logic.  
           [0007]    Effective clock gating, however, requires a methodology that determines which circuits are gated, at what time, and for what duration. Clock gating schemes that either result in frequent toggling of the clock gated circuit between enabled and disabled states, or apply clock gating to such small blocks that the clock gating control circuitry is almost as large as the block itself, incur large overhead.  
           [0008]    However, clock gating cannot be used indiscriminately. One large problem is that the disabled block may not power up in time, or that the modified clocks may generate mistimed signals known as skew. This requires strict timing constraints on the enabling signals plus a verification of the timing circuit. Skewing is the apparent or actual variance of the applied clock signal from the original reference clock. Generally, all processors contain at least one reference clock that is split into a plurality of slave clocks, driving other devices or systems. So, the granularity at which clock gating can be applied becomes a tradeoff against overall clock network design and complexity.  
           [0009]    Another concern with clock gating is the impact on current variations when large blocks of logic are switched on and off. A processor may be at peak current levels for some cycles, when few sectors of the processor can be clock gated. However, a processor may rapidly transition to low values of power if a stall of the pipeline cache flush causes a large number of sectors to be powered off.  
           [0010]    Furthermore, the scale of density continues to increase in processor design. This causes two additional problems. First are the additional power requirements for all the additional devices, and second is the extra heat generated. The added density and heat can cause degradation of the clock frequency and signal quality.  
           [0011]    Thus, there is a need for a clock power reduction apparatus that overcomes at least some of the issues associated with conventional clock gating.  
         SUMMARY OF THE INVENTION  
         [0012]    The present invention provides for controlling a processor clock frequency in such a manner as to minimize processor power supply voltage variations while starting and stopping processor clock signals. In order to incrementally change the processor clocking frequency, a power interrupt signal activates a state machine ramp input signal to a state machine ramp control. A delay counter cycles the states and is reset. The state machine selects a pulse train from a generator. The generator multiplexes and masks the clocking power signal, fanning the signal through a timed clock control distribution network. The timed clock control distribution network drives the local clock buffers using the pulse trains. The local clock buffers substantially halt and then restart the processor. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following Detailed Description taken in conjunction with the accompanying drawings, in which:  
         [0014]    [0014]FIG. 1 schematically depicts a conventional system for reducing clock power;  
         [0015]    [0015]FIG. 2 illustrates an apparatus for reduced clocking power with pulse trains;  
         [0016]    [0016]FIG. 2A details a delay counter;  
         [0017]    [0017]FIG. 3 is a diagram illustrating a process of state machine ramp controls;  
         [0018]    [0018]FIG. 4 represents waveforms in power down mode; and  
         [0019]    [0019]FIG. 5 represents waveforms in a power up mode. 
     
    
     DETAILED DESCRIPTION  
       [0020]    In the following discussion, numerous specific details are set forth to provide a thorough understanding of the present invention. However, those skilled in the art will appreciate that the present invention may be practiced without such specific details. In other instances, well-known elements have been illustrated in schematic or block diagram form in order not to obscure the present invention in unnecessary detail. Additionally, for the most part, details concerning network communications, electromagnetic signaling techniques, and the like, have been omitted inasmuch as such details are not considered necessary to obtain a complete understanding of the present invention, and are considered to be within the understanding of persons of ordinary skill in the relevant art.  
         [0021]    In the remainder of this description, a central processing unit (CPU) may be a sole processor of computations in a device. In such a situation, the CPU is typically referred to as an MPU (main processing unit). The processing unit may also be one of many processing units that share the computational load according to some methodology or algorithm developed for a given computational device. All processors process instructions under variable voltage conditions that range from full voltage at design architecture maximum to zero voltage, wherein the processor is processing no instructions. For the remainder of this description, all references to processors shall use the term processor whether the processor is the sole computational element in the device or whether the processor is sharing the computational element with other microprocessors, unless otherwise indicated.  
         [0022]    It is further noted that, unless indicated otherwise, all functions described herein may be performed in either hardware or software, or some combination thereof. In a preferred embodiment, however, the functions are performed by a processor, such as a computer or an electronic data processor, in accordance with code, such as computer program code, software, and/or integrated circuits that are coded to perform such functions, unless indicated otherwise.  
         [0023]    Turning to FIG. 1, disclosed is a conventional clocking power reduction system  100  having an interrupt handler  140 . The interrupt handler  140  is the primary system for prioritizing and caching sent interrupt codes and received control codes. This prioritizing and caching cycle occurs in a full clocking power state or any one of a plurality of less than full clocking power states. The full clocking power or lack of full clocking power, however, does not directly affect the functioning of the cache. In a full clocking power state, all of the system designed power is delivered to the processor  101 . In less than full state, less than full clocking power is delivered to the processor  101 . It can be understood that FIG. 1 is only representative of clocking power control to a single processor. There can be a plurality of processors, each of which has a clock and attendant device.  
         [0024]    Generally, interrupts are processing halts sent to either a software or a hardware device. In FIG. 1, interrupts are sent by the interrupt handler  140  to full power  145  (software or hardware). Dependent on the level of the interrupt signal (determined by a table hierarchy at the system controller  130 ), the full power  145  command is stopped. Typically, interrupts for less than full clocking power are determined by a system controller or other control device. Full clocking power is the maximum processor clocking defined by the system architecture. It can be the default power state, and is exemplified by the full power state  145 .  
         [0025]    The processor clocking power mode is derived from the system controller  130  specifications, the control bus  125  data bandwidth, and the processor design architecture parameters. The sum of these parameters is sent to the interrupt handler  140  from the system controller  130  and processed by computer code.  
         [0026]    Full clocking power is one of the pluralities of options that can be asserted as an output utilizing full power device  145 . The options are generally serial when acting on one processor. In an embodiment containing multiple processors, full clocking power or less-than-full-power can be asserted independently in parallel. Full power device  145  reasserts it is at full clocking power through a handshake or control signal that flows only in one direction from the interrupt handler  140  device towards the full clocking power device  145 . However, the full power device  145  separately returns a control signal to the interrupt handler  140  to allow all interrupts to be in the default ‘off’ position (i.e. no interrupts are active for that portion of the power circuit).  
         [0027]    In FIG. 1, those of ordinary skill in the art understand that a distinction is made between full clocking power, doze and nap states on one side of the clocking power cycle, and a diversity of sleep states on the other. The primary purpose of separating the circuit is to clearly define when the clock/oscillator  120  combination (which consists of two halves: the clock and the PLL) are affected (sleep states) or not affected (full clocking power and doze or nap states). The selection of the division is dependent on a plurality of processor architecture design elements. It can be modeled and coded in hardware or in software, and any number of reduced power states can be asserted. Generally, the clocking power devices are hardware devices.  
         [0028]    Furthermore, those of ordinary skill in the art understand that the processor unit  101  can be logically and physically divided into segments or sectors for power control purpose. The segments or sectors at the processor  101  contain a plurality of gates, registers and other logic devices in hardware. It is these devices that are switched by interrupt codes. Interrupt codes tell systems, sub-systems and related devices to stop processing their instructions.  
         [0029]    The five power states represented in FIG. 1 illustrate one possible design. The five representative power states are full power  145 , doze  146 , nap  148 , sleep  162 , and deep sleep  164 . The purpose of segmenting the power states is a result of a logic decision to keep the phase lock loop (PLL) synthesizer (the clock), and the oscillator (the device that creates a digital frequency wave) at some combination of on or off. At full clocking power  145 , doze  146  or at nap  148 , the PLL and the clock remain on. At sleep  162 , in the clock/oscillator device  120 , the clock is off and the PLL is on. At deep sleep  164 , both the clock and the PLL are off. A new interrupt from handler  140  is required at wake state  165  for the processor  101  to return to full clocking power.  
         [0030]    The system acknowledgment  147  is typically a handshake device passing the interrupt code along the datapath. FIG. 1 shows the relative hierarchy of the various states. Full power  145  typically occurs before nap  148  which, in turn, typically occurs before deep sleep  164 . The power adjustment can last one clock cycle or more. In other words, the interrupt handler  140  cycles through these various software states after sending a request to the full power  145 , reads back the parameters, and applies the parameters to the processor unit  101 .  
         [0031]    The processor unit  101  is coupled to the clock and synthesizer  120  via a host bus  105 . The host bus  105  is a conduit and termination point for signals passing between the clock  120  and the processor  101 . A control bus  125  and a control bus  135  operate similarly.  
         [0032]    Full power  145  always returns at least one control value to the interrupt handler  140 . The architecture of the interrupt handler stops the interrupts from turning on (which would indicate a less than full clocking power demand on the clock). The interrupt handler  140  executes and passes a signal through the control bus  135  to the system controller  130 . This signal is proceeding uninterrupted through the system until it arrives at the processor  101 , where the processor logic understands that all devices have authority to operate at full design capability. The full clocking power state is statically designed, as are any other intermediate states. In other words, there is only one full clocking power state, there is only one doze state, et cetera. The power states are considered switches, switching only on or off. While full power  145 , for example, can issue a control signal, it is not, in itself, a controller. Controller functions are exclusive the system controller  130  in this section of the system  100 .  
         [0033]    Turning now to FIG. 2, disclosed is a clocking power reduction system  200  with a pulse train generator (PTG)  250 . The system  200  is exemplary of one design of a plurality of reduced power state pathways and configurations possible. Typically, the pathways comprise hardware devices that induce a state of reduced processor operation by a device such as nap  148  (which is invoked to turn off one or more sectors at the processor). These devices are affixed in close proximity to the processor  101  because they need to turn on and off sectors of the processor quickly and precisely. The system  200  can be remote of the processor except for the pathway from the local clock buffer  290 .  
         [0034]    The timed clock control distribution network  270  (TCCDN) receives train pulses via a multiplexer  255  (MUX). The MUX  255  mixes and aligns the pulse trains from the PTG  250 . The purpose of the TCCDN  270  is to fan-out the pulse trains to the local clock buffers  290 , delivering the pulse trains at precisely the same moment to each individual LCB  290 . Without this distribution network  270 , the clocking signal and the pulse trains arrive out of sequence and at random, corrupting the processor data in processor  101 .  
         [0035]    Typically, the primary processor clock  120  is divided into a plurality of clocking power outputs, driving a multitude of devices. The outputs can be turned off severally or jointly by a plurality of hardware interrupts. It is generally understood by those of skill in the art that the system  200  represented here can contain a plurality of parallel circuits driven by these clocking power outputs, and acted on dependently by the clocking power output of clock  120 .  
         [0036]    In a latching system, all clocks drive a variety of processes, such as registers, counters and latches. A timing mechanism launches via the host bus  105  and control bus  125 . The logical value stored within the latches varies from a high state to a low state, a logical ‘1’ or a logical ‘0’. The number of devices operating is dependent on the number of the latches clocking on or off within the processor  101  and the frequency of the signal delivered through the LCB  290 , originating with clock  120 . Additional embodiments of the invention can include a plurality of processors and their attendant clocks, in series or in parallel. The circuits thus described can contain a plurality of less-than-full-power states.  
         [0037]    Initialization of the ‘go to nap’ command is via an instruction from the processor  101 . Through the chain of attached buses and devices, the full power  145  sends a request to the nap  148  through an interrupt issued at interrupt handler  140 . Immediately, full power  145  simultaneously issues a control acknowledgment to the interrupt handler  140 , a ramp down request to one input of the state machine ramp control (SMRC)  260  and sets the nap  148  device. Concurrently, a control signal returns from full power  145  through the buses and devices, ending at the processor  101 , which removes the interrupt request. Full power  145  is then set at idle, waiting for a new interrupt instruction from processor  101 .  
         [0038]    The ‘ramp down request’ interrupts pass to the state machine ramp control (SMRC)  260 . The function of the SMRC  260  is to cycle and reset delay counter  240 .  
         [0039]    Turning briefly to FIG. 2A, disclosed is an 8-bit delay counter  240 . The delay counter  240  consists of a plurality of delays that can be infinite in number. The delay counter contains a programmable logic device for partitioning and sequencing the initial delay and every subsequent delay, based on the passing (logical AND gate) of each preceding delay. Typically, the counter is in reset mode, which is a logical ‘0’ or null mode. To start the counter, the SMRC  260  releases the reset signal that the SMRC  260  held at idle. The counter increments by a value of 1 after each clock cycle. In each 8-bit latch delay is a pre-programmed value derived from the external power analysis of the processor architecture. When the delay counter  240  has reached a value that is one of the values stored in one of the delays (for example, delay 1 or delay 2), the corresponding signal “delay ‘x’ passed” is asserted. The counter continues to count clock cycles until reset is reasserted from the SMRC  260 .  
         [0040]    There is a plurality of delay states possible in the delay counter  240 . These are design elements that describe time increments (by clock cycles or other timing means) from delay 1 to delay 2, from delay 2 to delay 3, and from delay 3 to delay (n) in an infinite number of iterations. Included are delays between the ramp down requests and delays between states (1) through state (n) that are the delay states in the delay counter  240 . There is also a delay between delays (n) passed and delays (n) not passed, with the same infinite timing scheme as for the delay counter  240 . The length of time for the delay can be coded in software or by means of hardware devices.  
         [0041]    Turning again to FIG. 2, disclosed is the output of PTG  250 , which has four discrete states “0”, “⅓”, “⅔” and “1”. These numbers represent different pulse trains. The four power states are only illustrative of one embodiment of the apparatus. There can be any number of pre-programmed pulse trains within the PTG  250  control logic and any number of states from SMRC  260  used to select the discrete pulsed outputs. The pulses thus generated are routed to the timed control distribution network  270  (TCCDN). The TCCDN  270  fans out (i.e., routes the pulse train) to the local clock buffers  290 . The logic of the TCCDN  270  is that of a simple ORed gate.  
         [0042]    Each of the local clock buffers (LCBs)  290  matches to a clocking power entry node (i.e., logic contact points) in the die at processor  101 . Local clock buffers can also reside at any other point utilizing a clock frequency. LCBs are clocking power conditioning devices for duplication, distribution and fan-out of the clock signal and pulse trains. There can be a plurality of LCBs matched to a plurality of processors with one or more pulse trains driving them in series or in parallel. Those versed in the art understand that these devices may be on the same chip or on the same circuit board or on a plurality of circuit boards and chips, and all logically connected.  
         [0043]    The LCB  290  distributes the signals according to the netlists contained within a memory logic device. Netlists are lists or tables of conditions matched to actions, residing in programmable storage in the processor  101 .  
         [0044]    Turning to FIG. 3, disclosed is one embodiment of the state machine delay and pass logic sub-system that drives the delay counter  240  devices and issues the state select signal to the PTG  250 .  
         [0045]    Delay (n) represents the discrete difference of the clock  120  periodicity pre-programmed from the processor  101  clocking power analyses. The counter counts delay (1) at state (1) and waits for delay (2). Delay (2) arrives and is counted by the counter, advances state (1) to state (2), until state (n) is passed and the SMRC returns to idle, as the result of a ‘not ramp down request’.  
         [0046]    At idle, the state machine is in null mode and this state signals the PTG  250  to oscillate constant low waveform ‘0’, which produces a constant clock power of the highest design frequency. As ramp down requests are received, the state machine logic transitions from state to state selecting the pulse trains that are pre-programmed. Generally, the delay counter is asserting or deasserting reset and the pulse train select is changing from ‘1 cycle high 2 cycle low’ to ‘1 cycle low 2 cycle high’. At a selection of ‘1’, the clocking power is essentially stopped, though there is always a low level clocking power to maintain vital processor function, even in the deepest sleep mode.  
         [0047]    If “delay 2 passed” is simultaneously asserted at a first ramp down request, the SMRC  260  transitions into state 3. The delay is a time function programmed into the state machine logic, waiting a specified number of clock cycles, before passing into the next state.  
         [0048]    Within each delay state is a sub-state timing delay that is calculated from the algorithms in the delay counter. These sub-state delays are an intermediate and determinate, time dependent idle to the various states (except for the idle state that is actually a null position with no active state). This means that in each overall state, as in “state 1,” there is a sub-state ‘n’ that functions as a timer until the logic determines that state 1 should pass to state 2 or be rescinded (reset).  
         [0049]    If there is no delay from the delay counter  240  in FIG. 2, the state remains static. That is, no delay is asserted and no pass is asserted; in other words, a null state devoid of active processing. However, as the final delay in the delay cascade is passed through the delay counter  240 , the logic in the SMRC  260  algorithm forwards the request to the PTG  250 , where the correct pulse train to power the processor  101  is selected.  
         [0050]    The pulse train select at generator  250  issues a pulse train when the SMRC  260  has made a selection from a comparison of the passed delays waiting at the delay cache  245  to a constant ‘high’ pulse train. The constant high pulse train always indicates an effective clocking power stop condition. The constant low pulse train always indicates a ‘full clocking power’ to processor  101  condition.  
         [0051]    At any point between constant ‘high’ and constant ‘low’, the PTG  250  can use control logic to select one of the pulse trains. Matching the pulse train at a defined point is required to initiate the smooth transition of changed power states in the processor  101 . This step is a significant advancement over the prior art, where the power changes are simply on-off without a transitional phase. As is understood by those of skill in the art, all of the units thus described may reside on a single integrated circuit chip or on discrete circuit boards, and can embody design elements through hardware or software.  
         [0052]    Referring briefly now to FIG. 4, disclosed is an exemplary display of waveforms indicating that the processor is powering down, smoothly. Waveform ‘A’ indicates a clock at latch, where latch is the logic state flip-flop equivalent of an ‘on-off’, clock cycle. Waveform ‘B’ displays the masking pulse train multiplexed from the PTG  250 , wherein it is seen that the pulses are decrementing at the same time as the clock at latch. Waveform ‘C’ illustrates the smooth reduction in power (i.e., decrease in watts) that is novel in the system  200 .  
         [0053]    Referring briefly now to FIG. 5, disclosed is an exemplary display of waveforms indicating the processor is powering up smoothly from an effectively stopped state. Waveform ‘A’ displays a clock in the process of shifting from the reduced power state and latching additional gates at the processor (i.e., indicating higher frequency required to process instructions). Waveform ‘B’ displays the change in the pulse train that matches the higher frequency. Waveform ‘C’ displays the smooth transition to the full clocking power state that is a feature of the system  200  in FIG. 2.  
         [0054]    It is understood that the present invention can take many forms and embodiments. Accordingly, several variations may be made in the foregoing without departing from the spirit or the scope of the invention. The capabilities outlined herein allow for the possibility of a variety of programming models. This disclosure should not be read as preferring any particular programming model, but is instead directed to the underlying mechanisms on which these programming models can be built.  
         [0055]    Having thus described the present invention by reference to certain of its preferred embodiments, it is noted that the embodiments disclosed are illustrative rather than limiting in nature and that a wide range of variations, modifications, changes, and substitutions are contemplated in the foregoing disclosure and, in some instances, some features of the present invention may be employed without a corresponding use of the other features. Many such variations and modifications may be considered desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.