Classifications

• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K5/00—Manipulating of pulses not covered by one of the other main groups of this subclass
  • H03K5/13—Arrangements having a single output and transforming input signals into pulses delivered at desired time intervals
  • H03K5/131—Digitally controlled
• • H—ELECTRICITY
  • H03—ELECTRONIC CIRCUITRY
  • H03K—PULSE TECHNIQUE
  • H03K5/00—Manipulating of pulses not covered by one of the other main groups of this subclass
  • H03K5/159—Applications of delay lines not covered by the preceding subgroups

Definitions

• This relates in general to integrated circuits, and in particular to a method and system for controlling circuit input-output timing.
• Timing closure The process of modifying an integrated circuit (IC) to meet pre-established timing requirements is referred to as "timing closure.”
• Timing closure can be a challenging task for IC designs, because the timing margins shift with changes to process/environment parameters (such as process corners). Accordingly, an optimal implementation for one process corner can fail to meet the timing requirements at another process corner. Numerous place and route and/or other design process iterations may be required to produce a design that meets the pre-established timing requirements (such as setup and hold times) for the IC across process corners. Accordingly, timing closure can result in an objectionable increase in the time and cost associated with designing an IC.
• an integrated circuit includes input/output (I/O) terminals through which signals pass into or out of the IC.
• the IC includes an I/O timing module configured to add propagation delay to signals passing between the I/O terminals and I/O subsystems of the IC.
• the I/O timing module includes delay elements associated with each of the I/O terminals, a control register associated with each of the I/O terminals, a memory, and I/O delay control logic.
• the control register is coupled to each of the delay elements associated with the I/O terminal.
• the memory is encoded with delay information.
• the I/O delay control logic is configured to initialize the propagation delay associated with each of the I/O terminals by selecting which of the delay elements are to be applied to produce the propagation delay based on the delay information stored in the memory.
• FIG. 1 shows a block diagram of an integrated circuit (IC) including input/output (I/O) terminal propagation delay control.
• FIG. 2 shows a block diagram of an I/O timing control module that controls timing at IC I/O terminals.
• FIG. 3 shows a block diagram of a delay calibration controller that measures delays of delay elements applied to control timing at IC I/O terminals.
• FIG. 4 shows a block diagram of a delay controller that sets timing for IC I/O terminals.
• FIG. 5 shows a flow diagram for a method of controlling propagation delay associated with IC I/O terminals.
• a method and system for optimizing timing closure by controlling the propagation delay of signals routed to input/output (I/O) terminals of an integrated circuit (IC) are disclosed herein. Ensuring that circuitry (associated with the I/O terminals) meets predetermined timing requirements is a substantial part of the process of timing closure for the IC. Similar ICs may include similar peripheral devices, but timing closure for I/O signals associated with the peripheral devices may require time consuming iterative static timing analysis using different parameters and adjustment of circuit placement and routing. Furthermore, conventional timing closure processes are strained when multiplexing signals to/from an I/O terminal using I/O pin/signal selection, because additional effort may be required to ensure that each signal meets I/O timing requirements.
• Embodiments of the integrated circuits disclosed herein include I/O timing circuitry that simplifies the process of timing closure for signals routed to/from I/O terminals of an IC. Accordingly, the example embodiments are suitable for reducing cost and time in designing an IC.
• the I/O timing circuitry disclosed herein provides programmable delay to I/O signals, thereby allowing the timing of I/O signals to be controlled without the substantial iterative timing analysis and place and route of conventional ICs.
• Embodiments of the I/O timing circuitry measure the delay provided by delay elements of the I/O timing circuitry under operational conditions, and adaptively apply the delay elements to provide a preprogrammed propagation delay for each I/O signal to meet the pre-established timing requirements of the IC.
• FIG. 1 shows a block diagram of an IC 100 including I/O terminal propagation delay control in accordance with various embodiments.
• the IC 100 includes I/O terminals 106, an I/O timing control module 102, an I/O signal multiplexer 112, and I/O peripherals 104.
• the IC 100 may also include other circuitry and systems that are not shown in FIG. 1 for clarity.
• the I/O terminals 106 are signal transfer structures through which the circuitry of the IC 100 is coupled to circuitry external to the IC 100.
• the I/O terminals 106 may include conductive pins, pads, and other elements.
• the I/O peripherals 104 are subsystems that include various devices that drive signals to or receive signals from one or more of the I/O terminals 106. Examples of devices that may be included in the I/O peripherals include general purpose I/O logic, universal asynchronous/synchronous receive/transmit logic, serial peripheral interface logic, inter-IC (I 2 C) logic, timers, audio ports, network adapters, memory controllers, and video controllers. Signals 108 are routed between the I/O peripherals 104 and the multiplexer 112.
• the multiplexer 112 provides selectable routing of signals between the I/O terminals 112 and the I/O peripherals 104.
• the multiplexer 112 may allow one of sixteen different signals 108 generated by the I/O peripherals 104 to be selectably routed to each I/O terminal 106.
• the multiplexer 112 may allow one of sixteen different I/O terminals 106 to be connected to an input of an I/O peripheral 104. Signals may be selected for routing to/from the I/O terminals 106 during operation of the IC 100.
• the number of signals that can be selectably routed between each of the I/O terminals 106 and outputs of the I/O peripherals, and/or between the I/O terminals 106 and each input of the I/O peripherals 104 may vary in different embodiments of multiplexer 112. Signals 116 are routed between the multiplexer 112 and the I/O timing control module 102.
• the I/O timing control module 102 controls the propagation delay of signals 114 routed to/from the I/O terminals 106 through the I/O timing control module 102 from/to the I/O peripherals 104.
• the I/O timing control module 102 includes a delay controller 110.
• the delay controller 110 determines how a predetermined amount of propagation delay specific to each I/O signal passing through the I/O timing control module 102 is to be generated and applied. By applying an appropriate propagation delay to each I/O signal, the I/O timing control module 102 simplifies timing closure with respect to signals routed to/from the I/O terminals 106.
• the peripheral devices of the I/O peripherals 104 may be included in a "hardened" circuitry component, in conjunction with the I/O timing control module 102 and the multiplexer 112.
• the routing between the peripheral devices and the I/O timing control module 102 is fixed, which simplifies the determination of propagation delays applied by the I/O timing control module 102, and further simplifies the process of timing closure with respect to the signals routed between the I/O terminals 106 and the peripheral devices.
• Some peripheral devices of the I/O peripherals 104 such as complex peripheral devices (including memory controllers and/or video controllers), may be located outside such a hardened component.
• the I/O timing control module 102 also simplifies timing closure with respect to such peripherals.
• FIG. 2 shows a block diagram of the I/O timing control module 102.
• the I/O timing control module 102 includes delay elements 202, a delay interface 204, delay calibration logic 206, the delay controller 110, and delay storage 210.
• the delay storage 210 includes a storage device (such as a non-volatile memory, FLASH storage, or read-only-memory storage).
• Delay values 220 are stored in the delay storage 210.
• the delay values 220 specify the propagation delay to be applied to each I/O signal that can pass through the I/O timing control module 102 to/from an I/O terminal 106.
• the delay values 220 may be determined during design of the IC 100 by analysis of delays across various corners.
• the delay storage 210 may include storage location sufficient to store a number of delay values equivalent to the number of I/O terminals 106 times the number of signals routable to each I/O terminal 106 via the multiplexer 112.
• the delay elements 202 include a set of delay elements or delay lines corresponding to each of the I/O terminals 106.
• the signals 114 associated with the I/O terminals 106, and the signals 116 associated with the multiplexer 112, are connected to the delay elements 202 for insertion of propagation delay.
• the delay elements 202 are selectable and/or programmable to obtain a propagation delay in accordance with each of the delay values stored in the delay storage 210.
• the set of delay elements 202 associated with each I/O terminal 106 includes coarse delay elements 218 and fine delay elements 216. Each of the coarse delay elements 218 provides a substantially longer delay than each of the fine delay elements 216.
• a coarse delay element may provide about 1 nanosecond of delay, and fine delay element may provide less than 100 picoseconds of delay.
• the set of delay elements 202 corresponding to an I/O terminal 106 may include twenty-two (22) coarse delay elements 218 and twenty-two (22) fine delay elements 216. Other embodiments may include a different number of fine and/or coarse delay elements per I/O terminal 106.
• the delay calibration controller 206 measures the delay provided by the coarse delay elements 218 and the delay provided by the fine delay elements 216 during operation of the IC 100.
• the delay controller 110 applies the measured coarse and fine delay values to determine how the delay elements 202 should be applied to achieve a propagation delay value for a given I/O signal, as specified by a delay value 220 retrieved from the delay storage 210. Accordingly, the calibration controller 206 allows the delay controller 110 to account for changes in propagation delay of the delay elements 202 caused by environmental conditions, such as process, temperature, and/or voltage.
• the delay controller 110 controls the delay elements 202 via the delay interface 204.
• the delay interface 204 includes logic (such as a control register corresponding to each I/O terminal 106) that generates control signals for selecting which of the coarse and fine delay elements 218, 216 are to be applied to generate a given signal propagation delay.
• the delay interface 204 may include a control register (coupled to each delay element 202), which provides signals for selecting which of delay elements 202 is to be used for effectuating a needed propagation delay.
• the delay interface 204 also provides an interface to a bus 212 that allows circuitry external to the I/O timing control module 102 to select which of the delay elements 202 are applied to delay an I/O signal, and to communicate with the delay controller 110. Accordingly, via the delay interface 204, external circuitry can override or adjust propagation delay values set by the delay controller 110, and initiate various functions of the I/O timing control module 102.
• the delay controller 110 can change the propagation delay associated with an I/O terminal 106, based on a change in the signal routed to the I/O terminal 106.
• the signals 214 notify the delay controller 110 of changes in the identity, source, and/or destination of signals passing through the I/O timing control module 102. Changes in signal identity, source, and/or destination may be effectuated via the multiplexer 112.
• the delay controller 110 can retrieve a delay value for the new signal from the delay storage 210, determine how the delay elements 202 are to be applied to effectuate the retrieved delay value, and select the appropriate delay elements to effectuate the propagation delay via the delay interface 204.
• the I/O timing control module 102 can vary the propagation delay applied in conjunction with an I/O terminal 106 in association with runtime changes in the identity of the signal routed to the I/O terminal 106.
• FIG. 3 shows a block diagram of the delay calibration controller 206.
• the delay calibration controller 206 measure delays of delay elements 202 applied to control timing at I/O terminals 106.
• the delay calibration controller 206 includes delay counters 302 and 316, reference counters 304 and 318, and delay calculation logic 306.
• the delay calibration controller 206 measures the delay of both coarse and fine delay elements 218, 216.
• the calibration logic 206 selects a predetermined number of coarse delay elements (such as 88 elements), arranged in series.
• the selected set of coarse delay elements 218 is arranged as a ring oscillator, and the oscillation output 308 of the ring oscillator is connected to the delay counter 302.
• the reference counter 304 is incremented by a reference clock signal 310 of known frequency.
• the count outputs of the delay counter 302 and the reference counter 304 are provided the delay calculation logic 306.
• the delay calculation logic 306 can enable counting by the delay counter 302 and the reference counter 304 at a given time (such as a same time) to initiate delay measurement, and disable counting by both counters 302, 304 at a later time (such as when either counter 302, 304 reaches a maximum count value or a predetermined count value).
• the delay calculation logic 306 determines the period of the ring oscillator output 308 and the total delay provided by the serially arranged coarse delay elements 218.
• the delay calculation logic 306 divides the total delay by the number of coarse delay elements 218 in the ring oscillator to determine the delay provided by each individual coarse delay element 218 under operating conditions.
• the delay calculation logic 314 provides the measured delay to the delay controller 110 for use in determining which of the delay elements 202 is to be applied to effectuate a propagation delay.
• the measured coarse delay per element (CDPE) may be calculated as:
• CDPE ⁇ '-
• RefCnt is the final count value of the reference counter 304
• RefClkPeriod is the known period of the reference clock signal 310
• CrsDlyCnt is the final count value of the delay counter 302
• NumCrsElements is the number coarse delay elements in the coarse delay ring oscillator.
• the delay calibration controller 206 measures the delay of fine delay elements 216 in a manner similar to that described for the coarse delay elements 218.
• a number of fine delay elements 216 that is substantially larger than number of coarse delay elements 218 applied in coarse element calibration may be used.
• two-hundred sixty-four (264) fine delay elements may be sequentially arranged to form a ring oscillator generating oscillation signal 320.
• the reference counter 318 and the delay counter 316 are incremented by reference clock 310 and fine delay ring oscillator output clock 320 respectively, until halted by the delay calculation logic 306.
• the final count values of the counters 316, 318 are used for computing the measured fine delay per element (FDPE) as:
• RefCnt is the final count value of the reference counter 318
• RefClkPeriod is the period of the reference clock signal 310
• FineDlyCnt is the final count value of the delay counter 316
• NumFineElements is the number fine delay elements in the fine delay ring oscillator.
• the delay calibration logic 206 may be triggered to measure the delays provided by the elements 216, 218 at device initialization (such as power on reset time). In some embodiments of the I/O timing control module 102, the delay calibration logic 206 may be triggered via the signals 214 to initiate delay measurement. For example, execution of software instructions may trigger recalibration based on an identified change in operating conditions, such as voltage or temperature.
• FIG. 4 shows a block diagram of the delay controller 110.
• the delay controller 110 includes delay adjustment logic 402 that determines which of the set of delay elements 202 corresponding to an I/O terminal 106 to apply to an I/O signal to provide a propagation delay specified by a delay value 220 retrieved from delay storage 210.
• the delay adjustment logic 402 applies the measured delays 314 provided by the delay calibration controller 206, and predicted/expected delay values 404, which may be delay values predicted by design for the coarse and fine delay elements 218, 216 to determine which delay elements 202 should be applied to generate the propagation delay specified by the delay value 220.
• Embodiments of the I/O timing control module 102 overcome this difficulty by specifying propagation delay in two parts, which are: process invariant (agnostic) delay and process variant (gnostic) delay.
• the delay value 220 retrieved from delay storage 210 includes a process agnostic delay value 406 and a process gnostic delay value 412 that conjunctively specify the propagation delay for a corresponding I/O signal I/O terminal combination.
• the process gnostic delay value 412 specifies a portion of the delay value 220 that scales from max corner to min corner of the IC 100, in the same manner as other circuitry of the IC 100.
• the process gnostic delay value 412 includes a coarse delay value 414 and a fine delay value 416.
• the coarse delay value 414 and fine delay value 416 may respectively specify a number coarse delay elements 218 and a number of fine delay elements 216.
• the process agnostic delay value 406 specifies a portion of the delay value 220 that remains the same across corners of the IC 100, such as delay that is fixed with respect to process and operating conditions.
• the process agnostic delay value 406 also includes a coarse delay value 408 and a fine delay value 410.
• the coarse delay value 408 and fine delay value 410 may respectively specify a number coarse delay elements 218 and a number of fine delay elements 216.
• the delay specified by values 408, 410 is process invariant, and consequently does not change with operational conditions.
• the delay controller 110 may compute the total coarse delay (CrsDty) to be applied to a given I/O terminal for a given I/O signal as:
• ACrsDty is a number of process agnostic coarse delay elements (e.g. coarse value 408); PredCrsDty is predicted or expected delay (404) of a coarse delay element; GCrsDty is a number of gnostic coarse delay elements (e.g. coarse value 414); and CDPE is measured delay (314) per coarse delay element.
• the delay adjustment logic 402 determines the number of coarse delay elements 218 to apply as
• CrsElements CrsDty / CDPE .
• the delay adjustment logic 402 computes the total fine delay as:
• FineDty AFineDty * PredFineDty + GFineDty * FDPE
• AFineDty is a number of process agnostic fine delay elements (e.g. fine value 410); PredFineDty is predicted or expected delay (404) of a fine delay element; GFineDty is a number of process gnostic fine delay elements (e.g. fine value 416); and FDPE is measured delay (314) per fine delay element.
• the delay adjustment logic 402 computes the number of fine delay elements 218 to apply in conjunction with CrsElements as:
• FineElements FineDty / FDPE .
• FIG. 5 shows a flow diagram for a method of controlling propagation delay associated with IC I/O terminals 106 in accordance with various embodiments.
• the IC 100 is initialized.
• the IC 100 may be performing operations associated with a power on reset.
• the delay calibration controller 206 measures the delays of the coarse delay elements 218 and the fine delay elements 216 under operating conditions during the initialization of the IC.
• the delay controller 110 accesses the delay storage 210 and retrieves from the delay storage 210 delay values 220.
• the delay values 220 specify the propagation delay to be applied to signal routing for each of the I/O terminals 106.
• Each of the delay values 220 specifies, for a signal routed to an I/O terminal 106, process invariant and process variant portions of the propagation delay for both coarse delay elements 218 and fine delay elements 216.
• the delay controller 110 computes the total coarse delay and the total fine delay to be applied to each signal routed to an I/O terminal 106.
• the total coarse delay is the sum of the coarse process invariant delay and the coarse process variant delay computed for the signal.
• the total fine delay is the sum of the fine process invariant delay and the fine process variant delay computed for the signal.
• the process invariant delays are computed as a product of a nominal or planned coarse/fine delay element delay value and the number of coarse/fine delay elements specified in the coarse/fine process invariant portion of the delay value 220.
• the process variant delays are computed as a product of a measured coarse/fine delay element delay value and the number of coarse/fine delay elements specified in the coarse/fine process variant portion of the delay value 220.
• the delay controller 110 selects which of the coarse delay elements 218 and which of the fine delay elements 216 are to be applied to provide the propagation delay specified by the delay value 220 for routing to an I/O terminal 106.
• the delay controller 110 may identify a number of coarse delay elements 218 to be applied based on the computed total coarse delay and the measured delay of a coarse delay element 218.
• the delay controller 110 may identify a number of fine delay elements 216 to be applied based on the computed total fine delay and the measured delay of a fine delay element 216.
• the delay controller 110 writes information specifying the number of coarse delay elements 218 and the number of fine delay elements 216 to be applied to a control register that provides selection signals to the delay elements 202 corresponding to the I/O terminal 106. For example, one selection signal may be provided to each delay element 202.
• the delay controller 110 receives an indication of a change in signal routing to an I/O terminal 510.
• the signal routed to the I/O terminal 106 may be changed via the multiplexer 112.
• the indication may result from assertion of a signal 214 by circuitry external to the I/O timing control module 102.
• the delay controller 110 retrieves, from the delay storage 210, a delay value 220 corresponding to the new signal.
• the delay controller 110 computes delays for the delay value 220 as described for block 506, and selects delay elements to implement the delay as described for block 508.
• the delay calibration controller 206 is triggered to measure the delays of the coarse delay elements 218 and the fine delay elements 216.
• the triggering may result from assertion of a signal 214 by circuitry external to the I/O timing control module 102.
• the delay calibration controller 206 measures the delays of the coarse delay elements 218 and the fine delay elements 216 as described for block 502.
• the delay controller 110 is triggered to retrieve delay values 220 from the delay storage 210 and update the propagation delays implemented for I/O terminals 106.
• the triggering may result from assertion of a signal 214 by circuitry external to the I/O timing control module 102.
• the delay controller 110 performs the operations described for blocks 504-508.
• a method includes routing signals passing to or from I/O terminals of an IC through an I/O timing module of the IC. Propagation delay is added to the signals in the I/O timing module. Delay elements of the I/O timing module are selected, by the I/O timing module, to apply to each signal and provide the propagation delay based on an identity of the signal and delay information stored in the I/O timing module for the signal.
• an IC includes I/O terminals and an I/O timing module.
• the I/O terminals are configured to pass signals into or out of the IC.
• the I/O timing module is configured to add propagation delay to the signals, and includes arrays of delay elements, propagation delay value storage, a calibration controller, and a delay controller.
• One of the arrays of delay elements corresponds to each of the I/O terminals.
• the propagation delay value storage stores a propagation delay value for each of the signals.
• the calibration controller is configured to measure the propagation delay provided by the delay elements.
• the delay controller is configured to select, for each of the signals, based on the measured propagation delay of the delay elements, which of the delay elements to apply to provide the propagation delay specified by the propagation delay value.

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• Physics & Mathematics (AREA)
• Nonlinear Science (AREA)
• Pulse Circuits (AREA)
• Information Transfer Systems (AREA)
• Semiconductor Integrated Circuits (AREA)
• Design And Manufacture Of Integrated Circuits (AREA)
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• 2013
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