Debug interface for an event timer apparatus

[00002] 1. Field of the Invention

[00003] The invention generally relates to the testing and debugging of the operation of an event timer, and more particularly, to an on-chip system and method for monitoring and controlling the event timer's operation for validation purpose.

[00004] 2. Description of the Related Art

[00005] Event timers which are used in personal computers are intended for use by the operating system software. Different kinds of applications may be controlled by event timers, e.g. the synchronization of real time digital audio and video streams, the scheduling of threads, tasks, processes etc. using a fixed rate (periodic) interrupt generation, the scheduling of run time threads, tasks, processes etc. associated with a variable rate (aperiodic) interrupt generation, and applications on multi-processor platforms using such timers as a “platform timer”.

[00006] Recently, an event timer (“multimedia timer”—MMT) has been developed which is designated to replace previous legacy timers in a personal computer (in particular the 8254 Programmable Interval Timer, the Real Time Clock, the APIC timer and the ACPI timer).

[00007] The event timer's architecture defines a set of timers that can be used by the operating system. The timers are defined such that the operating system may be able to assign specific timers to be used directly by specific applications. Each timer can be configured to cause a separate interrupt. An interrupt may be either a (sub-millisecond) periodic interrupt, which is of much finer granularity than provided by previously used timers, or aperiodic timer interrupts.

[00008] The event timer enables higher clock resolution for improving multimedia support and enables aperiodic interrupts, improving both multimedia support and overall system performance.

[00009] The timers are implemented as a single up-counter with a set of comparators. The basic timer configuration is illustrated in FIG. 1. A clock generator 1 provides a clock signal of a fixed frequency to an up-counter 2. The count result of the up-counter increases monotonically. Each timer includes a match register 3 and a comparator 4. The timer can generate an interrupt when the pre-programmed count value in match register 3 equals the count value of the free-running up-counter 2. The interrupt is forwarded to an interrupt routing logic 5 forwarding the interrupt to appropriate parts of the microprocessor. In particular, the registers associated with the timers may be mapped to memory space allowing the CPU to directly address each of the registers.

[00010] A more detailed hardware block diagram of the event timer configuration is shown in FIG. 2. The configuration comprises a single up-counter 2 with a plurality of comparators 10, 11, 12. The count value of the single up-counter 2 increases in accordance with a clock signal received from an (external) clock generator 1. The clock frequency is preferably 14.318 MHz, and the up-counter's count value has a width of 32 bit. In accordance with the recommended hardware implementation, the clock's frequency should not be below 10 MHz. As shown in FIG. 2, the minimum recommended hardware implementation comprises three individual timers including a match register 7, 8, 9 and a comparator 10, 11, 12. Each of the timers can individually generate an interrupt when the pre-set value in its match register 7, 8, 9 equals the count value of the single up-counter 2. Each of the match registers 7, 8, 9 and the comparators 10, 11, 12 should have a width of either 32 bit (minimum) or 64 bit.

[00011] In addition, some of the timers may be enabled to generate a periodic interrupt. For this purpose such timers comprise an additional period register 13 and an adder in order to increase the match register's count value periodically.

[00012] Further, the individual registers of the event timer may be connected to a data bus allowing to read or write the individual register values.

[00013] It has become very difficult to diagnose failures in, and to measure the performance of state of the art event timers. This is because modern event timers run at very high clock speed, too fast for validation software to react in real time. Moreover, visibility of event timers inner states has become increasingly limited due to the complexity of on chip architectures and due to practical constraints on the number of externally available contact pads that can be provided on a chip package.

[00014] A need therefore exists for an event timer apparatus, for a debug interface for an event timer apparatus and a method for enabling event timer designers to debug state of the art event timers and systems more easily. More specifically, there exists a need for an on-chip system, an on-chip interface and a method for validating the event timer's functionality.

[00015] It is therefore a primary object of this invention to provide an event timer apparatus, a debug interface and a method which allow an easier validation of the event timer's functionality.

[00016] Another primary object of this invention is to provide an event timer apparatus, an on-chip debug interface and a method which allows hardware validation without fulfilling real time requirements.

[00017] An improved event timer apparatus, debug interface and method are provided that enable the use of non-real time validation software.

[00018] In one embodiment, an event timer apparatus is provided, comprising a hardware timer. The hardware timer includes at least an up-counter, a match register and a comparator. The up-counter counts clocks of a clock signal. The match register stores a programmable count value. The comparator monitors whether the up-counter's count value matches the count value of the match register. The event timer apparatus further comprises a debug interface. The debug interface includes an enable control unit for enabling the up-counter's operation based on a pre-defined relationship between a state of an enable signal supplied to said up-counter and an internal state of the hardware timer.

[00019] In another embodiment, a debug interface for use with an event timer apparatus is provided. The event timer apparatus comprises a hardware timer which includes at least an up-counter, a match register, and a comparator. The up-counter counts clocks of a clock signal. The match register stores a programmable count value. The comparator monitors whether the up-counter's count value matches the count value of the match register. The debug interface comprises an enable control unit for enabling the up-counter's operation based on a pre-defined relationship between a state of an enable signal for that up-counter and an internal state of the hardware timer.

[00020] In still another embodiment, a method for debugging the operation of an event timer is provided. Said event timer comprises a hardware timer including at least an up-counter, a match register, and a comparator. The up-counter counts clocks of a clock signal. The match register stores a programmable count value. The comparator monitors whether the up-counter's count value matches the count value of the match register. The method monitors an internal state of that event timer and generates a hold signal to stop the operation of the up-counter if a monitored internal state matches a pre-defined condition.

[00021] Further embodiments are the subject-matter of dependent claims.

[00031] The illustrative embodiments of the present invention will be described with reference to the Figure drawings.

[00032] Referring to the drawings and in particular to FIG. 3, which illustrates a debug interface connected to an event timer. The configuration of FIG. 3 shows those components of an event timer, in particular the event timer (MMT) 6 as described with reference to FIG. 2, which interact with a debug interface as described herein. The debug interface 16 of the present invention monitors internal states of the event timer 6. The debug interface 16 generates an enable signal 18 for controlling the operation of the up-counter 2 in the event timer 6 based on a pre-defined relationship between the monitored internal state of the event timer and the enable signal 18. Preferably, the internal states of the event timer 6, e.g. interrupts generated by the event timer, are stored in a register 17 which may be read by the debug interface 16.

[00033] Due to the functionality built into the debug interface 16, interrupt events will be triggered upon the occurrence of a programmed internal event, e.g. an interrupt generated by a comparator of the event timer, without having to first transmit data off-chip. The event to be monitored may be programmed externally by setting a particular register in the debug interface, details of which will be described below.

[00034] In the event timer apparatus 6, the data registers for latching events are implemented “on-chip”. It is difficult to debug both, the event timer and software used therewith. By the use of the integral debug interface 16, the variety of internal signals which only exists internally on a chip and does not propagate to the top of the chip, may be designed to receive signals from the event timer and trigger the event timer based on a pre-programmed relationship. Being programmable, the debug interface 16 comprises at least a programmable debug register for holding parameters controlling the up-counter's operation, i.e. a start and stop the up-counting procedure.

[00035] An exemplary flow chart illustrating a debug operation is shown in FIG. 4. After the parameters for the selection of internal state has been externally set (step S1) the debug operation enters a monitoring state (step S2). If the pre-programmed internal state is detected (step S3) the up-counter's operation is stopped (step S4). Such a debug procedure enables a user to intentionally stop the timer operation depending on the occurrence of a pre-programmed event. Thus, the event timer's and the software's functionality may be step-wisely validated. Such a debug operation enables an efficient validation without a need for transmit data off-chip. The debug interface needs only to be programmed by setting the debug register.

[00036] In one particular embodiment, the debug interface allows to adaptively set the event timer's processing speed. In particular, the processing speed for approaching particular internal events may be reduced in order to cope with the non-real time software capabilities. The configuration of such a particular embodiment is illustrated in FIG. 5. As illustrated therein, the up-counter's clock signal from clock generator 1 is further branched off to the debug interface 16. Based on the received clock signal 20, the debug interface is put into a position to control the up-counter's counting procedure. The particular configuration of such a debug interface will be described in more detail below.

[00037] Turning now to FIG. 6, illustrating a particular implementation of debug interface 16. Debug interface 16 comprises an enable control unit 23, monitoring means 22 and a debug register 21. Upon receiving a pre-programmed event signal from monitoring means 22, the enable control unit 23 generates a stop signal in order to set the up-counter's operation on hold. A particular event of the event timer 6 is monitored by monitoring means 22 which is connected to the debug register 21. Debug register 21 can be programmed to select a particular internal state by setting an “enable stop” register or bit by the user. To monitor the internal state, the monitoring means 22 may be a multiplier multiplying the internal state with the value set in the debug register 21. Alternatively, the monitoring means may be an AND gate or may exclusively OR the internal state with the register's signal. As those skilled in the art will appreciate, the monitoring means may be implemented to the same effect using a variety of means for passing the selected event signals to be monitored.

[00038] As previously stated, the above-described debug interface 16 may be used to reduce the processing speed of the event timer. An exemplary embodiment of such a debug interface is illustrated in FIG. 7. The debug interface 16 is similar to the configuration shown in FIG. 6. Additionally, the debug interface comprises a clock divider 24 connected to the enable control unit and connected to a divider value register 25. The received clock value 20 branched off from the clock signal, provided to the up-counter 2, is received by clock divider 24 in order to reduce the clock's frequency in accordance with the pre-programmed divider value. The new clock 20′ having a reduced clock frequency is applied to the enable control unit 23. Based on the received clock 20′ with the reduced clock frequency, the enable control unit adapts the up-counter's processing speed to the reduced clock frequency by generating appropriate start/stop signals 18. In order to preserve the reduced processing speed of the event timer, the start/stop signal 18 is produced periodically. In this manner, the event timer's operation and the processing of the validation software may be monitored step-wisely in response to the external settings of the debug interface.

[00039] These external settings may be provided in separate debug registers, namely for programming internal states to be monitored in debug register 21 and a clock divider value register 25, or in a common register combining all externally set parameters.

[00040] FIG. 8 illustrates the configuration of an event timer and debug interface, referred to above. As previously stated, the above-described event timer 6 may be an event timer as currently developed for use with personal computers. In a preferred embodiment of the debug interface 16, the event timer 6 is such an event timer. The particular configuration of the event timer shown in FIG. 8 is similar to that described in connection with FIG. 2. The on-chip event timer FIG. 8 differs from that of FIG. 2 by an internal register 17 which allows the debug interface to read the current internal states. Further, the on-chip implementation of the event timer comprises an up-counter 2 the operation of which is controlled by the on-chip debug interface 16, in particular by the enable control unit 23 included in the debug interface. In addition, the clock signal provided to up-counter 2 is branched off to the debug interface.

[00041] The configuration of debug interface 16 shown in FIG. 8 is similar to that illustrated in FIG. 7. The illustrated configuration differs from that of FIG. 7 by a single debug control register 27 storing pre-programmed parameters relating to a divider value for controlling clock divider 24 and enable stop bits for selecting particular internal states to be monitored. In particular, the illustrated configuration monitors a plurality of internal states stored in register 17. Which of the internal states may trigger a stop signal generated by the enable control unit 23 depends on the settings in the debug control user 26. Only those interrupts may trigger a response of the enable control unit 23 which are previously selected by a user in the debug control register 26.

[00042] An important feature of the above described configuration is the ability to generate a stop signal for halting the up-counter's operation without transmitting any internal data off-chip. The debug interface enables a software and event timer validation procedure by simply setting the parameters of the above-identified debug control register.

[00043] External hardware and software may be used to program the aforementioned parameters and conditions, to receive an interrupt match and event data, and to interpret the interrupt match and event data to debug the event timer and software.

[00044] Summarizing, the debug interface enables an external user to monitor internal states of the event timer and to stop the event timer's main counter based on internal conditions. The debug interface supports a successful validation by enabling a stop of the event timer's operation after the current count matches a pre-defined condition, by reducing the input clock for the up-counter to monitor the timer operation by software, and to start the counter for a pre-determined number of cycles. This allows to previously define a number of counting steps to be performed by up-counter 2.

[00045] An important feature of the above-described event timer and debug interface is the ability to enable the testing and debug of the event timer without degrading the operation of other functions of the event timer.

[00046] While the invention has been described with respect to the physical embodiments constructed in accordance therewith, it will be apparent to those skilled in the art that various modifications, variations and improvements of the present invention may be made in light of the above teachings and within the purview of the independent claims without departing from the spirit and the intended scope of the invention. In addition, those areas in which it is believed that those of ordinary skill in the art are familiar, have not been described herein in order to not unnecessarily obscure the invention described herein. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrative embodiments, but only by the scope of the dependent claims.