Semiconductor integrated circuit, interconnect, and computer readable medium storing medium storing control program

A semiconductor integrated circuit includes an adjuster and a controller. The adjuster adjusts transmission and reception of data by temporarily holding the data transmitted and received among a plurality of devices and output location information on the data. The controller controls power consumption of at least one of target devices based on a change amount of the location information.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2010-204505, filed on Sep. 13, 2010, the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a semiconductor integrated circuit, an interconnect and a computer readable medium storing control program.

BACKGROUND

Recently, a demand for reducing power consumption of a semiconductor integrated circuit is increased, more specifically, in the following case.

For example, a plurality of chips is stacked in order to enlarge the semiconductor integrated circuit. In this case, heat between the chips is hardly dissipated. However, if a sufficient radiator such as a heat sink is attached in order to dissipate the heat between the chips, the semiconductor integrated circuit can be thin. Accordingly, reduction of the power consumption (particularly, peak power) of the semiconductor integrated circuit is required when the chips are stacked.

There is well known a technology called Dynamic Voltage and Frequency Scaling (hereinafter referred to as “DVFS”). In the DVFS, a power consumed in operating the semiconductor integrated circuit is reduced by operating the semiconductor integrated circuit at the minimum voltage and frequency.

However, the conventional control circuit (hereinafter referred to as “VFC (Voltage Frequency Controller)”) that realizes the DVFS is individually developed in each application. Therefore, the conventional VFCs does not have versatility and high reusability.

DETAILED DESCRIPTION

In general, according to one embodiment, a semiconductor integrated circuit includes an adjuster and a controller. The adjuster adjusts transmission and reception of data by temporarily holding the data transmitted and received among a plurality of devices and output location information on the data. The controller controls power consumption of at least one of target devices based on a change amount of the location information.

A semiconductor integrated circuit of the embodiment will be explained below.FIG. 1is a block diagram illustrating a configuration of the semiconductor integrated circuit of the embodiment.

Referring toFIG. 1, a semiconductor integrated circuit1includes an interconnect10, an MPU (Micro Processing Unit)21, a DSP (Digital Signal Processor)22, a memory23, an interface24, a peripheral25, and an inputting apparatus26.

The interconnect10is a module that controls data transmission and reception among the MPU21, the DSP22, the memory23, and the peripheral25. The MPU21and the DSP are processors that perform pieces of predetermined processing. The memory23is a module in which pieces of data necessary for processing performed by the MPU21, the DSP22, and the peripheral25are stored. The interface24is a module that controls data transmission and reception among the interconnect10, the peripheral25and inputting apparatus26. The peripheral25is a device that transmits and receives the data among the MPU21, the DSP22, and the memory23. The inputting apparatus26receives inputs of parameters (a first threshold TH1to a fourth threshold TH4and a threshold voltage VTH) necessary for the DVFS and operation modes (a low power consumption mode LP and a high speed mode HS). When the low power consumption mode LP is set, power consumption is prior to an operating speed. When the high speed mode HS is set, the operating speed is prior to the power consumption. Each of the DSP22, the memory23, and the interface24includes a regulator and a clock gear. The interface24can be connected to various devices through a network.

The interconnect of the embodiment will be explained below.FIG. 2is a block diagram illustrating a configuration of the interconnect10ofFIG. 1.

The interconnect10includes an adjuster11, a VFC12, and a monitor13.

The adjuster11is a module that adjusts transmission and reception of data D by temporarily holding the data D transmitted and received among plural devices (the MPU21, DSP22, memory23, and peripheral25ofFIG. 1). The adjuster11receives the data D transmitted from the MPU21, DSP22, memory23, and peripheral25, temporarily holds the received data D, and transmits the held data D to the MPU21, DSP22, memory23, and peripheral25. The adjuster11acts as a slave device when the data D is received and acts as a master device when the data D is transmitted. That is, the MPU21, the DSP22, the memory23, and the peripheral25act as the master device when the adjuster11receives the data D, and the MPU21, the DSP22, the memory23, and the peripheral25act as the slave device when the adjuster11transmits the data D. The adjuster11outputs location information LI on the data D when the data D is held. The location information LI indicates a location of the data D in the adjuster11and changes according to a state of the transmission and reception of the data D. For example, the adjuster11is an FIFO (First In First Out) memory or a memory such as a register map. For example, the location information LI is an index value in the case of the FIFO memory is an address in the case of the memory.

The VFC12is a module that controls power consumption of a target device by performing the DVFS based on the output (the location information LI) of the adjuster11. The VFC12performs the DVFS to generate a voltage control signal VCS and a frequency control signal FCS. Then, the VFC12outputs the generated voltage control signal VCS and frequency control signal FCS to a target device which that becomes a target of the data transmission and reception. The target device is the MPU21, the DSP22, the memory23, and the peripheral25ofFIG. 1. For example, the VFC12generates the voltage control signal VCS and the frequency control signal FCS according to TABLE 1. The VFC12may be provided in any place (for example, an outside of the interconnect10) in the semiconductor integrated circuit1. The VFC12may be implemented by software (for example, the MPU21that executes a control program).

The monitor13is a module that monitors an operating environment of the target device. When the operating environment is abnormal, the monitor13generates an interrupt signal IS and outputs the generated interrupt signal IS to the VFC12. For example, the operating environment is an operating temperature or an operating current of the target device. The monitor13generates the interrupt signal IS when the operating temperature or operating current of the target device is more than a predetermined value.

First Embodiment

A first embodiment will be explained below. In the first embodiment, the DVFS is explained by way of example when the target device is the slave device.

The DVFS of the first embodiment will be explained.FIG. 3is a flowchart illustrating a procedure of the DVFS of the first embodiment.

<S302> The VFC12determines whether the location information change amount ΔLI calculated in the calculating parameter (S301) is more than 0. The location information change amount ΔLI more than 0 means that it is necessary to increase a voltage and a frequency of the target device. When the location information change amount ΔLI is more than 0 (YES in S302), increasing power consumption (S303) is performed. When the location information change amount ΔLI is equal to or lower than 0 (NO in S302), reducing power consumption (S311) is performed.

<Increasing power consumption (S303)> The VFC12increases power consumption of the target device under a predetermined condition. In the increasing power consumption (S303), the VFC12acts as a power controller. When the increasing power consumption (S303) is ended, the DVFS is ended.

<Reducing power consumption (S311)> The VFC12reduces power consumption of the target device under the predetermined condition. In the reducing power consumption (S311), the VFC12acts as the power controller. When the reducing power consumption (S311) is ended, the DVFS is ended.

That is, the VFC12ofFIG. 2dynamically controls the voltage and frequency of the target device based on the parameters calculated in the calculating parameter (S301) ofFIG. 3.

The increasing power consumption and reducing power consumption of the first embodiment will be explained below.FIG. 4is a flowchart illustrating a procedure of the increasing power consumption (S303) ofFIG. 3.FIG. 5is a flowchart illustrating a procedure of the reducing power consumption (S311) ofFIG. 3.

FIG. 4illustrates the increasing power consumption when the low power consumption mode LP is set.

<S401> The VFC12determines whether the first cycle number C1is lower than the predetermined first threshold TH1. The first cycle number C1lower than the first threshold TH1means that the location information LI changes in a short period of time. When the first cycle number C1is lower than the predetermined first threshold TH1(YES in S401), generating VCS (increasing voltage) (S402) is performed. When the first cycle number C1is not lower than the first threshold TH1(NO in S401), the increasing power consumption is ended.

<Generating VCS (increasing voltage) (S402)> The VFC12generates the control signal VCS in order to increase the voltage at the target device. Then, the VFC12outputs the generated control signal VCS to the target device, thereby increasing the voltage at the target device. In the generating VCS (increasing voltage) (S402), the VFC12acts as a voltage controller.

<S403> The VFC12determines whether the increasing voltage at the target device by the control signal VCS generated in the generating VCS (increasing voltage) (S402) is ended (whether the voltage at the target device becomes constant). When the voltage at the target device has increased (YES in S403), generating FCS (increasing frequency) (S404) is performed. When the voltage at the target device is increasing (NO in S403), the VFC12waits until the voltage at the target device has increased.

<Generating FCS (increasing frequency) (S404)> The VFC12generates the control signal FCS in order to increase the frequency of the target device. Then, the VFC12outputs the generated control signal FCS to the target device, thereby increasing the frequency of the target device. In the generating FCS (increasing frequency) (S404), the VFC12acts as a frequency controller. When the generating FCS (increasing frequency) (S404) is ended, the increasing power consumption is ended.

The reducing power consumption ofFIG. 5is the reducing power consumption when the low power consumption mode LP is set.

<S501> The VFC12determines whether location information change amount ΔLI is 0. When the location information change amount ΔLI is 0 (YES in S501),5502is performed. When the location information change amount ΔLI is lower than 0 (NO in S501), generating FCS (reducing frequency) (S503) is performed.

<S502> The VFC12determines whether the second cycle number C2is more than the second threshold TH2. The second cycle number C2more than the second threshold TN2means that the location information LI does not change for at least a predetermined period. When the second cycle number C2is more than the second threshold TH2(YES in S502), the generating FCS (reducing frequency) (S503) is performed. When the second cycle number C2is equal to or lower than the second threshold TH2(S502—NO), S504is performed.

<Generating FCS (reducing frequency) (S503)> The VFC12generates the control signal FCS in order to reduce the frequency of the target device. Then, the VFC12outputs the generated control signal FCS to the target device, thereby reducing the frequency of the target device. In the generating FCS (reducing frequency) (S503), the VFC12acts as the frequency controller.

<S504> The VFC12determines whether the third cycle number C3is more than the third threshold TH3. The third cycle number C3more than the third threshold TH3means that the location information LI is not continuously increased in at least a predetermined period. When the third cycle number C3is more than the third threshold TH3(YES in S504), S505is performed. When the third cycle number C3is equal to or lower than the third threshold TH3(NO in S504), the reducing power consumption is ended.

<S505> The VFC12determines whether a voltage V at the target device is more than the threshold voltage VTH. The voltage V more than the threshold voltage VTH means that it is necessary to reduce the voltage at the target device. When the voltage V at the target device is more than the threshold voltage VTH (YES in S505), generating VCS (reducing frequency) (S506) is performed. When the voltage V at the target device is equal to or lower than the threshold voltage VTH (NO in S505), the reducing power consumption is ended.

<Generating VCS (reducing voltage) (S506)> The VFC12generates the control signal VCS in order to reduce the voltage at the target device. Then, the VFC12outputs the generated control signal VCS to the target device, thereby reducing the voltage at the target device. In the generating VCS (reducing voltage) (S506), the VFC12acts as the voltage controller. When the generating VCS (reducing voltage) (S506) is ended, the reducing power consumption is ended.

A specific example of the DVFS of the first embodiment will be explained below.FIGS. 6 to 9are schematic diagrams illustrating transitions in voltage and frequency in the increasing power consumption (S303) and the reducing power consumption (S311) ofFIG. 3.

FIG. 6illustrates a state in a period of T0to T1. At a time T0, the location information LI has the value of 0, and the target device has the voltage of 0.9 [V] and the frequency of 50 [MHz]. That is, the target device is operated at the minimum voltage and the minimum frequency.

In the period of T0to T1, the frequency of the target device is maintained at 50 [MHz], and the voltage at the target device is maintained at 0.9 [V].

FIG. 7illustrates a state in a period of T1to T2. At the time T1, because the value of the location information LI is increased from 0 to 1 (that is, “ΔLI>0”) (YES in S302), the increasing power consumption (S303) is performed. In this increasing power consumption (S303), the generating VCS (increasing voltage) (S402) is performed because the first cycle number C1(=T1−T0) is lower than the first threshold TH1(YES in S401). Therefore, the increasing voltage at the target device is started.

In the period of T1to T2, the voltage at the target device is increased, and the frequency of the target device is maintained at 50 [MHz].

At the time T2, when the voltage at the target device has increased (YES in S403), the generating FCS (increasing frequency) (S404) is performed. Therefore, the voltage at the target device reaches 1.0 [V], and the frequency of the target device reaches 100 [MHz].

FIG. 8illustrates a state in a period of T2to T4. In the period of T2to T3, the increasing power consumption (S303) is performed four times because the value of the location information LI is increased from 1 to 5 in each one index (that is, “ΔLI>0”) (YES in S302). In each increasing power consumption (S303), the generating VCS (increasing voltage) (S402) and the generating FCS (increasing frequency) (S404) is not performed because the first cycle number C1is not lower than the first threshold TH1(NO in S401). As a result, the voltage at the target device is maintained at 1.0 [V], and the frequency of the target device is maintained at 100 [MHz].

In the period of T3to T4, the voltage at the target device is maintained at 1.0 [V], and the frequency of the target device is maintained at 100 [MHz].

At the time T4ofFIG. 8, the reducing power consumption (S311) is performed because the value of the location information LI is reduced from 5 to 4 (that is, “ΔLI<0”) (NO in S302). In this reducing power consumption (S311), the generating FCS (reducing frequency) (S503) is performed because of “ΔLI<0” (NO in S501). Therefore, the frequency of the target device reaches 50 [MHz]. Further, in this reducing power consumption (S311), the generating VCS (reducing voltage) (S506) is not performed because the third cycle number C3(=T4−T3) is equal to or lower than the third threshold TH3(NO in S504). Therefore, the voltage at the target device is maintained at 1.0 [V].

FIG. 9illustrates a state in a period of T4to T7. In the period of T4to T5, the voltage at the target device is maintained at 1.0 [V], and the frequency of the target device is maintained at 50 [MHz].

At the time T5, the reducing power consumption (S311) is performed because the location information LI has the value of 4 (that is, “ΔLI=0”) (NO in S302). In this reducing power consumption (S311), the generating FCS (reducing frequency) (S503) is not performed because the location information change amount ΔLI is equal to 0 while the second cycle number C2(=T5−T4) is equal to or lower than the second threshold (NO in S502). Therefore, the frequency of the target device is maintained at 50 [MHz]. Further, in this reducing power consumption (S311), the generating VCS (reducing voltage) (S506) is performed because the third cycle number C3(=T5−T3) is more than the third threshold TH3(YES in S504) while the voltage V (=1.0 [V]) at the target device is more than the threshold voltage VTH (YES in S505). Therefore, the reducing voltage at the target device is started.

In the period of T5to T6, the voltage at the target device is reduced, and the frequency of the target device is maintained at 50 [MHz].

At the time T6, the voltage at the target device reaches 0.9 [V], and the frequency of the target device is maintained at 50 [MHz].

In the period of T6to T7, the voltage at the target device is maintained at 0.9 [V], and the frequency of the target device is maintained at 50 [MHz].

For the increasing power consumption in setting the high speed mode HS, S401is omitted in the increasing power consumption ofFIG. 4. That is, in the high speed mode HS, the generating VCS (increasing voltage) (S402) is always performed.

For the reducing power consumption in setting the high speed mode HS, S502is omitted in the reducing power consumption ofFIG. 5. That is, in the high speed mode HS, the generating FCS (reducing frequency) (S503) is performed only when the location information change amount ΔLI is lower than 0.

According to the first embodiment, the semiconductor integrated circuit1includes the adjuster11and the VFC12. The adjuster11adjusts the data transmission and reception by tentatively holding the data transmitted and received among the plural devices. The VFC12controls the power consumption of at least one target device of the plural devices based on the location information LI indicating the location of the data held by the adjuster11. That is, the VFC12calculates the location information change amount ΔLI and the first cycle number C1to third cycle number C3relating to the change of the location information, and controls the power consumption of the target device according to the calculation result. As a result, the versatility and reusability of the VFC12can be improved.

Second Embodiment

A second embodiment will be explained below. In the second embodiment, the DVFS is described by way of example when the target device is the master device. The descriptions of contents similar to those of the first embodiment will not be repeated.

The DVFS of the second embodiment will be explained.FIG. 10is a flowchart illustrating a procedure of the DVFS of the second embodiment.

<S1002> The VFC12determines whether the location information change amount ΔLI calculated in the calculating parameter (S1001) is lower than 0. The location information change amount ΔLI lower than 0 means that it is necessary to increase the voltage and frequency of the target device. When the location information change amount ΔLI is lower than 0 (YES in S1002), increasing power consumption (S1003) is performed. When the location information change amount ΔLI is not lower than 0 (NO in S1002), reducing power consumption (S1011) is performed.

<Increasing power consumption (S1003)> The VFC12performs the increasing power consumption (S1003) of the target device under a predetermined condition. In the increasing power consumption (S1003), the VFC12acts as the power controller. When the increasing power consumption (S1003) is ended, the DVFS is ended.

<Reducing power consumption (S1011)> The VFC12performs reducing power consumption (S1011) of the target device under a predetermined condition. In the reducing power consumption (S1011), the VFC12acts as the power controller. When the reducing power consumption (S1011), the DVFS is ended.

That is, the VFC12ofFIG. 2dynamically controls the voltage and frequency of the target device based on the parameters calculated in the calculating parameter (S1001) ofFIG. 10.

The increasing power consumption and reducing power consumption of the second embodiment will be explained below.FIG. 11is a flowchart illustrating a procedure of the reducing power consumption (S1011) ofFIG. 10.

The increasing power consumption (S1003) ofFIG. 10is similar to that (the increasing power consumption (S303) ofFIG. 3) of the first embodiment (seeFIG. 4).

FIG. 11illustrates the reducing power consumption when the low power consumption mode LP is set.

<S1101> The VFC12determines whether location information change amount ΔLI is 0. When the location information change amount ΔLI is 0 (YES in S1101), S1102is performed. When the location information change amount ΔLI is more than 0 (NO in S1101), generating FCS (reducing frequency) (S1103) is performed.

<S1102> S1102is similar to that (S502ofFIG. 5) of the first embodiment.

<S1104> The VFC12determines whether the fourth cycle number C4is more than the fourth threshold TH4. The fourth cycle number C4more than the fourth threshold TH4means that the location information LI is not continuously reduced in at least a predetermined period. When the fourth cycle number C4is more than the fourth threshold TH4(YES in S1104), S1105is performed. When the fourth cycle number C4is equal to or lower than the fourth threshold TH4(NO in S1104), the reducing power consumption is ended.

<S1105> S1105is similar to that (S504ofFIG. 5) of the first embodiment.

A specific example of the DVFS of the second embodiment will be explained below.FIGS. 12 to 15are schematic diagrams illustrating transitions in voltage and frequency in the increasing power consumption (S1003) and reducing power consumption (S1011) ofFIG. 10.

FIG. 12illustrates a state in a period of T0to T1. At the time T0, the location information LI has the value of 1, and the target device has the voltage of 0.9 [V] and the frequency of 50 [MHz]. That is, the target device is operated at the minimum voltage and the minimum frequency.

In the period of T0to T1, the frequency of the target device is maintained at 50 [MHz], and the voltage at the target device is maintained at 0.9 [V].

FIG. 13illustrates a state in a period of T1to T2. At the time T1, the increasing power consumption (S1003) is performed because the value of the location information LI is reduced from 1 to 0 (that is, “ΔLI<0”) (YES in S1002). In this increasing power consumption (S1003), the generating VCS (increasing voltage) (S402) is performed because the first cycle number C1(=T1−T0) is lower than the first threshold TH1(YES in S401). Therefore, the increasing voltage at the target device is started.

In the period of T1to T2, the voltage at the target device is increased, and the frequency of the target device is maintained at 50 [MHz].

At the time T2, the voltage at the target device has increased (YES in S403), the generating FCS (increasing frequency) (S404) is performed. Therefore, the voltage at the target device reaches 1.0 [V], and the frequency of the target device reaches 100 [MHz].

FIG. 14illustrates a state in a period of T2to T4. In the period of T2to T3, the voltage at the target device is maintained at 1.0 [V], and the frequency of the target device is maintained at 100 [MHz].

At the time t3ofFIG. 14, the reducing power consumption (S1011) is performed because the value of the location information LI is maintained at 0 (that is, “ΔLI=0”) (NO in S1002). In this reducing power consumption (S1011), the generating VCS (reducing frequency) (S1103) is not performed because the second cycle number C2(=T3−T2) is equal to or lower than the second threshold TH2(NO in S1102). Therefore, the frequency of the target device is maintained at 50 [MHz]. Further, in this reducing power consumption (S1011), the generating VCS (reducing voltage) (S1106) is not performed because the fourth cycle number C4(=T3−T1) is lower than the fourth threshold TH4(NO in S1104). Therefore, the voltage at the target device is maintained.

In the period of T3to T4, the voltage at the target device is maintained at 1.0 [V], and the frequency of the target device is maintained at 100 [MHz].

At the time T4, the reducing power consumption (S1011) is performed because the value of the location information LI is increased from 0 to 1 (that is, “ΔLI>0”) (NO in S1002). In this reducing power consumption (S1011), the generating FCS (reducing frequency) (S1103) is performed because of “ΔLI>0” (NO in S1101). Therefore, the frequency of the target device reaches 50 [MHz]. Further, in this reducing power consumption (S1011), the generating VCS (reducing voltage) (S1106) is not performed because the fourth cycle number C4(=T4−T2) is equal to or lower than the fourth threshold TH4(NO in S1104). Therefore, the voltage at the target device is maintained at 1.0 [V].

FIG. 15illustrates a state in a period of T4to T7. In the period of T4to T5, the voltage at the target device is maintained at 1.0 [V], and the frequency of the target device is maintained at 50 [MHz].

At the time T5, the reducing power consumption (S1011) is performed because the value of the location information LI is maintained at 1 (that is, “ΔLI=0”) (NO in S1002). In this reducing power consumption (S1011), the generating FCS (reducing frequency) (S1103) is not performed because the location information change amount ΔLI is 0 while the second cycle number C2(=T5−T4) is equal to or lower than the second threshold (NO in S1102). Therefore, the frequency of the target device is maintained at 50 [MHz]. Further, in this reducing power consumption (S1011), the generating VCS (reducing voltage) (S1106) is performed because the fourth cycle number C4(=T4−T2) is more than the fourth threshold TH4(YES in S1104) while the voltage V (=1.0 [V]) at the target device is more than the threshold voltage VTH (YES in S1105). Therefore, the reducing voltage at the target device is started.

In the period of T5to T6, the voltage at the target device is reduced, and the frequency of the target device is maintained at 50 [MHz].

At the time T6, the voltage at the target device reaches 0.9 [V], and the frequency of the target device is maintained at 50 [MHz].

In the period of T6to T7, the voltage at the target device is maintained at 0.9 [V], and the frequency of the target device is maintained at 50 [MHz].

For the increasing power consumption in setting the high speed mode HS, S402is omitted in the increasing power consumption ofFIG. 4. That is, in the high speed mode HS, the generating VCS (increasing voltage) (S402) is always performed.

For the reducing power consumption in setting the high speed mode HS, S1102is omitted in the reducing power consumption ofFIG. 11. That is, in the high speed mode HS, the generating FCS (reducing frequency) (S1103) is performed only when the location information change amount ΔLI is more than 0.

According to the second embodiment, the VFC12controls the power consumption of the target device according to the location information change amount ΔLI, and the first cycle number C1, second cycle number C2and fourth cycle number C4, which relate to the change of the location information. As a result, the versatility and reusability of the VFC12can be improved.

Third Embodiment

A third embodiment will be explained below. In the third embodiment, the DVFS is explained for the plural target devices by way of example. The descriptions of contents similar to those of the first and second embodiments will not be repeated.

In the third embodiment, the adjuster11ofFIG. 2simultaneously acts as the slave device having the function of receiving the data D transmitted from the master device and as the master device having the function of transmitting the data D to the slave device.

Selecting mode of the third embodiment will be explained below.FIG. 16is a flowchart illustrating a procedure of the selecting mode of the third embodiment.

The selecting mode is performed prior to the DVFS ofFIG. 3orFIG. 10.

<Determining operation mode (S1601)> The VFC12determines which the increasing power consumption or the reducing power consumption should be performed to each of the master device that is a source of the data D and the slave device that is a destination of the data D. In the determining operation mode (S1601), the VFC12acts as an operation mode determining unit. For example, the VFC12determines the operation mode of the slave device similarly to S302ofFIG. 3, and determines the operation mode of the master device similarly to S1002ofFIG. 10.

<S1602> The VFC12determines whether plural determined results of the determining operation mode (S1601) are different from each other. When the plural determined results are different from each other (YES in S1602), S1603is performed. When the plural determined results equal to each other (NO in S1602), DVFS (S1611) is performed.

<S1603> The VFC12determines which is the operation mode. When the operation mode is the high speed mode HS (A in S1603), the increasing power consumption (S1604) is performed. When the operation mode is the low power consumption mode LP (B in S1603), reducing power consumption (S1621) is performed.

<Increasing power consumption (S1604)> The increasing power consumption (S1604) is similar to that (increasing power consumption (S303) ofFIG. 3) of the first embodiment. When the increasing power consumption (S1604) is ended, the selecting mode is ended.

<DVFS (S1611)> For the slave device, the DVFS (S1611) is similar to that of the first embodiment (seeFIG. 3). For the master device, the DVFS (S1611) is similar to that of the second embodiment (seeFIG. 10). When the DVFS (S1611) is ended, the selecting mode is ended.

<Reducing power consumption (S1621)> For the slave device, the reducing power consumption (S1621) is similar to the reducing power consumption (S311) ofFIG. 3of the first embodiment (seeFIG. 5). For the master device, the reducing power consumption (S1621) is similar to the reducing power consumption (S1011) ofFIG. 10of the second embodiment (seeFIG. 11). When the reducing power consumption (S1621) is ended, the selecting mode is ended.

According to the third embodiment, in the case of the plural target devices, the VFC12ofFIG. 2determines which the increasing power consumption or the reducing power consumption (S1621) should be performed to each of the target devices. When the plural determined results are different from each other, the VFC12performs the reducing power consumption (S1621) in setting the low power consumption mode in which the target device is operated in the low power consumption, and the VFC12performs the increasing power consumption (S1604) in setting the high speed mode in which the target device is operated at high speed. That is, in the case that the adjuster11processes both data D in the transmission channel and in the reception channel, and when the operation mode of the target device (slave device) of the transmission channel is different from that of the target device (master device) of the reception channel, the VFC12selects the increasing power consumption (S1604) and the reducing power consumption (S1621) according to the operation mode. As a result, in the case of the plural channels, the versatility and reusability of the VFC12can be improved.

Fourth Embodiment

A fourth embodiment will be explained below. In the fourth embodiment, the low power consumption processing is performed when the operating environment of the target device is abnormal. The descriptions of contents similar to those of the first to third embodiments will not be repeated.

Selecting mode of the fourth embodiment will be explained below.FIG. 17is a flowchart illustrating a procedure of the selecting mode of the fourth embodiment.

The selecting mode is performed prior to the DVFS ofFIG. 3orFIG. 10.

<S1701> The VFC12determines whether there is an interrupt signal IS. When there is the interrupt signal IS (YES in S1701), changing threshold (S1702) is performed. When there is not the interrupt signal IS (NO in S1701), DVFS (S1711) is performed.

<Changing threshold (S1702)> The VFC12changes the second threshold TH2to fourth threshold TH4to 0. Therefore, the generating FCS (reducing frequency) (S503), the generating VCS (reducing voltage) (S506), the generating FCS (reducing frequency) (S1103), and the generating VCS (reducing voltage) (S1106) can be performed in the reducing power consumption (S1703) irrespective of the values of the second cycle number C2to fourth cycle number C4.

<Reducing power consumption (S1703)> For the slave device, the reducing power consumption (S1703) is similar to the reducing power consumption (S311) ofFIG. 3of the first embodiment (seeFIG. 5). For the master device, the reducing power consumption (S1703) is similar to the reducing power consumption (S1011) ofFIG. 10of the second embodiment (seeFIG. 11). When the reducing power consumption (S1703) is ended, the selecting mode is ended.

<DVFS (S1711)> For the slave device, the DVFS (S1711) is similar to that of the first embodiment (seeFIG. 3). For the master device, the DVFS (S1711) is similar to that of the second embodiment (seeFIG. 10). When the DVFS (S1711) is ended, the selecting mode is ended.

The monitor13cancels the interrupt signal IS when the operating environment of the target device becomes normal. Therefore, the DVFS (S1711) can be performed.

According to the fourth embodiment, the VFC12ofFIG. 2performs the reducing power consumption (S1703) in order to reduce the power consumption of the target device when the monitor13detects that the operating environment of the target device is abnormal. That is, the VFC12performs the reducing power consumption (S1703) when the operating environment of the target device is abnormal. As a result, the damage to the target device can be prevented. The damage is caused by increasing power consumption of the target device when the operating environment of the target device is abnormal.

At least a portion of a VFC12according to the above-described embodiments may be composed of hardware or software. When at least a portion of the VFC12is composed of software, a program for executing at least some functions of the VFC12may be stored in a recording medium, such as a flexible disk or a CD-ROM, and a computer may read and execute the program. The recording medium is not limited to a removable recording medium, such as a magnetic disk or an optical disk, but it may be a fixed recording medium, such as a hard disk or a memory.

In addition, the program for executing at least some functions of the VFC12according to the above-described embodiment may be distributed through a communication line (which includes wireless communication) such as the Internet. In addition, the program may be encoded, modulated, or compressed and then distributed by wired communication or wireless communication such as the Internet. Alternatively, the program may be stored in a recording medium, and the recording medium having the program stored therein may be distributed.