Abstract:
The data processor for processing operation data stored in a memory connected to an external bus in the order of operations includes: an interface section for holding a parameter required for transfer of the operation data; an operation section receiving the operation data from the interface section for performing predetermined processing; and an operation memory for storing the operation data transferred. The interface section sequentially transfers the operation data from the memory connected to the external bus to the operation memory using the parameter, and sequentially transfers the operation data from the operation memory to the operation section.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a data processor for processing data transferred from a system bus and a data transfer method employed by the data processor.  
           [0002]    [0002]FIG. 20 is a block diagram of a conventional data processor. The data processor of FIG. 20 is a drawing processor including a host CPU  91  for control of the entire drawing apparatus, a main memory  92  used by the host CPU  91 , a drawing processing unit  93 , a drawing memory  94  and a main bus  95 .  
           [0003]    The drawing processing unit  93  includes a CPU interface  96  functioning as the interface with the host CPU  91 , a data processing section  97 , and a drawing memory interface  98  functioning as the interface with the drawing memory  94 . The data processing section  97  performs issuance of an interrupt request to the host CPU  91  and the like when data processing under control of the host CPU  91  via the CPU interface  96  and supply of data to be processed are necessary and in other occasions. The drawing memory  94  includes a drawing command region and a frame region, and stores drawing data in the drawing command region and drawing-processed data in the frame region. The main bus  95  connects the host CPU  91 , the main memory  92  and the drawing processing unit  93  with one another.  
           [0004]    In the conventional data processor described above, supply of data to the drawing processing unit  93  is totally performed under control of the host CPU  91 . To state specifically, when supply of data is necessary, the drawing processing unit  93  sends an interrupt signal IS to the host CPU  91  to request an interrupt. Receiving the interrupt, the host CPU  91  supplies data to the drawing processing unit  93  to be stored in the drawing memory.  
           [0005]    In general, for reduction in power consumption, supply of a clock signal is partly halted depending on the operation mode of an apparatus, and power supply is turned off depending on the operation mode. Also, as disclosed in Japanese Laid-Open Patent Publication No. 9-319453, for example, the following measures are taken to reduce power consumption. A processor or the like halts supply of a clock signal or power to an unused operator according to an instruction, or supplies a clock signal or power only to a portion of a register or an operator related to eight lower-order bits, for example, depending on the bit length of an instruction.  
           [0006]    However, when a drawing apparatus as shown in FIG. 20 is used to construct a system such as a car navigation system, the performance of the CPU is lost by frequent occurrence of data transfer, resulting in deterioration in the performance as the system. To suppress the deterioration in performance, the capacities of the drawing memory and the main memory may be increased. However, this disadvantageously increases the cost.  
           [0007]    A digital signal processor (DSP), an application-specific integrated circuit (ASIC) and the like are controlled under instructions from the host CPU controlling these devices.  
           [0008]    Therefore, when reduction in power consumption is intended for the DSP, ASIC and the like, only macro control is permitted in which processing is halted from start to end in a certain internal operator while processing is performed from start to end in another internal operator. For this reason, delicate power control to an internal block level is not possible when different internal parts operate with different processing data items.  
         SUMMARY OF THE INVENTION  
         [0009]    An object of the present invention is providing a data processor capable of lightening the load of a host CPU during data transfer.  
           [0010]    Another object of the present invention is providing a data processor with reduced power consumption.  
           [0011]    According to the present invention, the data processor, which is controlled by an external bus master such as a host CPU, includes a control register for holding information such as an address at which data to be processed is stored and the number of words to be transferred, so that the data processor itself can serve as a bus master to perform data transfer to an operation memory without putting a load on the external bus master.  
           [0012]    To state specifically, the present invention is directed to a data processor for processing operation data stored in a memory connected to an external bus in the order of operations, including: an interface section for holding a parameter required for transfer of the operation data; an operation section receiving the operation data from the interface section for performing predetermined processing; and an operation memory for storing the operation data transferred, wherein the interface section sequentially transfers the operation data from the memory connected to the external bus to the operation memory using the parameter, and sequentially transfers the operation data from the operation memory to the operation section.  
           [0013]    With the above configuration, the data processor itself transfers operation data according to the parameter held by the control register, to acquire the data. This lightens the load related to data transfer processing on the external bus master such as a host CPU.  
           [0014]    In the data processor described above, preferably, the interface section transfers transfer information for transfer of operation data to be next processed to the operation memory, together with the operation data, and when reading the transfer information from the operation memory, the interface section sequentially transfers the operation data corresponding to the transfer information from the memory connected to the external bus to the operation memory.  
           [0015]    With the above configuration, the data processor can read transfer information for transfer of operation data to be processed next, and thus the data processor itself can start DMA transfer and acquire the operation data. This prevents the external bus master controlling the external bus from being loaded with parameter setting when parameters for DMA transfer must be set repeatedly, for example, when an operation data group must be divided for transfer because the capacity of the operation memory is limited, and when operation data groups must be sequentially generated and transferred to the data processing section.  
           [0016]    Preferably, the data processor described above further includes a data transfer management section for holding information indicating whether or not the interface section is under transfer of the operation data.  
           [0017]    With the above configuration, the data processor is provided with the data transfer management section that makes a notification of completion of DMA transfer instructed from the external bus master. This makes it possible to overwrite a region of the memory connected to the external bus from which data has already been read, and thus eliminates the necessity of unduly increasing the capacity of the memory connected to the external bus. The cost of the data processor can therefore be reduced.  
           [0018]    In the data processor described above, preferably, the interface section notifies an external bus master controlling the external bus of termination of transfer of the operation data by generating an interrupt.  
           [0019]    With the above configuration, the data processor itself can notify the external bus master of the status of data transfer. Therefore, the external bus master can timely know the timings of preparation of data required for the next operation, transfer of the data to the memory connected to the external bus, and the like.  
           [0020]    In the data processor described above, preferably, the interface section includes a data transfer wait register holding information set by the external bus master controlling the external bus when start of transfer of the operation data is newly required, and halts the current transfer of the operation data according to the information held by the data transfer wait register.  
           [0021]    With the above configuration, in occurrence of sudden data change, the interface section can halt currently-running DMA transfer and start new transfer.  
           [0022]    In the data processor described above, preferably, the operation section includes a plurality of circuits for processing commands included in the operation data, and the interface section supplies a clock signal to a circuit among the plurality of circuits that processes a command included in the operation data transferred to the operation section according to a control field of the command.  
           [0023]    With the above configuration, a portion of the operation section required for the next processing is known prior to transfer of data for the processing to the operation section. Therefore, the clock signal can be supplied under control only to the portion of which activation is actually required. Thus, reduction in power consumption is possible.  
           [0024]    Preferably, the interface section starts supply of the clock signal according to a first control field located at the head of the command, and halts the supply of the clock signal according to a second control field located at the end of the command.  
           [0025]    With the above configuration, supply of the clock can be started before start of a command and halted after the processing of the command.  
           [0026]    Preferably, the circuit of the operation section receiving the clock signal outputs a done signal indicating termination of the processing of the transferred command to the interface section, and the interface section starts supply of the clock signal according to a control field located at the head of the command, and halts the supply of the clock signal to the circuit that has outputted the done signal upon receipt of the done signal.  
           [0027]    With the above configuration, each circuit of the operation section itself halts supply of the clock signal after termination of processing. Therefore, the interface section is relieved of timing control for halting the clock signal. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]    [0028]FIG. 1 is a block diagram of a data processor of Embodiment 1 of the present invention.  
         [0029]    [0029]FIG. 2 is an illustration of an example of arrangement of data stored in a drawing memory shown in FIG. 1.  
         [0030]    [0030]FIG. 3 is an illustration of an example of arrangement of data stored in a main memory shown in FIG. 1.  
         [0031]    [0031]FIG. 4 is an illustration of an example of parameters held by a control register shown in FIG. 1.  
         [0032]    [0032]FIG. 5 is a flowchart of processing by the data processor of FIG. 1.  
         [0033]    [0033]FIG. 6 is a flowchart of processing by a data processor of the first alteration to Embodiment 1 of the present invention.  
         [0034]    [0034]FIG. 7 is a flowchart of processing by a data processor of the second alteration to Embodiment 1 of the present invention, showing processing related to a host CPU shown in FIG. 1.  
         [0035]    [0035]FIG. 8 is a flowchart of processing by the data processor of the second alteration to Embodiment 1 of the present invention, showing processing related to a drawing processing unit shown in FIG. 1.  
         [0036]    [0036]FIG. 9 is a block diagram of a data processor of Embodiment 2 of the present invention.  
         [0037]    [0037]FIG. 10 is a flowchart of processing by the data processor of FIG. 9, showing processing related to a host CPU.  
         [0038]    [0038]FIG. 11 is a flowchart of processing by the data processor of FIG. 9, showing processing related to a drawing processing unit.  
         [0039]    [0039]FIG. 12 is an illustration of an example of parameters held by a control register shown in FIG. 9.  
         [0040]    [0040]FIG. 13 is a block diagram of a data processor of Embodiment 3 of the present invention.  
         [0041]    [0041]FIG. 14 is an illustration of an example of parameters held by a control register shown in FIG. 13.  
         [0042]    [0042]FIG. 15 is a block diagram of a data processor of Embodiment 4 of the present invention.  
         [0043]    [0043]FIG. 16 is an illustration of an example of drawing commands received by a prefetch section shown in FIG. 15.  
         [0044]    [0044]FIG. 17 is a diagrammatic illustration of a case of control of supply of a clock signal without use of a predecoder.  
         [0045]    [0045]FIG. 18 is a block diagram of a data processor of Embodiment 5 of the present invention.  
         [0046]    [0046]FIG. 19 is a block diagram of an example of details of a drawing section and a memory interface shown in FIG. 18.  
         [0047]    [0047]FIG. 20 is a block diagram of a conventional data processor. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0048]    Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Note that in the embodiments to follow, described are data processors performing drawing as an example of operation. Note herein that operation data includes both commands such as drawing commands and data and the like used for execution of the commands.  
         [0049]    Embodiment 1  
         [0050]    [0050]FIG. 1 is a block diagram of a data processor of Embodiment 1 of the present invention. The data processor of FIG. 1 includes a host CPU  10 , a main memory  20 , a drawing processing unit  30 , a drawing memory  40  as the operation memory, a main bus  5  as the external bus (system bus), an I/O block  6  and a DVD-ROM  7 .  
         [0051]    The host CPU  10  controls the data processor of FIG. 1 in various ways. The main memory  20  stores drawing commands sent from the host CPU  10  and other kinds of data. The drawing processing unit  30 , activated by the host CPU  10 , performs drawing processing. The drawing memory  40  stores drawing commands required for the drawing processing unit  30  to perform drawing and frame data for a display screen. The main bus  5  connects the host CPU  10 , the main memory  20  and the drawing processing unit  30  with one another. The I/O block  6  connects the DVD-ROM  7  with the main bus  5 . A database of drawing data is stored in the DVD-ROM  7 .  
         [0052]    The host CPU  10  includes a bus controller  11  serving as both an interface with the main bus  5  and an arbitrator for the main bus  5 . The drawing processing unit  30  includes a CPU interface  31 , a drawing section  32  as an operator for actually performing drawing processing, and a memory interface  33 . The CPU interface  31  and the memory interface  33  constitute an interface section  39 .  
         [0053]    The CPU interface  31 , functioning as an interface with the main bus  5 , includes a direct memory access (DMA) controller  34 . The DMA controller  34  includes a control register  35  for holding parameters required for DMA transfer, and controls data transfer between the main memory  20  and the drawing processing unit  30 . The memory interface  33  functions as an interface with the drawing memory  40 . The memory interface  33  also performs data transfer with the CPU interface  31  and data transfer with the drawing section  32 .  
         [0054]    [0054]FIG. 2 illustrates an example of arrangement of data stored in the drawing memory  40  shown in FIG. 1. In this example, transfer information on a drawing command group to be transferred and read subsequent to the current drawing command group stored in the drawing memory  40  is transferred simultaneously with the DMA transfer of the current drawing command group at the end of the current drawing command group. The transfer information on the next drawing command group includes the drawing command address in the main memory  20  as the transfer source, the number of words to be transferred, and the drawing command address in the drawing memory  40  as the transfer destination (hereinafter, these items of information are collectively called next drawing command address information).  
         [0055]    The drawing memory  40  has an area corresponding to a 16-bit address space. A half of the area is used as a drawing command region and the remainder as a frame region. As shown in FIG. 2, the drawing memory  40  stores the next drawing command address information together with a transfer instruction at the end of the current drawing command group stored in the drawing command region.  
         [0056]    As the drawing processing proceeds, the drawing section  32  retrieves and decodes the transfer instruction. Once decoding the transfer instruction, the drawing section  32  outputs a Done signal DS to the DMA controller  34  as a transfer request. Upon receipt of the Done signal DS, the DMA controller  34  sets the next drawing command address information in the control register  35  and outputs a transfer request signal TR. The CPU interface  31  then starts DMA transfer according to the information held by the control register  35 .  
         [0057]    In the illustrated example, the drawing section  32  retrieves the transfer instruction. Alternatively, the DMA controller  34  may retrieve and decode the transfer instruction. In this case, transfer of the transfer instruction to the drawing section  32  is not required. In FIG. 2, the next drawing command address information is stored at the end of the current drawing command group transferred to the drawing memory  40 . Alternatively, next drawing command address information may be located at the head of the current drawing command group transferred, or in the middle of the current drawing command group transferred. In these cases, a drawing command empty flag may be set when the transfer instruction is read from the drawing memory  40  to the drawing processing unit  30 , to enable the DMA controller  34  to detect shortage of drawing commands in the drawing memory  40  and issue the drawing command transfer request.  
         [0058]    [0058]FIG. 3 illustrates an example of arrangement of data stored in the main memory  20  shown in FIG. 1. The main memory  20  has an area corresponding to a 16-bit address space, and includes a data transfer management region operating as a data transfer manager at the head address, a drawing command region occupying roughly a half of the entire area, and a frame region as the remainder.  
         [0059]    In the drawing command region, drawing commands are stored in the order of drawing. In the data transfer management region, stored are an under-transfer flag asserted when DMA transfer is underway between the drawing processing unit  30  and the main memory  20 , and a transfer finish flag asserted when the DMA transfer is finished. The host CPU  10  reads these flags from the main memory  20  to detect whether or not overwrite of the drawing command group currently stored in the main memory  20  is possible. If overwrite is possible, the host CPU  10  places a drawing command group to be next transferred to the drawing processing unit  30  in the drawing command region of the main memory  20 .  
         [0060]    In the illustrated example, the data transfer management region is placed in the main memory  20  as a data transfer manager specifying the transfer state. Alternatively, a data transfer manager having a state register may be provided somewhere apart from the main bus  5 , in which both the host CPU  10  and the drawing processing unit  30  can set and monitor the respective transfer states in the state register. The data transfer manager with this configuration may notify the host CPU  10  and the drawing processing unit  30  of the state of use of the main memory  20 .  
         [0061]    [0061]FIG. 4 illustrates an example of parameters held by the control register  35  shown in FIG. 1. The control register  35  holds a drawing command address in the main memory, the number of transfer words indicating the number of words of data to be transferred, a drawing command address in the drawing memory, and a parameter valid flag. The drawing command address in main memory indicates the head address of drawing commands in the main memory  20  in which the drawing commands are currently stored. The drawing command address in the drawing memory indicates the head address of the drawing commands in the drawing memory  40  into which the drawing commands are to be transferred and stored. The parameter valid flag is a flag used by the DMA controller  34  to notify that the parameters in the control register  35  have been read at the completion of the DMA transfer.  
         [0062]    [0062]FIG. 5 is a flowchart of processing by the data processor of FIG. 1. Note that this flowchart shows only drawing-related processing and does not show any other system-related processing performed by the host CPU  10 . The flow of basic processing performed by the data processor of FIG. 1 will be described with reference to FIGS. 1 and 5.  
         [0063]    In step S 11 , the data processor of FIG. 1 is activated, and the host CPU  10  reads necessary drawing data from the DVD-ROM  7  into the main memory  20 .  
         [0064]    In step S 12 , the host CPU  10  performs processing for the read data required for transfer of the data to the drawing processing unit  30 , and sends resultant drawing commands to the drawing command region of the main memory  20  shown in FIG. 3. The processing required before transfer of the data to the drawing processing unit  30  differs with the format of the drawing data stored in the DVD-ROM  7  and the configuration of the drawing processing unit  30 . Herein, assume that the processing includes preprocessing for drawing such as tilt calculation and graphic clipping for transfer of the data to the drawing processing unit  30 . Clipping is processing of cutting off a protrusion when part of a graphic protrudes from a certain limited space such as a display region.  
         [0065]    In step S 13 , the host CPU  10  sets the head address of the preprocessed drawing commands in the main memory  20 , the number of words to be transferred, and the destination address of the drawing commands in the drawing memory  40  as the destination in the control register  35  of the drawing processing unit  30 . In step S 14 , the DMA controller  34  sends an access request to the bus controller  11  operating as the bus arbitrator via the CPU interface  31 .  
         [0066]    In step S 15 , the DMA controller  34  determines whether or not bus use permission (bus use right) has been granted by the bus arbitrator (bus controller  11 ). If no bus use permission is granted, the process returns to step S 14 , and the DMA controller  34  continues sending a bus use request. Once bus use permission is granted, the process proceeds to step S 16 , where the DMA controller  34  performs DMA transfer of the drawing commands from the main memory  20  to the drawing memory  40  according to the addresses and the number of words set in the control register  35 .  
         [0067]    After completion of the DMA transfer of the set number of words, in step S 17 , the DMA controller  34  negates the parameter valid flag in the control register  35 , to notify that the parameters in the control register  35  have been read. The CPU interface  31  outputs a Run signal RS to the drawing section  32  to activate the drawing section  32  for start of drawing. In step S 18 , the drawing section  32  starts drawing.  
         [0068]    In step S 19 , the drawing section  32  determines whether or not the drawing for the drawing commands in the drawing memory  40  has been completed. If determining that the drawing has been completed, the drawing section  32  asserts the Done signal DS sent to the DMA controller  34 , and the process proceeds to step S 20 . Otherwise, the process returns to step S 18 .  
         [0069]    In step S 20 , upon receipt of the Done signal DS, the DMA controller  34  examines the parameter valid flag set in the control register  35  to determine whether or not new next drawing command address information has been set. If no new next drawing command address information has been set, that is, the parameter valid flag stays negated, the DMA controller  34  terminates the processing and waits for setting of next drawing command address information. If the host CPU  10  has prepared new drawing commands in the main memory  20  and the parameter valid flag has been asserted during the time period from step S 17  through step S 19 , the process returns to step S 14  so that the DMA controller  34  can perform transfer and drawing of the new drawing commands.  
         [0070]    As described above, the drawing processing unit  30  itself can acquire drawing commands according to the parameters set by the host CPU  10 . Thus, since the drawing processing unit can take the load of data transfer processing that is conventionally put on the host CPU, the load on the host CPU during data transfer is lightened.  
         [0071]    (First Alteration to Embodiment 1)  
         [0072]    [0072]FIG. 6 is a flowchart of processing by a data processor of the first alteration to Embodiment 1 of the present invention. Note that this flowchart shows only drawing-related processing and does not show any other system-related processing performed by the host CPU  10 . The configuration of the data processor of this alteration is substantially the same as that of the data processor of FIG. 1. Therefore, the flow of processing performed by the data processor of the first alteration is described with reference to FIGS.  1  and  6 .  
         [0073]    Processing in steps S 31  and S 32  is substantially the same as the processing in steps S 11  and S 12  described above with reference to FIG. 5, and thus the description thereof is omitted here. In step S 33 , the host CPU  10  places next drawing command address information on a drawing command group intended to be transferred next to the coming transfer at the end of the drawing command group prepared in the main memory  20 . Processing in step S 34  is substantially the same as the processing in step S 13 .  
         [0074]    In step S 35 , the host CPU  10  determines whether or not it is necessary to generate drawing commands intended to be transferred next. If necessary, the process proceeds to step S 36 . Otherwise, the process proceeds to step S 41 , and the host CPU  10  terminates processing related to drawing and performs other processing.  
         [0075]    In step S 36 , the host CPU  10  prepares the next drawing commands in the region of the main memory  20  according to the next drawing command address information transferred to the drawing memory  40  together with the drawing commands.  
         [0076]    Processing in steps S 41  to S 45  is the same as the processing in steps S 14  to S 18  described above, except that in step S 42 , the process returns to step S 41  if no bus use permission is granted and otherwise proceeds to step S 43 . The description of these steps is therefore omitted here.  
         [0077]    In step S 46 , the drawing section  32  determines whether or not the drawing command retrieved from the drawing memory  40  is a transfer instruction. If the retrieved drawing command is a transfer instruction, the process proceeds to step S 48 . Otherwise, the process proceeds to step S 47 .  
         [0078]    In step S 47 , the drawing section  32  determines whether or not the drawing related to the drawing commands in the drawing memory  40  has been completed. If it is determined that the drawing has been completed, that is, if a drawing end instruction has been received, or if all the drawing commands transferred have been executed, the drawing section  32  asserts the Done signal DS sent to the DMA controller  34 , and terminates the processing. If it is determined that the drawing has not been completed, the process returns to step S 45 .  
         [0079]    In step S 48 , the drawing section  32  asserts the Done signal DS sent to the CPU interface  31 . On receipt of the Done signal DS, the CPU interface  31  sets the next command address information in the control register  35 . The process returns to step S 41  for execution of DMA transfer and drawing processing for the new drawing commands.  
         [0080]    As described above, in the first alteration, the drawing processing unit  30  itself can acquire drawing commands according to the parameters set by the host CPU  10 . In addition, since information on the address at which drawing commands required next are stored and the like is transferred together with the current drawing commands, the drawing processing unit  30  itself can start DMA transfer and acquire drawing commands. As a result, the host CPU can be relieved of the load of setting parameters for DMA transfer every time the transfer is performed in such cases that data must be divided into a plurality of parts for transfer due to limitation of the capacity of the drawing memory, that data is stored sporadically in the main memory, and that the host CPU must generate drawing command groups in sequence and transfer them to the drawing processing unit. This also enables continuous data transfer.  
         [0081]    Although only the transfer from the main memory  20  connected to the external bus to the drawing memory  40  was described, substantially the same procedure is adopted for data transfer from the drawing memory  40  to the drawing section  32 . That is, even when data is stored sporadically in the drawing memory  40 , continuous data read is possible based on the drawing command address in the drawing memory.  
         [0082]    (Second Alteration to Embodiment 1)  
         [0083]    [0083]FIGS. 7 and 8 are flowcharts of processing of a data processor of the second alteration to Embodiment 1 of the present invention, in which FIG. 7 shows processing related to the host CPU  10  in FIG. 1 and FIG. 8 shows processing related to the drawing processing unit  30  in FIG. 1. Note that the flowcharts of FIGS. 7 and 8 show only drawing-related processing and do not show any other system-related processing performed by the host CPU  10 . The configuration of the data processor of this alteration is substantially the same as that of the data processor of FIG. 1. Therefore, the flow of processing performed by the data processor of the second alteration is described with reference to FIGS. 1, 7 and  8 . In this alteration, the data transfer management region is used.  
         [0084]    Processing in steps S 51  to S 54  is substantially the same as the processing in steps S 31  to S 34  described above with reference to FIG. 6, and thus the description thereof is omitted here.  
         [0085]    In step S 55 , the host CPU  10  determines whether or not it is necessary to generate drawing commands intended to be transferred next. If necessary, the process proceeds to step S 56 . Otherwise, the process proceeds to step S 60 , in which the host CPU  10  terminates processing related to drawing and performs other processing.  
         [0086]    In step S 56 , the host CPU  10  examines whether or not the head address of drawing commands in the main memory  20  intended to be set next is the same as that in the previous setting. If the head address of the next drawing commands is the same as that in the previous setting, or coincides with the memory space in the main memory  20  in the previous setting, the process proceeds to step S 57 . Otherwise, if the head address of the next drawing commands is an address totally irrelevant to that in the previous setting, the process proceeds to step S 59 . In step S 59 , the host CPU  10  prepares the next drawing commands in the drawing command region of the main memory  20 , and the process returns to step S 55 .  
         [0087]    In step S 57 , the host CPU  10  examines the data transfer management region of the main memory  20  to check the transfer finish flag indicating whether or not the drawing procession section  30  has finished the transfer of the drawing commands. If the transfer has been finished, the process proceeds to step S 58 . Otherwise, step S 57  is repeated.  
         [0088]    In step S 58 , the host CPU  10  prepares the next drawing commands in the region of the main memory  20  from which the drawing commands have already been read (readout-finished region), and the process returns to step S 55 .  
         [0089]    After the next drawing command address information is set in the control register  35  by the host CPU  10  in step S 54 , the drawing processing unit  30  checks the parameter valid flag in step S 71  in FIG. 8. If the parameter valid flag is in the negated state, step S 71  is repeated and waits until the flag is asserted. When the parameter valid flag is in the asserted state, the process proceeds to step S 72 .  
         [0090]    In step S 72 , the drawing processing unit  30  asserts the under-transfer flag in the data transfer management region of the main memory  20 . Processing in steps S 73  to S 76  and S 78  is substantially the same as the processing in steps S 41  to S 45  described with reference to FIG. 6, and thus the description thereof is omitted here. In step S 77 , the DMA controller  34  asserts the transfer finish flag in the data management region of the main memory  20 .  
         [0091]    In step S 79 , the drawing section  32  determines whether or not the drawing command retrieved from the drawing memory  40  is a transfer instruction. If the retrieved drawing command is a transfer instruction, the process proceeds to step S 81 . Otherwise, the process proceeds to step S 80 .  
         [0092]    In step S 80 , the drawing section  32  determines whether or not the drawing has been completed. If it is determined that the drawing has been completed, that is, if a drawing end instruction has been received, or if all the drawing commands transferred have been executed, the drawing section  32  asserts the Done signal DS sent to the DMA controller  34 , and terminates the drawing processing. If it is determined that the drawing has not been completed, the process returns to step S 78 .  
         [0093]    In step S 81 , the drawing section  32  asserts the Done signal DS sent to the CPU interface  31 . On receipt of the Done signal DS, the CPU interface  31  sets the next drawing command address information in the control register  35 . The process returns to step S 71  for execution of DMA transfer and drawing processing for the new drawing commands.  
         [0094]    As described above, this alteration uses the data transfer management region that manages the data transfer by indicating that the DMA transfer instructed by the host CPU has been completed. This makes it possible to overwrite the region of the main memory  20  from which the drawing commands have been read with new drawing commands. Therefore, undue increase of the capacity of the main memory is prevented and thus the cost can be reduced. In addition, if the data transfer management section is placed at a position permitting poling from the host CPU, the timing of start of next data transfer to the drawing processing unit and the timing of transfer of data to the main memory can be make known.  
         [0095]    Embodiment 2  
         [0096]    [0096]FIG. 9 is a block diagram of a data processor of Embodiment 2 of the present invention. The data processor of FIG. 9 includes a host CPU  210 , a main memory  20 , a drawing processing unit  230 , a drawing memory  40 , a main bus  5 , an I/O block  6  and a DVD-ROM  7 . The host CPU  210  corresponds to the host CPU  10  in FIG. 1. The same components as those of the data processor of FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted here.  
         [0097]    The drawing processing unit  230  includes a CPU interface  231 , a drawing section  232  for actually performing drawing processing, and a memory interface  233 . The CPU interface  231 , functioning as an interface with the main bus  5 , includes a DMA controller  234 . The DMA controller  234  includes a control register  235  for holding parameters required for DMA transfer, and controls data transfer between the main memory  20  and the drawing processing unit  230 . The DMA controller  234  also outputs an interrupt signal IS to the host CPU  210  depending on the transfer state. The drawing section  232  and the memory interface  233  correspond to the drawing section  32  and the memory interface  33  in FIG. 1, respectively. The CPU interface  231  and the memory interface  233  constitute an interface section  239 .  
         [0098]    [0098]FIGS. 10 and 11 are flowcharts of processing by the data processor of FIG. 9, in which FIG. 10 shows processing related to the host CPU  210  and FIG. 11 shows processing related to the drawing processing unit  230 .  
         [0099]    [0099]FIG. 12 illustrates an example of parameters held by the control register  235  shown in FIG. 9. The control register  235  holds an interrupt permit flag in addition to the parameters held by the control register  35  of FIG. 4. The flow of processing by the data processor of FIG. 9 will be described with reference to FIGS.  9  to  12 .  
         [0100]    Processing in steps S 211  to S 213  is substantially the same as that in steps S 31  to S 33  described with reference to FIG. 6, and thus description thereof is omitted here.  
         [0101]    In step S 214 , the host CPU  210  sets the interrupt permit flag, indicating whether or not the drawing processing unit  230  is permitted to generate an interrupt, in the control register  235  of the drawing processing unit  230 , in addition to the head address of the drawing commands in the main memory  20 , the number of words stored, and the destination address in the drawing memory  240  as the destination. The interrupt permit flag is used to notify the host CPU  210  of termination of data transfer related to the set parameters by means of an interrupt when the data transfer is terminated.  
         [0102]    In step S 215 , the host CPU  210  determines whether or not it is necessary to generate drawing commands intended to be transferred next. If necessary, the process proceeds to step S 216 . Otherwise, the process proceeds to step S 217 , where the host CPU  210  terminates processing related to drawing and performs other processing.  
         [0103]    In step S 216 , the host CPU  210  prepares the next drawing commands in the drawing command region of the main memory  20 , and the process returns to step S 215 . The address in the main memory  20  at which the host CPU  210  stores the next drawing commands must be in a region totally irrelevant to the previous transfer. The host CPU  210  repeats the processing in steps S 215  and S 216  until there is no need to generate drawing commands intended to be transferred next.  
         [0104]    Processing in steps S 231  to S 238  in FIG. 11 is substantially the same as the processing in steps S 71  to S 78  described with reference to FIG. 8, and thus the description thereof is omitted here. In step S 239 , when the drawing section  232  receives a drawing end instruction or determines that all transferred drawing commands have been processed, the drawing section  232  outputs the Done signal DS to the DMA controller  234  to complete the drawing processing and waits for input of a new drawing commands.  
         [0105]    After completion of data transfer from the main memory in step S 236 , the DMA controller  234  examines the interrupt permit flag in the control register  235  set by the host CPU  210  in step S 241 .  
         [0106]    If the interrupt permit flag is in the asserted state, the DMA controller  234  generates and outputs the interrupt signal IS to the host CPU  210 , and then negates the interrupt permit flag in step S 242 . The host CPU  210  uses the timing of the interrupt signal IS as the timing at which the next data is transferred or generated, thereby transferring the next drawing data to the main memory  20  or generating drawing data to be next transferred.  
         [0107]    In step S 221  in FIG. 10, the host CPU  210  determines whether or not it is necessary to generate drawing commands intended to be transferred next. If necessary, the process proceeds to step S 222 . Otherwise, the interrupt processing is terminated, and the original processing resumes. In step S 222 , the host CPU  210  prepares the next drawing commands in the region of the main memory  20  in which the drawing commands have already been read. In step S 223 , the host CPU  210  updates data in the control register  235 .  
         [0108]    In the above description, the interrupt was generated upon termination of the transfer. Alternatively, an interrupt may be generated on the following occasion, for example. That is, when preparing data in the main memory  20 , the host CPU  210  may insert an interrupt instruction at a position immediately after certain data at which notification of completion of data transfer so far is necessary. The DMA controller  234  predecodes advanced instructions in drawing data, such as line drawing and filling-in of an area, while transferring the data to the drawing memory  240  or to the drawing section  232 . Therefore, when the DMA controller  234  decodes an interrupt instruction, it can generate an interrupt for the host CPU  210  to notify the host CPU  210  of the progress of the transfer.  
         [0109]    As described above, by being timely notified of the transfer state, the host CPU can determine the timing at which the next data transfer to the drawing processing unit is started and the timing at which data into the main memory is prepared without delay behind the processing by the drawing processing section.  
         [0110]    Embodiment 3  
         [0111]    [0111]FIG. 13 is a block diagram of a data processor of Embodiment 3 of the present invention. The data processor of FIG. 13 includes a host CPU  310 , a main memory  20 , a drawing processing unit  330 , a drawing memory  40 , a main bus  5 , an I/O block  6  and a DVD-ROM  7 . The host CPU  310  corresponds to the host CPU  10  in FIG. 1. The same components as those of the data processor of FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted here. The data processor of FIG. 13 has a feature that a data transfer wait register is used for control of DMA transfer.  
         [0112]    The drawing processing unit  330  includes a CPU interface  331 , a drawing section  332  for actually performing drawing processing, and a memory interface  333 . The CPU interface  331 , functioning as an interface with the main bus  5 , includes a DMA controller  334 . The DMA controller  334  includes a control register  335  for holding parameters required for DMA transfer, and controls data transfer between the main memory  20  and the drawing processing unit  330 . The DMA controller  334  also receives a transfer wait signal TW from the host CPU  310 . The drawing section  332  and the memory interface  333  correspond to the drawing section  32  and the memory interface  33  in FIG. 1, respectively. The CPU interface  331  and the memory interface  333  constitute an interface section  339 .  
         [0113]    [0113]FIG. 14 illustrates an example of parameters held by the control register  335  shown in FIG. 13. As shown in FIG. 14, the control register  335  holds a data transfer wait flag, in addition to the parameters held by the control register  35  of FIG. 4, to thereby additionally function as a data transfer wait register. The host CPU  310  asserts the transfer wait signal TW when it intends to halt DMA transfer temporarily, and sets the data transfer wait flag. In the aspects other than that described above, the data processor of this embodiment is the same as that of the data processor of FIG. 1.  
         [0114]    There are cases that data totally different from a drawing command currently under transfer must be transferred before the DMA controller  334  negates the parameter valid flag. Examples of such cases are that a screen being scrolled rightward is suddenly scrolled downward, and that the host CPU  310  itself intends to generate image data and directly write the data into the frame region of the drawing memory  40 . In such cases, the data processor of FIG. 13 can halt the current transfer temporarily, set new next drawing command address information, and newly transfer a drawing command or image data.  
         [0115]    In the change of the transfer, if two channels of the control register  335  are provided, it is possible to skip data in the main memory  20  of which transfer is no more necessary and restart the data transfer from valid data. For example, if the host CPU  310  intends to transfer image data directly, parameters for transfer of normal map data may be held by one control register while parameters for transfer of image data may be held by the other control register.  
         [0116]    Similar waste-avoiding transfer is possible when data to be processed is stream data, that is, data stored consecutively in the order of processing and processed sequentially. That is, if only the host CPU stores data in the main memory with no overlap of addresses, continuous data transfer is possible based on address information for next transfer by skipping an unnecessary region even when the data is not stored in succession.  
         [0117]    Embodiment 4  
         [0118]    [0118]FIG. 15 is a block diagram of a data processor of Embodiment 4 of the present invention. The data processor of FIG. 15 is the same as the data processor of FIG. 1 except that a drawing processing unit  430  replaces the drawing processing unit  30  in FIG. 1. In FIG. 15, the host CPU, the main memory and the like, which are the same as those in FIG. 1, are omitted. The data processor of FIG. 15 controls supply of a clock signal in the drawing processing unit  430 .  
         [0119]    Referring to FIG. 15, the drawing processing unit  430  includes a CPU interface  431 , a drawing section  432  for actually performing drawing processing, and a memory interface  433 . The CPU interface  431  is the same as the CPU interface  31  shown in FIG. 1. The CPU interface  431  and the memory interface  433  constitute an interface section  439 . The drawing section  432  includes a circuit for dot drawing (dot drawing data path), a circuit for line drawing (line drawing data path), and a circuit for polygon drawing (polygon drawing data path). The memory interface  433  includes a prefetch section  436 , a predecoder  437  and a clock controller  438 .  
         [0120]    [0120]FIG. 16 illustrates an example of drawing commands received by the prefetch section  436  in FIG. 15. In FIG. 16, the prefix “OX” indicates that the subsequent value is in the hexadecimal notation.  
         [0121]    Each of drawing commands such as DOT (dot drawing), POLYGON (polygon drawing) and LINE (line drawing) includes a first control field indicating start of the command located at the head of the command and a second control field indicating end of the command located at the end of the command. Each of the control fields is 8-bit wide, for example, with the four lower-order bits representing the type of the command and the four higher-order bits representing start or end of the command. For example, DOT command includes the first control field, the X coordinate, the Y coordinate and the second control field in this order.  
         [0122]    The prefetch section  436 , which is an interface with the drawing memory  40 , prefetches a drawing command when the drawing command is newly transferred from the drawing memory  40  to the drawing section  432 . The predecoder  437  predecodes the control fields of the drawing command temporarily held by the prefetch section  436 . The clock controller  438  controls supply of a clock signal to the drawing section  432  according to the predecoding result outputted from the predecoder  437 .  
         [0123]    More specifically, the clock controller  438  supplies the clock signal only to one of the circuits of the drawing section  432  corresponding to the type of the drawing command that actually requires the clock signal for the processing of the drawing command. The clock controller  438  starts supply of the clock signal according to the first control field at the start of the command and halts the supply of the clock signal according to the second control field at the end of the command. As for the halt of supply of the clock signal, the predecoder  437  instructs the clock controller  438  to halt supply of the clock signal after waiting for a time period corresponding to the number of cycles required for the drawing section  432  to perform halt processing.  
         [0124]    As described above, only necessary part of the drawing section  432  receives the clock signal. This contributes to reduction in power consumption. In the example shown in FIG. 16, each of the drawing commands DOT, POLYGON and LINE is transferred singly. When a succession of commands of one type, such as a succession of DOT commands, are transferred, however, the control field indicating end of the command for halting supply of the clock signal may be put only at the end of the succession of DOT commands.  
         [0125]    [0125]FIG. 17 diagrammatically illustrates an example of control of supply of a clock signal without use of the predecoder. In this example, the control fields of the drawing commands have bit fields corresponding to the types of the commands and the like. Specifically, as shown in FIG. 17, the control fields have 1-bit fields E, P, L and D associated with the data paths of the drawing section  432 .  
         [0126]    The bit fields E, P, L and D are asserted when the command is a command other than drawing, a POLYGON drawing type command, a LINE drawing type command and a DOT drawing type command, respectively. The clock controller  438  receives the bit fields E, P, L and D from the prefetch section  436 , and supplies the clock signal CL to the dot drawing data path when bit field D is asserted, or to the polygon drawing data path when bit field P is asserted, for example.  
         [0127]    The clock controller  438  includes latches  438 A,  438 B,  438 C and  438 D for latching the bit fields E, P, L and D, respectively. Therefore, the clock controller  438  can continue supply of the clock signal CL to the same data path until a new control field is sent.  
         [0128]    As described above, it is possible to detect to which data path the clock signal should be supplied without the necessity of decoding. Therefore, reduction in power consumption is possible by controlling supply of the clock signal without use of a predecoder.  
         [0129]    Embodiment 5  
         [0130]    [0130]FIG. 18 is a block diagram of a data processor of Embodiment 5 of the present invention. The data processor of FIG. 18 is the same as the data processor of FIG. 1 except that a drawing processing unit  530  replaces the drawing processing unit  30  in FIG. 1. In FIG. 18, the host CPU, the main memory and the like, which are the same as those in FIG. 1, are omitted. In the data processor of FIG. 18, the drawing processing unit  530  makes a notification of termination of processing when the drawing processing unit  530  terminates the processing, to halt unnecessary supply of a clock signal.  
         [0131]    Referring to FIG. 18, the drawing processing unit  530  includes a CPU interface  531 , a drawing section  532  for actually performing drawing processing, and a memory interface  533 . The CPU interface  531  is the same as the CPU interface  31  shown in FIG. 1. The CPU interface  531  and the memory interface  533  constitute an interface section  539 . The configuration of the drawing commands is roughly the same as that described with reference to FIG. 16, except that in this embodiment, each command has no second control field.  
         [0132]    [0132]FIG. 19 is a block diagram of an example of details of the drawing section  532  and the memory interface  533  in FIG. 18. The drawing section  532  includes a dot drawing block  581 , a line drawing block  582  and a polygon drawing block  583 . The dot drawing block  581  includes a dot drawing data path  581 A and a dot drawing controller  581 B. The line drawing block  582  includes a line drawing data path  582 A and a line drawing controller  582 B. The polygon drawing block  583  includes a polygon drawing data path  583 A and a polygon drawing controller  583 B. The memory interface  533  includes a prefetch section  536 , a predecoder  537  and a clock controller  538 .  
         [0133]    The prefetch section  536  and the predecoder  537  operate in substantially the same manner as the prefetch section  436  and the predecoder  437  shown in FIG. 15. The clock controller  538  controls supply of a clock signal to the drawing blocks  581  to  583  according to the predecoding result outputted from the predecoder  537 .  
         [0134]    The clock controller  538  includes flipflops corresponding to the types of the drawing commands, and provides the predecoding result to the flipflops as an enable signal. As a result, the clock controller  538  sends the clock signal only to a block among the drawing blocks  581  to  583  corresponding to the type of the drawing command that actually requires the clock signal for the processing of the drawing command. The clock controller  538  starts supply of the clock signal according to the first control field at the start of the command.  
         [0135]    Assume, for example, that the clock controller  538  selects the polygon drawing block  583  and is supplying the clock signal to the polygon drawing block  583 . Once the drawing processing in the polygon drawing block is terminated, the polygon drawing controller  583 B outputs a drawing done signal DD to the memory interface  533 . On receipt of the drawing done signal DD, the corresponding flipflop is reset, and thus the clock controller  538  halts the supply of the clock signal to the polygon drawing block  583 .  
         [0136]    In the memory interface  533 , the predecoder  536  predecodes data to be transferred next. The clock controller  538  selects the destination of supply of the clock signal according to the predecoding result, and supplies the clock signal to the selected drawing block for execution of drawing.  
         [0137]    In this embodiment, the drawing blocks of the drawing section as the destination of supply of the clock signal themselves can determine halt of supply of the clock signal. Therefore, the clock controller  538  is relieved of considering the timing of halt of supply of the clock signal and the like, and yet reduction in power consumption is possible. In addition, it is possible to control the supply of the clock signal not only to the data paths, but also to the drawing controller controlling the data paths. This further reduces power consumption.  
         [0138]    The predecoder may not be used, and the supply of the clock signal may be started in the manner described above with reference to FIG. 17 and halted upon receipt of the drawing done signal DD.  
         [0139]    In the embodiments described above, the data processor executed drawing as an example of operation by processing drawing commands as operation data. The present invention is also applicable to data processors for performing other operations.  
         [0140]    In the embodiments described above, drawing commands transferred from the main bus to the drawing memory were then transferred to the drawing section for drawing execution. Alternatively, drawing commands may be directly transferred from the main bus to the drawing section for drawing execution. In this case, in Embodiments 4 and 5, the CPU interface, not the memory interface, may be provided with the prefetch section, the clock controller and the like for control of the clock signal.  
         [0141]    While the present invention has been described in a preferred embodiment, it will be apparent to those skilled in the art that the disclosed invention may be modified in numerous ways and may assume many embodiments other than that specifically set out and described above. Accordingly, it is intended by the appended claims to cover all modifications of the invention which fall within the true spirit and scope of the invention.