Abstract:
A processing of data in cooperation with a memory (MEM), for example an MPEG decoding, has the following characteristic features. A processor (P) generates a logic request (LRQ). The logic request (LRQ) defines at least one characteristic (CAR) common to a group of data (GRP). An addressing circuit (AGA) generates a physical request (PRQ) on the basis of the logic request (LRQ). The physical request (PRQ) defines memory (MEM) addresses (A) relating to the group of data (GRP). A memory interface (INT) effects a transfer (TRNSFR) of the group of data (GRP) between the memory (MEM) and the processor (P) on the basis of the physical request (PRQ). Thus, the processor need not know how and where the data to be processed or having been processed are stored in the memory. This facilitates the design of a data processing device and, particularly, a family of such devices.

Description:
FIELD OF THE INVENTION 
     The invention relates to data processing in cooperation with a memory and to addressing of the memory for this purpose. The invention can be used, for example, in an MPEG decoder (MPEG is an acronym for Motion Picture Expert Group). 
     BACKGROUND OF THE INVENTION 
     A processor can access a memory via a memory interface in order to read data to be processed or to write data that has been processed. The processor can transmit an internal address to the memory interface. By means of this internal address the memory interface generates appropriate control signals for the memory. These control signals activate a specific memory cell corresponding to the internal address. 
     By way of example, it is assumed that the internal address comprises 18 bits A[ 17 : 0 ]. For a memory of the DRAM-FPM type the memory interface generates a page number from the 9 more significant bits A[ 17 : 9 ] and a column number from the 9 less significant bits A[ 8 : 0 ]. For a memory of the SRAM type the memory interface generates a bank selection from the fifth bit A[ 5 ] after the least significant bit, a page number from six more significant bits A[  17 : 18 ] and the sixth bit A[ 6 ] after the least significant bit, an even/odd selection from the seventh bit A[ 7 ] after the least significant last bit, and a 64-bit word selection from the five less significant bits A[ 4 : 0 ]. 
     Owing to the memory interface as described hereinbefore, a processor uses always the same communication mode, the internal address, independently of the type of memory used: DRAM-FPM or SDRAM. Such a data processing in cooperation with a memory appears to have been disclosed in the European Patent Application published under the number 0 793 390. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to facilitate the design of a device for data processing in cooperation with a memory. 
     The invention takes into consideration the following aspects. One means of facilitating the design is to ensure that a device can use one or more processors which have already been designed for one or more other devices. The devices may be different, for example, in the sense that they use different memories while they include processors of the same type. Let it be assumed that the devices have an architecture in accordance with the prior art described hereinbefore. In that case it suffices, in principle, to design a memory interface capable of generating, on the basis of an internal address, suitable control signals for the desired memory. Thus, the design should, in principle, only involve the memory interface. 
     However, the following problem may arise when a device is designed on the basis of processors already designed for other devices. It may be preferred that the device to be designed employs a data storage scheme which differs from other devices. A different storage scheme may be preferable for different reasons. For example, the device to be designed may involve a group of processors of a structure which differs from that of other devices. It is advisable to avoid that two processors use the same zone of the memory or that one or more zones are not used. A difference between the device to be designed and the other devices as regards the operating parameters can be another reason for preferring a different storage scheme. For example, let it be assumed that the devices are MPEG decoders. There are different types of MPEG decoding, each type having its own parameters and modes of operation. 
     According to the prior art a different storage scheme implies a different generation of internal addresses. This can only be achieved by modifying the processors. Thus, in accordance with the prior art, the design of a device on the basis of processors already designed for other devices requires a modification of these processors in the case that it is desired that the device to be designed employs a storage scheme which differs from that employed by the other devices. 
     In accordance with the invention a processing of data in cooperation with a memory has the following characteristic features. A processor generates a logic request. The logic request defines at least one characteristic common to a group of data. An addressing circuit generates a physical request on the basis of the logic request. The physical request defines memory addresses relating to the group of data. A memory interface effects a transfer of the group of data between the memory and the processor in response to the physical request. 
     Thus, in accordance with the invention, the processor indicates a certain group of data with the aid of one or more characteristics common to said data. For example, in accordance with the invention, a processor of an image processing device would indicate: “please, provide me with chrominance samples of line  10  of the current image”. The addressing circuit transforms this logic request into a physical request which defines the addresses where the memory stores these samples. Consequently, the processor need not indicate where and how the memory stores these samples. In accordance with the invention, the processor is not affected by the storage scheme and need not be modified in order to enable it to be used in different processing devices using different storage schemes. The invention consequently facilitates the design. 
     The invention will now be described in more detail hereinafter with reference to the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a signal processing device in accordance with the invention; 
     FIG. 2 illustrates the operation of the memory interface of the device; 
     FIG. 3 shows a signal processing unit of the device; 
     FIG. 4 shows the memory interface of the device; 
     FIG. 5 illustrates a read access by a unit; 
     FIGS. 6 a  and  6   b  illustrate an arbitration for access to a collective memory; 
     FIG. 7 shows an access interface of the memory interface; 
     FIG. 8 shows a buffer memory device of the memory interface; 
     FIG. 9 shows a read buffer memory device; 
     FIG. 10 illustrates basic characteristic features of the invention as defined in Claim  1 . 
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following remarks relate to the reference signs. Similar entities bear identical reference letters in all the Figures. A plurality of similar entities may appear in a single Figure. In that case a numeral is suffixed to the reference letters in order to distinguish between similar entities. The numeral or suffix may be omitted for convenience. This applies both to the description and to the Claims. 
     FIG. 1 shows a signal processing device. The device comprise a collective memory SDRAM, a memory interface INT, and three signal processing units B 1 , B 2  and B 3 . These signal processing units will be referred to hereinafter as “units”. Each unit B is connected to the memory interface INT via a private read bus BBR and a private write bus BBW. Each private read bus BBR and each private write bus BBW is dedicated to a given unit B. The memory interface INT is connected to the collective memory SDRAM via a collective bus BM. 
     The general operation of the signal processing device is as follows. On request the units B receive data to be processed, stored in the collective memory SDRAM. After having processed said data the units B apply the processed data to the collective memory SDRAM via the memory interface INT. The memory interface INT controls the access to the collective memory SDRAM by the various units B. 
     The memory interface INT has two basic functions. First of all, it performs an arbitration between the various units B at the level of access to the collective memory SDRAM. A single unit B can access the collective memory SDRAM either for reading or writing at one time. This means that a unit B can access the memory only in a burst mode. Secondly, in the case of reading, the memory interface INT transforms the data bursts coming from the collective memory SDRAM and intended for a given unit B into a substantially steady data stream. This data stream is thus transferred to the unit B via the respective private read bus BBR. In the case of writing the memory interface INT transforms a substantially steady data stream coming from a given unit B into data bursts to be written into the collective memory SDRAM. 
     FIG. 2 illustrates the operation of the memory interface INT. T(BM) represents a data transfer between the collective memory SDRAM and the memory interface INT via the collective bus BM. T(BBR 1 ), T(BBR 2 ) and T(BBR 3 ) represent data transfers between the memory interface INT and the units B 1 , B 2  and B 3 , respectively, via the respective private read buses BBR 1 , BBR 2  and BBR 3 . T(BBW 1 ), T(BBW 2 ) and T(BBW 3 ) represent data transfers between the memory interface INT and the units B 1 , B 2  and B 3 , respectively, via the respective private write buses BBW 1 , BBW 2  and BBW 3 . 
     The data transfer T(BM) consists of data bursts DB. Each data burst DB corresponds to one access operation of the collective memory SDRAM by a unit B either in the write mode or in the read mode. The parenthesized references following DB indicate to which unit B the data in the burst belong and also indicate the type of access: write (W) or read (R). For example, DB 1 (B 1 /R) indicates that the data burst DB 1  concerns an access to the collective memory SDRAM in the read mode by B 1 . 
     FIG. 2 shows that the memory interface INT performs a “smoothing” of the data bursts coming from the collective memory SDRAM and belonging to a certain unit B. This Figure also shows that, conversely, the memory interface INT performs a time concentration of the data received from a unit B in order to write said data into the collective memory SDRAM as a burst (data compression). Thus, the transfers of data via the private read buses BBR and the private write buses BBW are effected at comparatively low rates. Consequently, this makes it possible for the private read buses BBR and the private write buses BBW to have comparatively narrow pass bands and, as a result, to have a comparatively small width. In this respect it is to be noted that the size of a bus need not necessarily correspond to the number of bits contained in the data transferred by this bus. For example, 16 bit data can be split into 4 bit words. Thus, said data can be transferred via a 4 bit bus in the form of a sequence of 4 words. 
     FIG. 3 shows a unit B. The unit B comprises a processor P and a general addressing circuit AGA. The processor P makes logic requests LRQ. It is assumed that the unit B processes video data, in which case a logic request LRQ may be, for example, a request for pixels of a given line in the current image. The general addressing circuit AGA transforms the logic request LRQ into a physical request PRQ. The physical request PRQ defines the physical addresses where the requested data is stored in the collective memory SDRAM. The physical requests PRQ may have the following form: a start address, a number of addresses to be searched starting from said address and, if applicable, a scheme to be employed during the search for data. This schema may be defined in the form of: the number of consecutive addresses to be read, the number of addresses to be jumped and the number of “read and jump” iterations. The AGA may be programmable in such a manner that translation parameters define the translations of logic requests LRQ into physical requests PRQ. This enables a flexible storage of data into the collective memory SDRAM. 
     FIG. 4 shows the memory interface INT. The memory interface INT comprises an arbiter ARB, an access interface SIF, a buffer memory device BUF and addressing and macro-command circuits AGB. There is an addressing and macro-command circuit AGB for each unit B. 
     On the whole, the internal operation of the memory interface INT is as follows. Each addressing and macro-command circuit AGB divides a physical request from the unit B with which it is associated into macro-commands. A macro-command represents a request for access to a given row in the memory. Before a macro-command is submitted to the arbiter ARB the addressing and macro-command circuit AGB verifies whether there is enough room in the buffer memory device BUF. To this end, it first applies the macro-command to the buffer memory device BUF. If the buffer memory device BUF confirms that there is room for the storage of the number of data defined by the macro-command, the addressing and macro-command circuit AGB submits the macro-command to the arbiter ARB. The arbiter ARB receives the macro-commands from the various addressing and macro-command circuits AGB and selects a macro-command to be applied to the access interface SIF. This selection is made in accordance with an arbitration scheme described hereinafter. The access interface SIF processes the macro-commands received from the arbiter ARB in the order of their receipt. Thus, the access interface SIF provides the access to the collective memory SDRAM, the access operations being defined by the macro-command being processed. 
     A macro-command enables X groups of addresses to be accessed, each group comprising Y addresses, the groups of addresses being separated from one another by Z words, X, Y and Z being integers. Thus, a macro-command contains the following information: 
     first address to be accessed; 
     number of addresses to be accessed following upon the first address in a group of addresses (Y-1); 
     number of addresses to be skipped between two groups of consecutive addresses (Z); 
     number of address groups to be accessed in addition to the first group (X-1); 
     type of access: read or write. 
     An example of a macro-command at bit level is as follows. It is assumed that the data stored in the collective memory SDRAM has a width of 32 bits and the collective memory SDRAM has a maximum capacity of 256 Megabit. This means that an address is expressed as 23 bits. It is further assumed that the access operations are limited to a maximum size of 16 addresses. Such a limit is preferred in view of latency. Thus, X-1 and Y1 are 15 at the most and can consequently be coded in 4 bits. Finally, a row contains a maximum of 512 addresses in accordance with the configuration of the collective memory SDRAM. Consequently, the number of addresses to be jumped cannot exceed 511 and, as a result, this number can be coded in 9 bits. The macro-commands thus have a size of 23+2×4+9+1=41 bits. The address can be coded in the bits  40  to  18 , the access type in the bit  17 , the number of words to be read (Y-1) in the bits  16  to  13 , the number of words to be jumped (Z) in the bits  12  to  4 , and the number of word groups (X-1) in the bits  3  to  0 . 
     FIG. 5 illustrates a process of access to the collective memory SDRAM in the read mode by a given unit B. The horizontal dimension represents the time. The vertical dimension of this diagram represents the different functional elements which are involved. The diagram contains arrows. These arrows represents various steps S in the process of access to the interface memory SRAM. 
     S1=The processor P of the relevant unit B submits a logic request LRQ to the general addressing circuit AGA. The logic request LRQ specifies a data sub-set, for example the luminance pixels of a line in a set of data to be processed, for example an image. 
     S2=The general addressing circuit AGA transforms the logic request LRQ into a physical request PRQ. 
     S3=The general addressing circuit AGA submits the physical request PRQ to the macro-commands addressing circuit AGB. 
     S4=The macro-command addressing circuit AGB transforms the physical request PRQ into macro-commands. 
     S5=The macro-command addressing circuit AGB submits the first one of the macro-commands derived from the physical request PRQ to the buffer memory device BUF. 
     S6=The buffer memory device BUF verifies whether there is room for the storage of the number of data specified by the macro-command. 
     S7=The buffer memory device BUF sends an acknowledgement to the macro-command addressing circuit AGB that there is room. 
     S8=Represents a given delay. 
     S9=The macro-command addressing circuit AGB submits the macro-command to the arbiter ARB. 
     S10=The arbiter ARB processes the macro-command as a request for access to the collective memory SDRAM in accordance with an arbitration schema which applies to any access to the collective memory SDRAM by the units (in the read and in the write mode). 
     S11=The arbiter ARB submits the macro-command to the access interface SIF. 
     S11a =The arbiter ARB sends an acknowledgement to the buffer memory device BUF that the macro-command has been submitted to the access interface SIF. 
     S12=The macro-command is queued in the access interface SIF, which first processes the previously received macro-commands. 
     S13=The access interface SIF generates control signals for the collective memory SDRAM on the basis of the macro-command. These control signals results in the data at the addresses specified by the macro-command are read successively. 
     S14=The data successively read from the collective memory SDRAM is transferred to the buffer memory device BUF. 
     S15=The buffer memory device BUF temporarily stores the data. 
     S16=The buffer memory device BUF transfers the data to the processor P in a substantially steady manner. 
     The steps S5-S15 are repeated for each macro-command following the logic request LRQ made in the step S1. 
     The next steps are not shown in FIG.  5 . Upon the step S1 the general addressing circuit AGA sends an acknowledge signal to the processor P, which signal indicates that the logic request LRQ has been accepted and will be processed. In response to this acknowledge signal the processor P makes a new logic request and holds it till further notice. When the macro-command addressing circuit AGB submits the last macro-command in response to the logic request LRQ the processing of the logic request LRQ is finished. In that case the macro-command addressing circuit AGB sends an acknowledge signal to the general addressing circuit AGA to indicate to the latter that the processing of the logic request LRQ has been completed. In response thereto, the general addressing circuit AGA starts the processing of the new logic request LRQ in a manner similar to the processing of the logic request LRQ effected in the step S1. In other words, the process is repeated. 
     FIGS. 6 a  and  6   b  show an arbitration scheme for the arbiter ARB. In FIG. 6 a  eight states ST 1 -ST 8  are shown as circles. These states ST occur one after the other and in a cyclic fashion. Each state ST represents a possibility of sending a macro-command to the access interface SIF. Thus, each state represents a possibility of accessing a memory. Each state corresponds to a given processor P. The processor P to which a given state corresponds is specified in the circle representing the state. 
     FIG. 6 b  represents the arbitration process corresponding to FIG. 6 a . This process comprises a plurality of steps SA 1 -SA 4  and is carried out for each state ST in FIG. 6 a . The step SA 1  is the first step carried out after a jump of state. In the step SA 1  the arbiter ARB verifies if a macro-command, submitted by the macro-command addressing circuit AGB and following a logic request LRQ from the processor P[j] to which the state S[i] corresponds, is pending. If such a macro-command is pending the step SA 1  is followed by the step SA 2 . In the step SA 2  the arbiter ARB sends the relevant macro-command to the access interface SIF. The effect of this is that after a given delay the collective memory SDRAM will be accessed by the relevant processor P as defined by the macro-command. After the macro-command has been sent the arbiter jumps to the next state, which means that the process represented in FIG. 6 b  is repeated. However, if in the step S1 the arbiter ARB has detected that there is no pending macro-command associated with the processor P to which the state S[i] corresponds, the step SA 1  is followed by the step SA 3 . In the step SA 3  the arbiter ARB verifies if other macro-commands are waiting. If there are no other macro-command waiting the arbiter ARB jumps to the next state and the process shown in FIG. 6 b  is repeated. If there are other macro-commands waiting the arbiter ARB performs the step SA 4 . In the step SA 4  the arbiter ARB selects a macro-command in an order of priority. Each macro-command has a given level of priority. The priority level is determined by the processor P from which the macro-command originates. The arbiter ARB thus selects the macro-command having the highest priority level and sends this macro-command to the access interface SIF. After having sent the macro-command the ARB jumps to the next state, which means that the process shown in FIG. 6 b  is repeated. 
     With regard to FIGS. 6 a  and  6   b  it is to be noted that it is not necessary that each state corresponds to a processor P. It is possible to introduce one or more states which do not correspond to any processor P, which means that it is possible to introduce free states. In the case of a free state the arbiter ARB selects a macro-command only on the basis of the priority order. Such a free state can be useful in the case that the signal processing device includes a processor P whose restraints in terms of latency time and pass band at the level of access to the collective memory SDRAM are comparatively moderate. Thus, in order to avoid that this processor P is not given enough access, free states could be introduced. The processor P can take advantage of these free states to access the collective memory SDRAM. 
     FIG. 7 shows an example of the access interface SIF. The access interface SIF comprises a macro-command buffer memory FIFO_MC, a column generator CAGU, a command generator CGU, a control signal generator IF_SDRAM, a data buffer memory IF_D. 
     The general operation of the access interface SIF is as follows. The macro-command buffer memory FIFO_MC receives the macro-commands from the arbiter ARB. This memory temporarily stores these macro-commands and sends them to the column generator CAGU in the order of their arrival. In the case that the macro-command buffer memory FIFO_MC is full and therefore cannot accept a new macro-command, it reports this to the arbiter ARB. As a result of this signal from the access interface SIF, which indicates that its “FIFO is full”, the arbiter ARB postpones the transfer of the currently selected macro-command until the instant at which the macro-command buffer memory FIFO_MC reports that it can accept a new macro-command. In fact, the “FIFO is full” signal from the access interface SIF “freezes” the arbiter ARB for a certain time. 
     The column generator CAGU requests a new macro-command from the macro-command buffer memory FIFO_MC when the memory access operations in accordance with the preceding macro-command have been carried out. As a matter of fact, the column generator CAGU in combination with the command generator CGU translate the macro-command into a series of addresses. An address of the collective memory SDRAM is defined by the number of a bank of the collective memory SDRAM, the number of a row and the number of a column. It has already been stated that a macro-command relates to an access to a single row of the interface memory SRAM, which automatically implies that the access takes place in a single bank. Therefore, it suffices that the column generator CAGU generates a series of columns on the basis of the macro-command in order to define a series of addresses in accordance with the macro-command. An implementation of the column generator CAGU may comprise, for example, some counters and some logic circuits. In such an implementation the content of a macro-command serves to program the counters. 
     The command generator CGU successively receives another column number of the collective memory SDRAM. The command generator CGU further receives from the macro-command buffer memory FIFO_MC the bank number and the row number of the addresses as defined by the macro-command. This information enables the column generator CAGU to define a series of commands for access to the collective memory SDRAM, each command defining a single address. Moreover, the command generator CGU generates commands necessary for setting the collective memory SDRAM to a correct state so as to allow the access operations as defined by the macro-commands. These commands relate to the appropriate processes for the collective memory SDRAM, such as preloading and activation. Furthermore, the command generator CGU ensures that the collective memory SDRAM is refreshed at regular intervals and generates the commands necessary to perform these refresh operations. 
     The control signal generator IF_SDRAM generates control signals on the basis of the commands received from the command generator CGU. For example, the control signal generator IF_SDRAM generates signals referred to by the acronyms RAS, CAS. The control signal generator IF_SDRAM ensures that in a series of control signals certain waiting times for the collective memory SDRAM are observed. These waiting times may vary depending on the type of collective memory SDRAM that is used. Consequently, the control signal generator IF_SDRAM is specific to the type of collective memory SDRAM that is used. If a collective memory SDRAM of another type is to be used it is sufficient to modify, i.e. reprogram, the control signal generator IF_SDRAM. In principle, the other elements of the access interface do not require any modifications. 
     The data buffer memory IF_D serves to transfer the data from the collective memory SDRAM to the buffer memory shown in FIG. 4 in the case of reading and to transfer the data from the buffer memory BUF to the collective memory SDRAM in the case of writing. For this purpose, the data buffer memory data buffer memory IF_D synchronizes the data supplied by the collective memory SDRAM (reading) or applied to the collective memory SDRAM (writing). Moreover, the data buffer memory IF_D forms a FIFO having a unit depth. This means that if a given clock pulse causes data to be read from the collective memory SDRAM this data will be transferred to the buffer memory device BUF on the next clock pulse. In the case of writing this is the other way round. 
     FIG. 8 shows an example of the buffer memory device BUF which forms part of the memory interface INT shown in FIG.  4 . The buffer memory device BUF comprises a read buffer memory device BUFR as well as a write buffer memory device BUFW and a buffer memory for acknowledge signals FIFO_ACK. The read buffer memory device BUFR and the write buffer memory device BUFW are connected to the collective memory SDRAM via the access interface SIF and the collective bus BM as is shown in FIG.  1 . The read buffer memory device BUFR is connected to the units B 1 , B 2  and B 3  via the private read buses BBR 1 , BBR 2  and BBR 3 , respectively. The write buffer memory device BUFW is connected to the units B 1 , B 3  and B 3  via the private write buses BBW 1 , BBW 2  and BBW 3 , respectively. The acknowledge signal buffer memory FIFO_ACK is connected to the arbiter ARB. 
     The general operation of the buffer memory device BUF is as follows. The read buffer memory device BUFR temporarily stores the data received from the collective memory SDRAM, while the write buffer memory device BUFW stores the data to be written into the collective memory SDRAM and received from the different units B. The acknowledge signal buffer memory FIFO_ACK receives the acknowledge signals coming from the arbiter ARB. Such a signal indicates that the arbiter ARB has applied a macro-command to the access interface SIF. 
     The acknowledge signal buffer memory FIFO_ACK has the same depth as the macro-command buffer memory FIFO_MC of the access interface SIF shown in FIG.  7 . Consequently, when a macro-command leaves the macro-command buffer memory FIFO_MC, as a result of which a memory access in accordance with the macro-command is effected, the acknowledge signal corresponding to this macro-command leaves the acknowledge signal buffer memory FIFO_ACK. This signal indicates whether the relevant access operation is a read access or a write access. In the first-mentioned case the read buffer memory device BUFR is activated to receive data from the collective memory SDRAM, while in the last-mentioned case the write buffer memory device BUFW is activated to send data to the collective memory SDRAM. The acknowledge signal supplied by the acknowledge signal buffer memory FIFO_ACK further indicates the number of data involved in the access operation as defined by the macro-command. This indication is used by the buffer memory device BUF for the internal management of “where to store the data or where to fetch the data?” in the case of reading or writing, respectively. 
     FIG. 9 shows an example of the read buffer memory device BUFR. The read buffer memory device BUFR comprises an input buffer memory IB, an interface memory SRAM, a arrangement comprising a plurality of output buffer memories OB, an arrangement of control circuits CON, and an interface memory access arbiter ARBBR. The input buffer memory IB is connected to the collective memory SDRAM via the access interface SIF already shown in FIG.  4 . The output buffer memories OB 1 , OB 2  and OB 3  are connected to processors P 1 , P 2  and P 3  via the private read buses BBR 1 , BBR 2  and BBR 3 , respectively, the last-mentioned elements being shown in FIGS. 2 and 3. The control circuits CON 1 , CON 2  and CON 3  are connected to the macro-command addressing circuit AGB 1 , the macro-command addressing circuit AGB 2  and the macro-command addressing circuit AGB 3 , respectively, as well as to the access interface SIF. 
     The read buffer memory device BUFR operates as follows. The data received from the collective memory SDRAM has a width of N bits, N being an integer, and arrive with a frequency F. The interface memory SRAM has a width of 2N bits, which means that an address can contain 2N bits, and operates at the frequency F. The input buffer memory IB forms pairs of two consecutive data coming from the collective memory SDRAM and loads these pairs into the interface memory SRAM. It takes two clock cycles to form one pair. When it is assumed that all the successive data received from the collective memory SDRAM can be paired, a write access to the interface memory SRAM will be effected every two clock cycles. Access to a single address requires only one clock cycle. Thus, between two write access operations one clock cycle is available to access the interface memory SRAM for reading, in order to transfer the data read from the collective memory SDRAM to the units B. Thus, in principle, write access and read access to the interface memory SRAM can be effected alternately and one after another. The access to the interface memory SRAM will be described in greater detail hereinafter. 
     The interface memory SRAM is, in fact, divided into three zones Z 1 , Z 2  and Z 3 . The zones Z 1 , Z 2  and Z 3  contain the data intended for the processors P 1 , P 2  and P 3 , respectively. The data from the collective memory SDRAM is written into the zone Z 1 , Z 2  or Z 3  via the IB depending on the processor P from which the current macro-command originates. The data present in the zones Z 1 , Z 2  and Z 3  is transferred to the output buffer memories OB 1 , OB 2  and OB 3 , respectively, in a substantially steady fashion and in accordance with a substantially fixed scheme. An output buffer memory OB in fact splits the data into a plurality of parts and applies the relevant data to the respective processor P part by part. For example, an output buffer memory OB can split 16 bit data into 4-bit parts. Thus, instead of transferring the data in a single clock cycle, which requires a 16-bit bus, the data is transferred part by part in 4 clock cycles, which requires only a 4-bit bus. 
     The control circuits CON 1 , CON 2  and CON 3  control the zones Z 1 , Z 2  and Z 3 , respectively. For this purpose, each control circuit CON controls a group of parameters. These parameters include a write pointer, a read pointer and a zone occupancy value. The write pointer defines the address in which the data from the collective memory SDRAM is to be written. The read pointer defines the address of the data to be transferred to the relevant output buffer memory OB. The occupancy value indicates the number of addresses still available for the storage of the data received from the collective memory SDRAM. The control circuits CON 1 , CON 2  and CON 3  also control the output buffer memories OB 1 , OB 2  and OB 3 , respectively. For this purpose, each control circuit CON controls a parameter representing the state of occupancy of the corresponding output buffer memory OB. 
     The control process carried out by a control circuit CON will now be described, assuming that the collective memory SDRAM is accessed as illustrated in FIG.  5 . In the step S5 the macro-command addressing circuit AGB submits a macro-command to the buffer memory device BUF. This macro-command is processed by the control circuit CON corresponding to the processor P from which the macro-command originates. The control circuit CON compares the number of data defined by the macro-command with the occupancy value. Thus, the control circuit CON verifies whether there is sufficient room in the relevant zone Z to store the desired data. If there is enough room, the control circuit CON reports this to the macro-command addressing circuit AGB and, moreover, updates the occupancy parameter. This means that it considers the data as already stored in the relevant zone while this should still be done. Therefore, the update of the occupancy parameter may be regarded as a reservation in the relevant zone. 
     What happens during the step S12 as shown in FIG. 5 will now be described. This step S12 represents a read-out of the collective memory SDRAM in accordance with the relevant macro-command. It has already been explained that at the instant at which the access interface SIF starts to process the macro-command and thus starts the read-out, the acknowledge signal associated with the relevant macro-command leaves the acknowledge signal buffer memory FIFO_ACK shown in FIG.  7 . This acknowledge signal indicates that the access is a write operation and, moreover, this signal specifies the processor P from which the macro-command stems. Thus, the control circuit CON corresponding to this processor P knows that it should supply the addresses where the data should be stored in the collective memory SDRAM. Furthermore, the control circuit CON receives an indication of the number of data involved in the access operation in accordance with the macro-command, which indication forms part of the acknowledge signal. 
     Each time that a data pair from the collective memory SDRAM is written into the relevant zone Z the control circuit CON increments the write pointer. Moreover, it updates the occupancy value. The control circuit CON continues to do so until the read access to the collective memory SDRAM as defined by the macro-command has been completed. The control circuit CON detects the end of the access operation with the aid of the number of data involved in the access operation, this number being indicated by the acknowledge signal, and a by counting the data written into the interface memory SRAM. 
     After each read-out of a data pair from a given zone Z the control circuit CON which controls this zone increments the read pointer. Moreover, it updates the occupancy value. 
     The interface memory access arbiter ARBBR controls the access to the interface memory SRAM. There are different types of access: (1) access by the access interface SIF to write data from the collective memory SDRAM into the interface memory SRAM, (2) access operations by the output buffer memory OB 1 , (3) access operations by the output buffer memory OB 2 , and (4) access operations by the output buffer memory OB 3 . The three last-mentioned access operations serve to transfer data contained in the interface memory SRAM to the processors P 1 , P 2  and P 3 , respectively. 
     Any access to the interface memory SRAM is effected in response to a request submitted to the interface memory access arbiter ARBBR. From the current requests the interface memory access arbiter ARBBR selects the request having the highest priority. The write access requests (access via the access interface SIF) having the maximal priority. As a result of the fact that pairs of data are written, as explained hereinbefore, such a request generally occurs only once every two clock cycles. A write operation requires only one clock cycle. Consequently, there will be enough opportunities to access the interface memory SRAM in the read mode in order to transfer the data to the various processors P. 
     The read access requests by a given output buffer memory OB are made depending on the size of the private read bus BBR between the output buffer memory OB and the unit B. It is assumed, for example, that the size of the bus is N/2 bits. This means that a N/2 bit part can be transferred from the output buffer memory OB to the unit B in every clock cycle. Reading of the interface memory SRAM is effected in pairs of data. One data pair comprises 2N bits. Therefore, 4 clock cycles are needed to send one data pair to the unit B. The transfer of one data pair involves a request for access to the interface memory SRAM in the read mode. Thus, in the present example, the output buffer memory OB will submit an access request every 4 clock cycles. This example shows that the sizes of the buses to the units B dictate the frequency of the access requests of the various output buffer memories OB. If the size of the private read bus BBR is N/4 bit there will be an access request every 8 clock cycles. 
     The following description relates to an example of arbitration for access to the interface memory SRAM. It is assumed that the size of the private read bus BBR 1  is N/2 bits and that the size of the private read bus BBR 2  and that of the private read bus BBR 3  is N/4 bits. The access operations of the access interface SIF have the highest priority, followed, in order of priority, by the access operations of the output buffer memories OB 1 , OB 2  and OB 3 . Finally, it is assumed that the requests for all the types of access (SIF, OB 1 , OB 2 , OB 3 ) are submitted simultaneously in the first clock cycle. 
     Cycle  1 : all the requests are made at the same time; pending requests: the access interface SIF, the output buffer memories OB 1 , OB 2  and OB 3 . 
     Cycle  2 : the interface access SIF having the highest priority has the lead and drops its request; the output buffer memories OB 1 , OB 2  and OB 3  maintain their requests; pending requests: the output buffer memories OB 1 , OB 2  and OB 3 . 
     Cycle  3 : the output buffer memory OB 1 , which has the second highest priority, has the lead and drops its request; the access interface SIF submits a new request; pending requests: access interface SIF, the output buffer memories OB 2  and OB 3 . 
     Cycle  4 : the access interface SIF having the highest priority has the lead and drops its request; the output buffer memories OB 2  and OB 3  maintain their requests; pending requests: the output buffer memories OB 2  and OB 3 . 
     Cycle  5 : the output buffer memory OB 2 , which has the third highest priority, has the lead and drops its request; the access interface SIF submits a new request; pending requests: the access interface SIF and the output buffer memory OB 3 . 
     Cycle  6 : the access interface SIF having the highest priority has the lead and drops its request; the output buffer memory OB 1  is running out of buffer capacity and again submits a request; pending requests: the access interface SIF, the output buffer memories OB 1  and OB 3 . 
     Cycle  7 : the output buffer memory OB 1 , which has the second highest priority, has the lead and drops its request; the access interface SIF submits a new request; pending requests: the access interface SIF, the output buffer memory OB 3 . 
     Cycle  8 : the access interface SIF having the highest priority has the lead and drops its request; the output buffer memory OB 3  maintains its request; pending request: output buffer memory OB 3 . 
     Cycle  9 : the output buffer memory OB 3 , which has the fourth highest priority, has the lead and drops its request; the access interface SIF submits a new request; pending request: the access interface SIF. 
     Cycle  10 : the access interface SIF having the highest priority has the lead and drops its request; the output buffer memory OB 1  is running out of buffer capacity and again submits a request; pending request: the output buffer memory OB 1 . 
     Cycle  11 : the output buffer memory OB 1 , which has the second highest priority, has the lead and drops its request; the access interface SIF submits a new request; pending request: the access interface SIF. 
     Cycle  12 : the access interface SIF having the highest priority has the lead and drops its request; the output buffer memory OB 2  is running out of buffer capacity and again submits a request; pending request: the output buffer memory OB 2 . 
     Cycle  13 : the output buffer memory OB 2  having the third highest priority has the lead and drops its request; the access interface SIF submits a new request; pending request: the access interface SIF. 
     Cycle  14 : the access interface SIF having the highest priority has the lead and drops its request; the output buffer memory OB 1  is running out of buffer capacity and again submits a request; pending request: the output buffer memory OB 1 . 
     Cycle  15 : the output buffer memory OB 1  having the second highest priority has the lead and drops its request; the access interface SIF submits a new request; pending request: the access interface SIF. 
     Cycle  16 : the access interface SIF having the highest priority has the lead and drops its request; the output buffer memory OB 3  is running out of buffer capacity and again submits a request; pending request: the output buffer memory OB 3 . 
     Cycle  17 : the output buffer memory OB 3  having the fourth highest priority has the lead and drops its request; the access interface SIF submits a new request; pending request: the access interface SIF. 
     Cycle  18 : the access interface SIF having the highest priority has the lead and drops its request; the output buffer memory OB 1  is running out of buffer capacity and again submits a request; pending request: the output buffer memory OB 1 . 
     Cycle  19 : the output buffer memory OB 1  having the second highest priority has the lead and drops its request; the access interface SIF submits a new request; pending request: the access interface SIF. 
     Cycle  20 : the access interface SIF having the highest priority has the lead and drops its request; the output buffer memory OB 2  is running out of buffer capacity and again submits a request; pending request: the output buffer memory OB 2 . 
     Cycle  21 : the output buffer memory OB 2  having the third highest priority has the lead and drops its request; the access interface SIF submits a new request; pending request: the access interface SIF. 
     Cycle  22 : the access interface SIF having the highest priority has the lead and drops its request; the output buffer memory OB 1  is running out of buffer capacity and again submits a request; pending request: the output buffer memory OB 1 . 
     Cycle  23 : the output buffer memory OB 1  having the second highest priority has the lead and drops its request; the access interface SIF submits a new request; pending request: the access interface SIF. 
     Cycle  24 : the access interface SIF having the highest priority has the lead and drops its request; the output buffer memory OB 3  is running out of buffer capacity and again submits a request; pending request: the output buffer memory OB 3 . 
     Cycle  25 : the output buffer memory OB 3  having the fourth highest priority has the lead and drops its request; the access interface SIF submits a new request; pending request: the access interface SIF. 
     Cycle  26 : the access interface SIF having the highest priority has the lead and drops its request; the output buffer memory OB 1  is running out of buffer capacity and again submits a request; pending request: the output buffer memory OB 1 ; 
     Etc. 
     The access operations described hereinbefore have a periodicity of 8 cycles. It is as though arbitration is effected by a cyclic machine having eight states. This is owing to the fact that in the example it is assumed that all the units B process their data in a regular fashion. Moreover, it is assumed that the access requests by the access interface SIF are submitted regularly once every two clock cycles. In practice, these assumptions are not necessarily correct. For this reason, it is preferred to control the access to the interface memory SRAM with the aid of an arbiter and in an order of priority rather than with the aid of a cyclic machine. The arbiter allows a certain degree of flexibility as regards the access to the interface memory SRAM and, consequently, it allows a better utilization of the bandwidth available for the data transfer. 
     The following is an example of an exception to the rule in accordance with which there is only one write access to the interface memory SRAM (=access by the access interface SIF) every two clock cycles. This exception occurs in the case of an access to the collective memory SDRAM in response to a macro-command involving an odd number of data. All the data involved in this access, except for the last data element, have a partner and thus form pairs to be written into the interface memory SRAM. The last data element is alone. It is not possible to use the next data element to form a pair because this data element is the first data element of another access operation and is therefore intended for another processor P. As a result, this first data element of another access operation should be stored in another zone Z of the interface memory SRAM. Thus, upon the arrival in the IB of the last data element of the access involving an odd number of data elements said data is loaded into the interface memory SRAM without a partner in the clock cycle that follows the write operation for the last data pair comprised in the access operation. Consequently, there will be two write access operations in succession without a break of one clock cycle, which would otherwise allow a read access operation between two write access operations. 
     FIGS. 5 and 9 relate to the operation of the memory interface INT in the read mode. The operation in the write mode is substantially symmetrical. This means that the write buffer memory device BUFW is similar to the read buffer memory device BUFR described hereinbefore. Thus, the write buffer memory device BUFW comprises an interface memory divided into zones, each zone being associated with a different unit B. The units B can supply data to be written into the collective memory before or after the macro-command which indicates where this data should be stored. In fact, a zone will be filled as soon as the unit B to which the zone corresponds supplies data to be stored in the collective memory. Said filling may continue, for example, until the zone is completely filled with data. In this case the memory interface INT will indicate to the relevant unit B that there is no longer any room for the storage of new data. This will prevent the unit B from supplying new data until room has become available in the relevant zone. A data transfer from the zone Z to the collective memory results in room being made available. Such a dump can occur as soon as a macro-command is accepted by the arbiter ARB and is processed by the access interface SIF. It is likewise possible that a macro-command is issued before the relevant unit B has supplied the data. In any case, no macro-command will be applied to the arbiter ARB as long as the write buffer memory device BUFW does not indicate an adequate filling level of the relevant zone. 
     FIG. 10 illustrates basic characteristic features of the invention as outlined in the section “Summary of the invention”. A processor P generates a logic request LRQ. The logic request LRQ defines at least one characteristic CAR common to a group of data FRP. An addressing circuit AGA generates a physical request PRQ on the basis of the logic request LRQ. The physical request PRQ defines addresses A of the memory MEM relating to the group of data GRP. A memory interface INT effects a transfer TRNSFR of said group of data GRP between the memory MEM and the processor P in response to the physical request PRQ. 
     The characteristics illustrated in FIG. 10 may be used, for example, in a video processing device. In this case the logic request LRQ may define, for example, a line of luminance pixels. Such a request can be made by, for example, by a processor for carrying out processing operations for the display. A logic request will generally be adapted to the processor from which it comes. The logic requests may therefore have profiles which differ greatly from one processor to the other. However, it is possible to standardize, for example, a protocol for the exchange of parameters as, for example, the line number and the pixel type: luminance or chrominance. The addressing circuit AGA will generally have the task of storing the storage parameters, the memory type, one or more addresses where the data storage starts. This storage can be effected in conjunction with a central processing unit (CPU). 
     The above Figures and their description illustrate rather than limit the invention. It is evident that there are numerous alternatives within the scope of the appended Claims. In conclusion, some remarks are made in this respect. 
     The functional entities or functions can be allocated in many different ways. In this respect, it is to be noted that the Figures are highly diagrammatic, each Figure representing merely a single embodiment of the invention. Thus, although a Figure shows different functional entities as separate blocks, this does not exclude the fact that a plurality of functional entities are presented as a single physical entity. 
     Finally, any reference signs given in parentheses in a Claim shall not be construed as limiting said Claim. The use of the verb “to comprise” does not exclude the presence of elements or steps other than those defined in a Claim. The use of the indefinite article “a” preceding an element or step does not exclude the presence of a plurality of these elements or steps.