External memory control device

Abstract: An external memory control device, which is capable of reducing the time required for processing the writing and reading of data for the storage areas of an external memory device. The external memory control device includes a smallest sector number register and a largest sector number register which stores the smallest and the largest sector numbers, respectively, within a processing range that is designated by the track of a processing request signal from the central processing unit. A processing range detecting part detects whether the sector number read from the designated track is within the processing range, and means which stores, when the sector number read first from the designated track is within the processing range. The following sector number in the sector number register. Stores the smallest sector number when the sector number is outside the processing region and generates a discrimination signal which is turned on when the sector number read out and the sector number which is the stored contents of the sector number register coincide, and updates the stored contents of the sector number register to the next sector number. In this external memory control device, if the sector number read from the designated track is within the processing range, the processing start from the next sector, so that the holding of the operation until the arrival of the smallest sector number is no longer needed, and the time required for processing per track can be reduced.

Description: Field of the Invention The present invention relates to a control device which controls an external memory device of a computer system, and more particularly, to a control device of this kind which stores a minimum unit write or read data in a unit storage area together with identification information. Description of the Prior Art A control device which controls an external memory device is provided between a host system, namely, a CPU and the external memory device, and performs the control for writing of a data to the external memory device, reading of a data from the external memory device, and the like under the control of the host system. In a magnetic disk device which is a representative external memory device, a unit storage area on a magnetic disk for storing a smallest unit of write or read data is called a sector, and identification information proper to a sector and a smallest unit data are stored in the sector. Identification information is constituted of a head number which specifies a magnetic head that is capable of accessing the storage surface to which the sectors belong, a track number which specifies each track on the storage surface, and a sector number given to a large number of sectors contained in each of the tracks. In writing or reading a data of the smallest unit (referred to as a unit data hereinafter), a magnetic disk control device first selects the magnetic head and the track corresponding to a sector designated by the host system, and instructs the magnetic disk device so as to read the sector identification information from the designated sector by driving the magnetic head to the selected track. The magnetic disk control device discriminates whether or not the sector number among the sector identification information that was read out coincide with the sector number designated by the host system, and carries out a processing such as write or read of a unit data to the sector if they coincide with each other and controls the magnetic disk device so as to read the identification information of the adjacent sector if they do not coincide. In the magnetic disk device, write or read of a unit data is ordinarily carried out for a plurality of sectors of at least one track by one request for processing. In the prior art magnetic disk control device, first, the sector number of the starting point of a processing such as writing or reading (referred to as a processing hereinafter) for the track is stored in a first register and the number of sectors to be processed or the sector number of the completion point of the processing is stored in a second register. If the sector number that is read out and the stored contents of the first register, that is, the sector number of the starting point of the processing is found to be coincident with each other upon comparison, the magnetic disk device is controlled so as to read the sector number of the next sector after performing the processing for that sector, and the stored contents of the first register is updated to the sector number of the next sector. Further, if the stored contents of the second register is the number of sectors of the objects to be processed, the number is decremented by one. If the sector number that is read out does not coincide with the stored contents of the first register, the magnetic disk device is controlled so as to read the sector number of the next sector without performing the processing for that sector. When after repetition of a series of the above-mentioned control the number of sectors of the objects to be processed which is the stored contents of the second register becomes zero (or if the stored contents of the second register is the sector number of the sector at which the processing is completed, when this sector number coincides with the sector number that is read out), the sector number that is read out signifies the sector number of the sector at which the processing is completed, so that the processing for this sector is performed, completing the processings for the track to which these sectors belong. Since in the prior art magnetic disk device as described in the above the processing will not be carried out until the stored contents of the first register, namely, the sector number of the processing starting point agrees with the sector number that is read out, the state in which there occurs no processing will persists until the sector number of the starting point of the processing which is the stored contents of the first register is read out even if the sector number read out first is the sector number of the sector of the object to be processed. For example, suppose that each track consists of 16 sectors which run from sector number (0) to sector number (15), the sector numbers of the objects to be processed are from (2) to (9), and the magnetic head is situated immediately in front of the sector number (6). Further, suppose that sector number (2) is stored in the first register. As the reading of the sector numbers starts the first sector number that will be read is (6) so that the coincidence with the sector number (2) stored in the first register will not be obtained. Accordingly, the processing for sector (6) will not take place, and the sector number (7) of the next sector will be read out. However, this sector number (7) neither coincides with the sector number (2) so that no processing will take place, and it will proceed to read the sector number of the following sector. In this manner, the state with no processing will persist for the sectors with sector numbers (8), (9), ..., (15), (0), and (1), and the processing will take place for the first time when the sector number (2) turns up. As in the above, in the prior art external memory control device, there will persist the state in which no processing for the sector of the current position of the head will take place even if the head is situated at a sector which is one of the objects to be processed, so that it will take longer time for completion of the processing of one track. The external memory devices for which control similar to the aforementioned magnetic disk control device applies include the flexible disk memory device and the optical disk memory device besides the magnetic disk device. U.S. patent 4,494,157 discloses an information read-out apparatus which reduces effective weight time and shortens access time, when information recorded on a magnetic disk is read out. When a sector on the magnetic disk on which a magnetic head is currently positioned is between a start address and an end address, information behind the current sector is buffered and the sequence of the buffered information is rearranged as required and read out so that overlapped read-out of the previously read information from the magnetic disk is prevented to shorten the access time. The current sector address is compared to the start address and the end address to process the information. U.S. patent 4,918,651 discloses a method and architecture for reading data from a track on a data disk with no latency in initiation of the data transfer due to sector alignment. Sector identification bytes are compared for track identification while sector number is written for storage in a table look-up with a buffer address for storage of the data. BRIEF SUMMARY OF THE INVENTION Summary of the Invention An external memory control device according to the present invention is disclosed in claim 1. Claims 2 to 8 disclose further embodiments of the present invention. An external memory control device includes a smallest sector number register and a largest sector number which store the smallest and the largest sector numbers, respectively, among the sector numbers belonging to one track designated by a processing request signal from the host system, a processing range detection part which detects whether the sector number read from the track belongs to the sector numbers within the processing range designated by the processing request signal based on the stored contents of these two registers, a sector processing discrimination part which generates a discrimination signal that is turned off when the sector number from the track is judged, based on the output of the processing range detection part and the contents of the two registers, to belong to the processing range and is the first sector number read from the track and is turned on when it is the second or a subsequent sector number to be read out, and is turned off when it is outside the processing range, and a processing completion control part which generates a processing completion signal when the sector signal read out is the sector number of the sector which is the last processing for the track. The external memory control device controls the external memory device so as to read the sector number of the next sector without carrying out the processing for the sector corresponding to the discrimination signal when the discrimination signal is turned off, to carry out the processing for the corresponding sector when the discrimination signal is turned on, then to proceed to read the next sector number, to carry out the processing for the sector corresponding to a processing completion signal in response to the generation of the processing completion signal, and to stop the reading of the sector number that follow. The sector processing discrimination part includes the selector number registers and a comparator, and when the sector number read from the track of the R/W designation of the processing request signal is a sector number within the processing rand and further is the number of sector read first from the track, the discrimination part stores the number of sector to be read next in the sector number register, and when the read sector number is the sector number read in the second or later time, updates the stored contents of the register to the sector number to be read next, moreover, when the sector number reaches the largest sector number, stores the smallest sector number in the register, finally when the sector number read from the track and the stored contents of the register are found to be coincident upon comparison in the comparator, generates a discrimination signal which is turned on. Moreover, the processing completion control part includes a processing residual register and a zero detection circuit, and the control part stores the total number of the sectors within the processing range before reading the sector number from the track of the R/W designation of the processing request signal, decrements the stored contents of the register by one whenever the discrimination signal is turned on, and the zero detection circuit generates the processing completion signal when the stored contents of the register becomes zero. Furthermore, the processing completion control part includes a processing completion sector number register, and when the sector number read out first from the track of the signal R/W designation is the sector number within the processing range, the control part stores the sector number as it is in the register, when it is a sector number outside the processing range, stores the largest sector number in the register, and when the sector number read out coincides with the stored contents of the register, generates a processing completion signal. As described in the above, in the external memory control device, when the sector number read out from the R/W designation track of the processing request signal is within the processing range designated by the signal, the processing will be started from the sector having the next sector number. Therefore, there is no need to hold the processing until the sector with the smallest sector number of the processing range, as was the case in the prior art control device, so that the time required for processing one track can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS The above-mentioned and other objects, features, and advantages of this invention will become more apparent by reference to the following detailed description of the invention taken in conjunction with the accompanying drawings, wherein: FIG. 1 is a block diagram for an example of a part of the magnetic disk control drive according to the prior art; FIG. 2 is a block diagram for another example of the same part as that shown in FIG. 1 of the magnetic disk control device according to the prior art; FIG. 3 is a plan view of the magnetic disk for describing the operation of the magnetic disk control device shown in FIG. 1 and FIG. 2; FIG. 4 is a block diagram for a first embodiment of the present invention; FIG. 5 is a plan view for the magnetic disk for describing the operation of the first embodiment; FIG. 6 is a block diagram for a second embodiment of the present invention; and FIG. 7 is a block diagram for a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1 which shows the block diagram for a portion of the prior art magnetic disk control device, this magnetic disk control device has a serial/ parallel converter 3, a sector processing discrimination part 5b, a processing completion control part 6, and a processing control part 7. The serial/parallel converter 3 is inserted between the magnetic disk control device shown in the figure and a magnetic disk device (not shown), and converts the sector numbers or the unit data that are transferred between them so as to be bit serial on the side of the magnetic disk device and to be bit parallel on the side of the magnetic disk control device. The sector processing discrimination part 5b includes a selector 52 which selects the smallest sector number ADmin among a series of sectors contained in a track designated by a processing request signal R/W from a host system during the period prior to the reading (in the reset state R) from the track and, after the elapse of the period for the reset state, selects and outputs the incremented sector number, a sector number register 54a which fetches the sector number from the selector 52 in response to a discrimination signal ACJ and outputs it, a comparator 55 which compares a sector number ADr which is an output read from the track supplied through the serial/parallel converter 3 and the sector number from the sector number register 54a and generates a discrimination signal ACJ which is turned on when both numbers coincide, and an adder 56 which outputs a sector number obtained by incrementing the sector number output by the sector number register 54a by one unit of the reading interval (for example, it is "1" if the adjacent sectors are sequentially read in continuous fashion, and it is "2" if every other sector is read). As described in the above, in this sector processing discrimination part 5b, the smallest sector number among a large number of sector numbers that belong to a track is stored in the sector number register 54a prior to the reading of the first sector number of the track, and the discrimination signal ACJ is turned on when the smallest sector number coincides with the sector number ADr, by which the contents of the sector number register 54a is updated. In other words, the sector processing discrimination part 5b outputs a discrimination signal ACJ by turning it on when the sector number read becomes equal to the smallest sector number ADmin and updates the stored contents of the sector number register 54a to the next sector number, and thereafter, the turning on of the discrimination signal ACJ and the updating of the stored contents of the register 54a are repeated whenever the sector number read out coincides with the sector number from the register 54a, and the discrimination signal ACJ is kept in the off-state and the stored contents of the register 54a are also left as they are. The processing completion control part 6 has a substrator 61 which computes and outputs the sector number within the processing range of a track from the smallest sector number ADmin and the largest sector number ADmax designated by the processing request signal R/W from the host system, a selector 62 which selects the sector number from the subtractor 61 in the reset state (R) and selects the decremented sector number otherwise, a processing residual register 63 which fetches to store and outputs the sector number from the selector 62 whenever the reset state and the discrimination signal ACJ are in the on-state, a subtractor 64 which outputs the sector number from the register 63 decremented by "1", and a zero detection circuit 65 which generates a processing completion signal END by detecting that the sector number from the register 63 is zero. As in the above, the processing completion control part 6 stores the sector number within the processing range of the processing request signal R/W in the processing residual register 63, decrements the sector number every time when the discrimination signal ACJ is in the on-state, generates a processing completion signal END when the sector number goes to zero, and detects by this that the processing for one track is completed. The processing control part 7 receives the processing request signal R/W, the discrimination signal ACJ and the processing completion signal END, and when the discrimination signal ACJ corresponding to the sector number read from the track is in the off-state, it proceeds to read the sector number of the next sector without performing the processing for the sector with that sector number, and performs the processing for the sector with that sector number and reads the sector number of the next sector when the discrimination signal ACJ is in the on-state. This operation is repeated thereafter, and subsequent to the execution of the processing for the sector with the sector number corresponding to a processing completion signal END in response to the generation of a processing completion signal END, the reading of sector numbers for the ensuing sectors is stopped. This completes the processing for one track. As in the above, the magnetic disk device controlled by this magnetic disk control device starts to carry out the processing for the sector with a sector number read from the track of R/W designation of the processing request signal when the sector number read coincides with the smallest sector number within the processing range designated by R/W of the same signal, and thereafter carries out sequentially the processing for each sector and when the sector number reaches the largest value within the processing range, the processing for that sector is completed. This completion indicates none other than the completion of the processing for one track. Next, referring to FIG. 2 which shows another example of the magnetic disk controls device of the prior art, this example is identical to the example shown in FIG. 1 except for a part of a processing completion control part 6b, so that the components common to FIG. 1 are assigned common reference numerals to omit further detailed explanation. The processing completion control part 6b has a processing completion sector address register 68 which stores the largest sector number ADmax within the processing range of the track of the processing request signal R/W designation during the reset state (R) period and outputs it later, and a comparator 69 which generates a processing completion signal END in response to the coincidence of the largest sector number from the register 68 and the sector number of the read output supplied by the serial/parallel converter 3. Except for the above-mentioned point the structure of the present example is the same as that of the sample shown in FIG. 1. Referring to FIG. 3 which actually shows the operation of the processing for the sectors on a magnetic disk by means of the prior art magnetic disk control devices shown in FIG. 1 and FIG. 2, magnetic disk 100 contains a plurality of tracks 101 where these tracks are each subdivided into 16 sectors having sector numbers from (0) to (15). Assume that a magnetic head selected according to the R/W designation of a processing request signal from the host system is moved to a predetermined track 101, and is located in the initial state before the read of the sector number at a position immediately in front of the sector number 6 (position of SHP in FIG. 3). Further, assume that the sectors of the object for processing are from sector number (2) to sector number (9) (namely, the "processing range" is from sector (2) sector (9)), and that the processing for these sectors is carried out sequentially. As may be clear from the above description, the sector number (2) is stored under these conditions in the sector number register 54a. With the start of read of the sector numbers of the track 101, the sector number to be read first is (6) so that the result of comparison by the comparator 55 is noncoincidence, and the discrimination signal ACJ remains in the off-state. As a result, the processing for the sector with sector number (6) is not carried out, and the sector number (7) is read out. Since neither the sector number (7) coincide with the stored contents of the sector number register 54a, that is, the sector number (2) so that the discrimination signal ACJ remains in the off-state, and the processing for the number (7) is nor carried out and the sector number (8) of the next sector is read out. As in the above, the state with no processing persists up to the sectors with sector number (1), namely, for the sectors from sector number (6) to sector number (1). When sector number (2) is read, it coincides with the sector number (2) that is stored in the selector number register 54a so that the processing for the sector with number (2) is carried out. At the same time, the stored contents of the register 54a, namely, the sector number (2) is updated to (3). On the other hand, the sector number (3) of the next sector is read and these sector numbers are compared in the comparator 55. In this way, the processing for sectors up to the sector number (8) is completed and the sector number (9) is stored in the register 54a. On the other hand, when the sector number (9) is read, the processing completion control part 6 or 6b generates a processing completion signal END, the processing for the track 101 is completed with the completion of the processing for the sector with the section number (9). As in the above, in the magnetic disk control device according to the prior art, despite the fact that the magnetic head is situated at a sector position within the processing range of the processing request signal R/W designation, the state with no processing for these sectors and as a result, the time required for processing one track is increased. Next, referring to FIG. 4 which shows the principal part of the first embodiment of the present invention, the magnetic disk control device according to the present embodiment is constituted of a smallest sector number register 1 which stores the smallest sector number corresponding to the sector of the starting point of processing for one track designated by the processing request signal R/W from the CPU, a largest sector number register 2 which stores the largest sector number corresponding to the sector of the completion point of the same processing as in the above, a serial/parallel converter 3, a processing range detection part 4, a sector processing discrimination part 5, a processing completion control part 6 and a processing control part 7. As is clear from the constitution shown in the figure, the present embodiment differs from the prior art magnetic disk control device shown in FIG. 1 in that there are added the smallest sector number register 1, the largest sector number register 2 and the processing range detection part 4, and in the internal constitution of the sector processing discrimination part 5. The smallest sector number register 1 and the largest sector number register 2 stores the smallest sector number and the largest sector number, respectively, among a large number of sectors within the processing range of one track. The processing range detection part 4 compares the sector number ADr read from the track of the R/W designation of the signal supplied by the serial/parallel converter 3 with the smallest and the largest sector numbers from the smallest sector number register 1 and the largest sector number, respectively, and identify whether the sector number ADr is a sector number within the processing range. Such a processing range detection part 4 can easily be realized by the combination of a comparator which compares the magnitude of the sector numbers and a logic gate. The sector processing discrimination part 5 includes an adder 51 which adds one unit (ordinarily one) of the sector reading interval to the sector number ADr that is read out, a sector number register 54 which fetches to store the supplied sector number at the time of reading the first sector number of a track (timing pulse 1R) and at other times fetches to store and outputs the sector number in response to the on-state of the discrimination signal ACJ, a second adder 56 which outputs a sector number obtained by incrementing the sector number from the sector number register 54 by one unit of the sector read interval, a first selector 52 which selects the sector number from the first adder 51 at the time of reading of the first sector number (1R) of the track and at other times selects and outputs the incremented sector number from the second adder 56, a comparator 58 which compares the largest sector number from the largest sector number register 2 and the sector number from the sector number register 54 and detects whether these sector numbers coincides with each other, a flip-flop 57 which goes to the reset state when the result of comparison of the initial state and the comparator 58 coincides and goes to the set state when it is judged by the detection part 4 that the sector number ADr that is read is within the processing range, a second selector 53 which selects the sector number from the selector 52 when the flip-flop 57 is in the set state and selects the sector number from the smallest sector number register 1 when the flip-flop is in the reset state and supplies it to the sector number register 54, and a comparator 55 which compares the sector number ADr that is read and the sector number from the sector number register 54 and generates a discrimination signal ACJ which goes to the on-state when they coincide and goes to the off-state when they do not coincide. The serial/parallel converter 3, the processing completion control part 6, and the process control part 7 are identical to those of the prior art shown in FIG. 1 so that the description about them will be omitted. Next, referring to FIG. 5 showing a plan view analogous to FIG. 3, a trace 101 of a magnetic disk 100 are segmented into 16 sectors with sector numbers from (0) to (15), and it will be assumed that the sectors (2) through (9) are designated as a processing object. In order to describe first the case where the sector number ADr read out first from the track 100 is within the processing range designated by R/W of a processing request signal it will be assumed that the magnetic head position SHP in the initial state is located at a position immediately in front of the sector with sector number (6). When it is detected that the sector number ADr read out first from the W/R designation track is located within the processing range, the flip-flop 57 goes to the set state and the selector 53 selects the output of the selector 52, the selector 52 selects the output of the adder 51, and the sector number register 54 updates its storage contents. Accordingly, the sector number (7) following the sector number read first ((6) in FIG. 5 which manner will be analogous hereinafter) is stored in the sector number register 54. For the sector number (6) which was read first, the sector number register 54 changes from the state where nothing is stored to the state where the sector number (7) is stored, the result of comparison in the comparator 55 is "noncoincidence" so that the discrimination signal ACJ remains the off-state. Since no processing is given for the sector with the sector number (6), the next sector number (7) will be read out. Since the sector number (7) that is read out next coincides with the stored contents of the sector number register 54, the discrimination signal ACJ is turned on, the processing for the sector with the sector number (7) is carried out by the processing control part 7, and the next sector number (8) is read out. At the same time, the stored contents of the sector number register 54 is updated by the discrimination signal ACJ to the sector number (8). When the stored contents of the sector number register 54 is updated to sector number (9) which is the largest sector number within the processing range after repetition of the operation analogous to what is described in the above, the flip-flop 57 is brought to the reset state by the comparator 58, and the selector 53 selects the output of the smallest sector number register 1, that is, the smallest sector number within the processing range. As the sector number (9) is read out and the discrimination signal ACJ is turned on, the storage contents of the sector number register 54 is updated to the smallest sector number (2). After the processing for the sector with the sector number (9), the sector number that is read out is (10) so that the discrimination signal ACJ is turned off, and the reading for the next sector number is carried out without processing for the sector with the sector number (10). At this time, the stored contents of the sector number register 54 is not updated. Thereafter, similar operation is repeated, and reading of the sector number alone is carried out until the sector number (1) is arrived at. When the sector number (2) is read, the discrimination signal is turned on, and the sector number (3) is read out after giving the processing for the sector with the sector number (2). At the same time, the flip-flop 57 is brought to the set state by the processing range detection part 4, and the stored contents of the sector number register 54 is updated to (3) via the adder 56, the selectors 52 and 53. Thereafter, similar operation will be repeated. On the other hand, the sector number which is the storage contents of the processing residual register 63 is reduced every time when the discrimination signal ACJ is turned on, and when the discrimination signal ACJ is turned on upon reading of the sector number (6), the sector number which is the storage contents of the processing residual register 63 becomes zero. The zero detection circuit 65 which responds to this situation outputs a processing completion signal END, and after carrying out the processing for the sector with the sector number (6) the processing control part 7 ceases reading the sector number chat follow. With the above-mentioned operation all the processing for the sectors within the processing range of the track designated by R/W of the processing request signal is ended, completing the processing for the track. If the first read sector number ADr is outside the range of processing ((14), for example), the flip-flop 57 is brought to the reset state by the processing range detection part 4, the output of the smallest sector number register, namely, the smallest sector number (2) is selected by the selector 53, and the result is stored in the sector number register 54. Thereafter, reading of the sector number alone takes place until the sector number (2) is read out. The operation following the read of the sector number (2) is the same as the aforementioned operation for the sectors within the processing range. When the largest sector number (9) is reached, there is generated a processing completion signal END is issued, and the processing for one track is completed with the ending of the processing for the sector with the sector number (9). As described in the above, in the present embodiment, if the sector number read first from a track designated by R/W of a processing request signal falls within the processing range of R/W designation of the request signal, the processing is started from the sector following the read sector, so that it is possible to shorten the time requried for processing the sectors in the track. It should be mentioned that the reason for arranging to start the processing from the sector following the sector read out first is that, at the time of transmission of the sector number read out to the comparator 55, there is not yet stored the desired sector number in the sector number register 54. Next, referring to FIG. 6 showing the second embodiment of the present invention, the sector processing discrimination part 5a combines the two adders 51 and 56 in the first embodiment into a single adder 51, the sector number first read from the track designated by the signal R/W or the output of the sector number register 54 is supplied to the adder 51 according to the selection by the selector 52, and supplies the output of the adder 51 to the selective input on the set (S) side of the selector 53. Other parts of the operation are the same as in the first embodiment. Namely, the second embodiment is the same as the first embodiment except for the fact that the function of the adder 56 is let to be served by the adder 51 so that further description will be omitted. The second embodiment is more advantageous than the first embodiment in that its circuit constitution can be simplified. Referring to FIG. 7 which shows the third embodiment of the present invention, this third embodiment is the same as the first embodiment except for the constitution of a processing completion control part 6a, so that the description that follows is limited to that of the control part 6a, omitting the description about the remaining parts. The processing completion control part 6a includes a processing completion sector number register 68 which fetches to store and outputs the sector number ADr read out first from the track designated by the R/W signal, an AND type logic circuit 66 which outputs a signal which is turned on when the detection part 4 recognizes that the sector number read out first falls within the processing range designated by a R/W signal, a selector 67 which selects the sector number that was read out first when the output signal of the logic circuit 66 is in the on-state and selects the largest sector number from the largest sector number register 2 and sends the selected result to the processing completion sector number register 68, and a comparator 69 which issues a processing completion signal END when the sector number ADr and the sector number from the processing completion sector number register 68 are coincident with each other. In the third embodiment, if the sector number read out first from the track designated by the R/W signal falls within the processing range designated by the R/W signal, the sector number is stored at the timing of reading the first sector number in the processing completion sector number register 68. For the sector with the first read sector number, no processing is carried out (analogous to the first and the second embodiments). Thereafter, the operation similar to that of the first embodiment is repeated, and when the sector number read out first is read again, a processing completion signal END is output from the comparator 69 to give the processing for the sector with that sector number, by which the processing for one track is completed. When the sector number that is read first falls outside of the processing range, the largest sector number within the processing range is stored in the processing completion sector number register 68. Since the operation thereafter is similar to the example of the prior art magnetic disk control cevice shown in FIG. 2 so that a further description will be omitted. The third embodiment is more advantageous than the first embodiment in that it is possible to simplify the processing completion control part. Further, in the third embodiment, it is possible to replace the sector processing discrimination part 5 with the sector processing discrimination part 5a (FIG. 6) of the second embodiment. The aforementioned three embodiments are given in the form of a magnetic disk control device which controls the magnetic disk, but the external memory control device according to the present invention is also applicable to the external memory devices using different storage medium so long as the data constitution is common, such as a flexible disk device and an optical disk device.

Claims: An external memory control device which controls an external memory device so as to carry out processings such as read or write of data for every unit amount of said data for storage areas designated by processing request signals in said external memory device in response to said processing request signals from a central processing unit, whereby said external memory device is a memory device which has a large number of concentric storage tracks each being subdivided into a plurality of unit storage areas that can store unit amounts of said data on the surface of a circular platelike storage medium, and said designation of said storage area is carried out by means of specification of said storage track and said unit storage areas that correspond to the starting point and the completion point of said processing to the track, the external memory control device comprising: a first (1) and a second (2) registers which respectively store the smallest identification number and the largest identification number among the identification numbers of said unit storage areas belonging to a designated track that are designated by said processing request signal; processing range discriminating means (4) which discriminates whether the identification number read out from said designated track is a unit storage area contained in the processing range designated by said processing request signal; said external memory control device being characterized in that it further comprises: unit storage area discriminating means (5) which generates in response to the processing range discriminating means a discrimination signal (ACJ) which is turned off when said identification number read from said designated track is an identification number of a unit storage area contained in said processing range and is the identification number read first from the designated track, turned on when said identification number is an identification number of a unit storage area contained in said processing range and is an identification number read out by second or subsequent reading from the designated track, and turned off when said identification number is an identification number of a unit storage area which is not contained in said processing range; processing completion control means (6) which generates a processing completion signal (END) when said identification number read out from said designated track in response to the unit storage area discriminating means (5) is an identification number of a unit storage area which is the object of the last processing among the unit storage areas within said processing range; and terminating means (7) which starts the reading of the identification number of the unit storage areas that belong to said designated track in response to said processing request signal, reads the identification number of the following unit storage area without carrying out the processing for the unit storage area corresponding to the discrimination signal (ACJ) when said discrimination signal (ACJ) is in the off-state, reads out the identification number of the following unit storage area after carrying out the processing for the unit storage area corresponding to the discrimination signal (ACJ) and carries out the processing for the unit storage area of the processing completion signal in response to said processing completion signal, then terminates the read of the subsequent identification numbers. An external memory control device as claimed in claim 1, wherein said external memory device is a magnetic disk device. An external memory control device as claimed in claim 1, wherein said unit storage discriminating means (5) comprises an identification number register (54) which stores the identification number that is read next, when said identification number read from said designated track is an identification number of a unit storage area which is contained in said processing range and is the first identification number read from the track; means for updating the identification number which is the stored contents of said identification number register (54) to the identification number of the unit storage area following the identification number at a predetermined timing, when the identification number read from said designated track is an identification number of a unit storage area within said processing range and is an identification number read out in a second or later reading from the track; means for storing at a predetermined timing the smallest identification number of the identification numbers in the identification number register, when the identification number which is the stored contents of said identification number register (54) is the largest identification number among the identification numbers of the unit storage areas contained in said processing range; and a comparator (55) which generates said discrimination signal (ACJ) which is turned on when said identification number read from said designated track and the identification number which is the stored contents of the said identification number register (54) are found to be coincident upon comparison. An external memory control device as claimed in claim 3, wherein said smallest identification number is arranged to be stored in said identification number register (54) in the initial state prior to the reading of said identification number from said designated track. An external memory control device as claimed in claim 1, wherein said processing completion means (6) comprises a processing residual register (63) which stores the total number of the unit storage areas contained in said processing range in the initial state prior to the reading of said identification number from said designated track, means (64) for decrementing said total number by count one every time when said discrimination signal is turned on, and zero detection means (65) which generates said processing completion signal when said total number which is the stored contents of said processing residual register (63) becomes zero. An external memory control device as claimed in claim 1, wherein said processing completion control means (65) comprises a processing completion identification number register (68) which stores the identification number when the identification number read from said designated track is an identification number of a unit storage area that is contained within said processing range and stores the largest identification number among the identification numbers of the unit storage areas contained within said processing range when the identification number is outside of the processing range, and means (69) which generates said processing completion signal when the identification number read from said designated track and the identification number which is the stored contents of the register (68) are found coincident with each other upon comparison. An external memory control device as claimed in claim 3, said unit storage area discriminating part (5) comprises: a first adder (51) which adds count one to the identification number read from said designated track; an identification number register (54) which stores and outputs said identification number read from said designated track at predetermined timings; a second adder (56) which adds count one to the identification number which is the stored contents of the identification number register; a first comparator (58) which compares the identification number which is the stored contents of said largest identification number register (2) and the identification number which is the stored contents of said identification number register (54); a flip-flop (57) which goes to the reset state in said initial state or when the output of said first comparator (58) shows the noncoincidence of the two identification numbers that are its objects of comparison and goes to the set state when the output of said processing range discriminating means (4) shows that it is an identification number within said processing range; a first selector (52) which selects the identification number from said first adder (51) only when said identification number is the identification number read first from said designated track and selects the identification number from said second adder (56) in other times and outputs the selected result; a second selector (53) which selects the identification number which is the stored contents of said smallest identification register (1) when said flip-flop (57) is in said reset state and selects the identification number from said first selector (52) when said flip-flop (57) is in said set state and supplies the selected result to said identification number register (54); and a second comparator (55) which outputs said discrimination signal (ACJ) which is turned on when the identification number read from said designated track and the identification number which is the stored contents of said identification register (54) are found coincident upon comparison. An external memory control device as claimed in claim 7 further comprising a unit storage area discriminating part (5a) wherein said first and said second adders are combined into one adder (51), said first selector (52) is constituted of circuit means which selects the identification number of said unit storage area only when said identification number is the identification number read first from said designated track and selects the identification number which is the stored contents of said identification number register (54) in other times and outputs the result to the adder (51), and supplies the output of said first adder (51) to the input end on the selected side when said flip-flop (57) of said second selector (53) is in the set state.

Inventors: ISHIKAWA YUTAKA, SATO NOBORU, ISHIKAWA, YUTAKA, SATO, NOBORU, Ishikawa, Yutaka, c/o NEC Corporation, Sato, Noboru, c/o NEC Corporation
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1991
Main classification: G06F3
IPC codes: G11B19, G06F3