Data transfer system

Abstract: A data transfer system includes a buffer (28) having a plurality of buffer areas for storing the data blocks transferred from plural central processors (10,12,14,16), and an external pointer (32) storing an address data corresponding to an initial position of one of the buffer areas where a transferring data block is to be stored therein. The address data stored in the external pointer (32) is updated in accordance with the length (Lb) of a data block to be transferred. The length data (Lb) is supplied with the address to the external pointer (32) where the length data (Lb) is added (50) to the buffer area address (PTRe) output by a RAM (46) and the sum (X) is stored as the next buffer area address (PTRe) in the RAM (46).

Description: FIELD OF THE INVENTION This invention relates to a data transfer system, and more particularly to, a data transfer system using an auto-increment-pointer. BACKGROUND OF THE INVENTION A conventional data transfer system, using an auto-increment-pointer, includes a plurality of central processors, an I/O panel having a buffer, an internal pointer and an external pointer, and a system bus connecting between the central processors and the I/O panel. The buffer includes a predetermined number of buffer areas accessed by the central processors and the I/O panel. The external pointer stores an initial address for access to the buffer areas by the central processors and the internal pointer stores an initial address for access to the buffer areas only by the I/O panel. The priority is decided among the central processors by a bus arbitration circuit. In the conventional data transfer system, when the external pointer is read by one of the central processors which is selected by the bus arbitration circuit, an address data stored in the external pointer is supplied to the central processor. Then, a predetermined data block is transferred from the central processor to the buffer area in write mode designated the address data of the external pointer. At this time, in the external pointer, an address value "1" is automatically added to the precedent address data, and the added address is stored in the external pointer as a subsequent address. In the same manner, read mode is carried out between the central processors and the I/O panel. On the other hand, when the internal pointer is accessed by the I/O panel, a predetermined data block is transferred from the buffer, for instance, to a periphery circuit in accordance with an address data stored in the internal pointer. According to the conventional data transfer system, however, there are disadvantages in that when a transferred data block has a length longer than that of the buffer areas, the data block has to be divided so that the divided data is shorter than the length of the buffer areas, because the length of the buffer areas is fixed to be a predetermined length. As a result, a transfer speed is low. On the other hand, if a length of a transferred data block is shorter than that of the buffer area, a portion of the area is useless in the buffer. In US 4,599,689, a control apparatus for direct memory access (DMA) transfers is shown. This has a memory divided into a plurality of buffers. Each buffer has an overrun section assigned to it which is an additional memory area appended to the buffer. Prior to transfer, the buffers containing data to be transferred are threaded to form a single area by copying data of the second data block of the buffer into the overrun section of the preceding data block buffer. Data transfer is not stopped but interrupted when a specified buffer is read out but continues with transferring the overrun section. The system corrects address and word count information from DMA so that the last data from overrun and the first word of the next data block buffer are contiguous. SUMMARY OF THE INVENTION Accordingly, it is an object of the invention to provide a data transfer system which operates with high speed. It is another object of the invention to provide a data transfer system in which a buffer can be used efficiently. It is a further object of the invention to provide a data transfer system in which a data block stored in the buffer can be read from its initial point at any time. The invention is concerned with a data transfer system, including: at least two processors each having a predetermined data block to be transferred; a buffer having a predetermined number of buffer areas for storing data blocks transferred from the at least two processors; and an external pointer storing an address data designating to an initial position of one of the buffer areas; wherein the address data is increased or decreased by a value determined in accordance with a ratio between a length of the data block and a length of the buffer areas. The invention is defined in apparatus claim 1. Further embodiments are specified in the appended dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be explained in more detail in conjunction with appended drawings; wherein: Fig. 1 is a block diagram showing a data transfer system of a preferred embodiment according to the invention; Fig. 2 is a format of a data transferred from a central processor to an I/O panel in the preferred embodiment; Fig. 3 is a format of a data block transferred from a central processor to a buffer in the preferred embodiment; Fig. 4 is an explanatory view showing operation of the I/O panel (an external pointer) of the preferred embodiment; Fig. 5 is a memory map of a two-port RAM used in the preferred embodiment; Fig. 6 is a block diagram showing an external pointer used in the preferred embodiment; Figs. 7 and 8 are flow charts showing operation of the preferred embodiment; and Fig. 9 is a format of a data stored in the buffer. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 1 shows a data transfer system of a preferred embodiment according to the invention. The data transfer system includes four central processors 10, 12, 14 and 16, an I/O panel 18 connected to a line 20, a system bus 22 connecting between each of the central processors 10, 12, 14 and 16 and the I/O panel 18, and a bus arbitration circuit 24 connected to the central processors 10, 12, 14 and 16, respectively. The bus arbitration circuit 24 controls the central processors 10, 12, 14 and 16 to access to the I/O panel 26 without a confliction among them. The I/O panel 18 includes a two-port RAM 26 having a buffer 28, and internal and external pointers 30 and 32 storing address data PTRe and PTRi for access to the buffer 28 by the central processors 10, 12, 14 and 16 and the I/O panel 18, respectively. Each of the central processors 10, 12, 14 and 16 supplies an increment data "Lb" corresponding to a length of a transferred data block to the external pointer 32 in addition to the address data PTRe, so that a data 100 is obtained as shown in Fig. 2. At the same time, each of the central processors 10, 12, 14 and 16 transfers a data block including a buffer busy flag "B", a header "HEADER" and a length data "Li" of the transferring data block to the buffer 28 as shown in Fig. 3. The header "HEADER" is determined to be a different value relative to the other data blocks to avoid a confusion among them. The address data PTRe is renewed in the addition of the increment data "Lb" thereto as shown in Fig. 4. Fig. 5 shows a memory map of the two-port RAM 26 having two aspects between for the I/O panel 18 and for the system bus 22. That is, for the I/O panel 18, the two-port RAM 26 has addresses $0000 to $7FFF to be composed of a RAM area having addresses $8000 to $FFFF. On the other hand, for the system bus 22, the two-port RAM 26 is composed of a buffer area 28E, an external pointer area 32E and an internal pointer area 30E corresponding to the buffer 28, the external pointer 32 and the internal pointer 30, respectively, as shown in Fig. 1. The buffer area 28E is accessed in read and write modes by the central processors 10, 12, 14 and 16. The external pointer area 32E stores an address data for access to the buffer area 28E, and is accessed in read and write modes by the central processors 10, 12, 14 and 16. When the presently stored address is read by the central processor 10, 12, 14 or 16, the address data is renewed automatically in accordance with the increment data "Lb" for the subsequent access to the buffer area 28E. The internal pointer area 30E cannot be accessed by the central processor 10, 12, 14 and 16, while it is accessed only by the I/O panel 18. Fig. 6 shows the external pointer 32 including a timing controller 40 supplying timing signals RWS, RDGATE, LATCH, INGATE and WSEL, a decoder 42 for decoding an address signal, a gate 44 for controlling the transfer of a data, a RAM 46 for storing a predetermined data, a latch circuit 48 connected between the gate 44 and the RAM 46 for latching a signal read from the RAM 46, an adder 50 for adding the read address data A and an increment data B, a selector 52 for selecting an input signal between X and Y to write an output signal Q to the RAM 46, and an address controller 54 for masking the increment data "Lb" of the data 100. The I/O panel 18 including the external pointer 32 operates in first and second modes. The first mode is carried out as an ordinary operation, when an address signal is decoded in the decoder 42 for access to addresses other than an address assigned to the external pointer 32, and the second mode is carried out-as a specified operation to embody the invention, when an address signal is decoded therein for access to the address signal assigned to the external pointer 32. (a) FIRST MODE In writing mode, the gate 44 is closed and the input Y of the selector 52 is opened, so that a predetermined data is supplied to the RAM 46 through the selector 52. In reading mode, a data stored in the RAM 46 is supplied to the system bus 22 through the latch circuit 48 and the gate 44. (b) SECOND MODE Here, it is assumed that the central processor 10 is selected to access to the exterior pointer 32 by the bus arbitration circuit 24. An address signal designating the RAM 46 assigned to the external pointer 32 is supplied to an address bus to be connected to the decoder 42. An AINC (auto-increment) signal is generated in the decoder 42 to be supplied to the controller 40 by decoding the address signal excluding lower eight bits assigned to an auto-increment data, so that the gate 44 and the latch circuit 48 become to be opened. Thus, an address data stored in the RAM 46 is supplied to the central processor 10 through the latch circuit 48 and the gate 44. The increment data "Lb" is supplied to the address bus together with the read address signal. At the same time, the read address data is latched at the latch circuit 48 to be supplied to the input A of the adder 50, so that the address data is added with the increment data "Lb" supplied from the address bus to the input B of the adder 50. The added data is supplied through the selector 52 to the RAM 46, so that the added data is stored therein as a renewal address data. Finally, a signal DTACK indicating a finish of the access is supplied from the controller 40 to the central processors 10. The central processor 10 transfers the data to be written to the buffer 28 by accessing to the address supplied from the external pointer 32. Next, this described operation will be again explained in conjunction with Figs. 7 to 9. In Fig. 7, it is also supposed that the central processor 10 is selected by the bus arbitration circuit 24. When the selected signal is supplied from the bus arbitration circuit 24 to the central processor 10, the central processor 10 supplies a predetermined signal to the external pointer 32. In response to the signal supplied from the central processor 10, an address data PTRe stored in the external pointer 32 is supplied to the central processor 10. At the same time, the central processor 10 detects a block length "Li" of a transferred data block (S31), and an auto-increment data "Lb" is calculated in accordance with the block length "Li" (S32) to produce an address signal 100 including the increment data "Lb" as shown in Fig. 2. For example, if it is supposed that the minimum storing bit length of the external pointer 32 is sixty four bits, the block length "Li" is divided by sixty four. Then, an integer value of the divisional calculation result is added to the value "1" to provide the increment data. Next, the renewal data 100 is supplied from the central processor 10 to the external pointer 32 through the system bus 22 (S33). The increment data "Lb" is added to the read and latched address data, so that a subsequent address data representing an initial address of a subsequent data transferred from another central processor is stored therein instead of the precedent address data. After that, an intial address of the data block is determined in accordance with the data of the external pointer 32 (S34), so that the data block is transferred from the central processor to the buffer 28 (S35). When the data transfer is finished, the buffer busy flag "B" becomes "1" (S36). Fig. 8 shows a flow chart of the preferred embodiment in a case that a predetermined data stored in the buffer 28 is supplied to the line 20 by using the internal pointer 30. When an initial address of a transferred data block is designated accordance with an address data PTRi stored in the internal pointer 30 (S41), a header "HEADER" is judged to be set or not at a position having a predetermined relation to the detected initial address (S42). When the header "HEADER" is detected as shown in Fig. 9 at "a" and "b", the buffer busy flag "B" is judged to be set to be "1" or not (S43). When the buffer busy flag "B" is set to be "1", the data block is read from the initial address and is transferred to the line 20 (S44). If the buffer busy flag "B" is not set to be "1", the data block is not read until the busy flag becomes "1". When the transfer is finished, the buffer busy flag "B" is reset to be "0" (S45), the precedent address data PTRi of the internal pointer 30 is renewed in accordance with the block length "Li", and back to the step S41. If the address data PTRi stored in the internal pointer 30 designates a midpoint of the data block, at which a header "HEADER" is not detected as shown in Fig. 9 at "c", a header "HEADER" is searched in the buffer 28 (S47), the wrong address data is amended in accordance with a position of the searched header "HEADER" (S48), and back to the step S41. As described above, according to the preferred embodiment, the address data PTRe of the external pointer 32 is renewed in accordance with a length of a transferring data block, so that the data block can be transferred at one time. Therefore, operating speed of the system becomes high. Further, there is decreased useless area in each of the buffer areas, so that the buffer 28 can be used efficiently. In addition, the transferring data block includes a header "HEADER", so that a data block stored in the buffer can be read from its initial point at any time.

Claims: A data transfer system, comprising: at least two processors (10,12,14,16) each having a predetermined data block to be transferred; a buffer memory (28) having a predetermined number of buffer memory areas for storing data blocks transferred from said at least two processors; and a pointer (32) accessed by a selected one of said at least two processors (10, 12, 14, 16) and, storing address data designating an initial address in said buffer memory; characterised by means for increasing or decreasing said address data (100) by a value determined in accordance with the ratio between the length of said data block and the length of a storing area of said buffer memory. A data transfer system according to claim 1 characterised in that said pointer (32) and said buffer memory (28) are included in an Input/Output panel (18). A data transfer system according to claim 1 further characterised by: a further pointer (30) in said Input/Output panel (18) storing address data designating an initial address in said buffer memory storing said data block transferred from said processors, said data block being read from said initial address of said buffer memory to be transferred to a periphery circuit, wherein said data block has a header representing said initial address of said data block; and said header is searched when said data block stored in said buffer is read; and said stored data block is read from said header in accordance with said address data stored in said pointer. A data transfer system according to claim 3 characterised in that: said address data is corrected to be an address data representing a position of said searched header, if said header is not set at a predetermined position. A data transfer system according to any preceding claim characterised by: a system bus (22) for transferring data from said plurality of central processors to said buffer memory; and a bus arbitration circuit (24) for arbitrating a use of said system bus by a central processor selected from said plurality of central processors. A data transfer system according to claim 1 characterised in that: said pointer (32) is included in an I/O panel (18), said I/O panel including a further pointer (30) for storing an address signal designating an initial address of said buffer memory, a data block being read from said initial address of said buffer memory to be transferred to a periphery circuit. A data transfer system according to claim 6 characterised in that: said pointer (32) is accessed by said plurality of central processors, while said further pointer (30) is accessed by said I/O panel (18).

Inventors: SUZUKI HIDETO, SUZUKI, HIDETO
Applicants: NIPPON ELECTRIC CO, NEC CORPORATION
Application year: 1992
Main classification: G06F13
IPC codes: G06F13, G06F15, G06F5