JP3455379B2 - Speed conversion circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ATM (Asynchronous
The present invention relates to a speed conversion circuit used for various devices of an ous Transfer Mode (asynchronous transfer mode) system, and particularly to a wideband ISDN.
LSI that realizes AAL (ATM Adaptation Layer) part on (Integrated Serviced Digital Network) protocol
The present invention relates to a speed conversion circuit for accommodating different line speeds of SAR (Segmentation And Reassembly). 2. Description of the Related Art FIG. 7 shows a conventional configuration of an SAR unit. In the SAR processing unit, the processing described below is performed. First, on the receiving side, the data width of the cell (see FIG. 3) received from the line is converted from 8 bits to 32 bits by the 8-bit / 32-bit conversion unit 51, and the reception FIFO (First-In Firs) is used.
(t-Out) unit 52 replaces the clock with the internal operation clock, temporarily stores it in the receiving buffer unit 53, and then uses the message assembling control unit 54 to assemble the message in the external memory unit 61 based on the information in the header of the cell. Is retrieved, the payload of the cell is stored in the external memory 61 via the INF (interface) unit 55 based on the information, and the message is assembled by connecting them (see FIG. 4). On the transmitting side, a message to be sent is stored in the external memory unit 61 from the upper CPU unit 62, and when it is transmitted, header information of the cell is set from the upper CPU unit 62 and transmitted to the cell division control unit 56. The message is divided into cells by reading the message from the external memory unit 61 in units of 48 bytes, and a cell with a header added at the beginning is temporarily stored in the transmission-side buffer unit 57, and then transmitted.
In part 58, the clock is replaced with the line clock.
The data is converted into an 8-bit data width by an 8-bit conversion unit 59 and transmitted. As described above, in the receiving process, the control information of the channel and the information for assembling the message are read out from the external memory unit 61 based on the VPI / VCI (channel number) in the header of the cell, and then the external memory unit 6
The payload section is transferred from the receiving buffer section 53 to the external memory section 61 on the basis of the information read from No. 1. In the transmission process, the header information of the channel to be transmitted is received from the upper CPU 62, the message is read from the external memory 61, and the header is added to the message and stored in the transmission buffer 57. FIGS. 8 and 9 show time charts of the transmitting side (1) and the receiving side (2), respectively. In the time charts of FIG. 8 and FIG.
It corresponds to the cell flow in the middle. Here, since the receiving process and the transmitting process are asynchronous, if the memory access timing of the message assembling process and the cell dividing process is simultaneous, as shown in (1) of FIG. Becomes longer (1280 ns), and when the memory access of the message assembling process and the cell dividing process does not overlap and only one of the processes is performed, the processing time is shortened as shown in (2) of FIG. (720n
s). However, according to the above-described prior art, the transmission / reception FIFO units 52 and 58 convert the speed of the line side clock and the internal operation clock, and then convert the transmission / reception side. Since the data is temporarily stored in the buffer units 53 and 57 and the timing of the internal processing is adjusted by the transmitting and receiving buffer units 53 and 57, four memories for storing cells are required in total on the transmitting and receiving sides. There is a problem that the circuit scale becomes large. [0007] A speed conversion circuit according to the present invention is used for various devices of the ATM system. In the AAL unit on the protocol, the transmission cell head signal and the reception cell head signal are asynchronous. SA to accommodate different line speeds in case
The R unit has a reception bit conversion unit that converts the data width of a cell received from the line side, and a read start point switching circuit that switches the read start timing according to the line speed, and is converted by the reception bit conversion unit. A reception memory unit for storing cell data, a message assembling control unit which is activated by a read start timing from a read start point switching circuit, transfers cell data from the reception memory unit to an external memory unit, and assembles a message; A transmission memory unit having a write start point switching circuit for switching the write start timing according to the speed, and a write start timing from the write start pointer switching circuit, which is activated by the write start timing, and transfers a message from the external memory unit to the transmission memory unit by dividing the message into cells. Cell division control unit and transmission memo A transmission bit conversion unit that converts the data width of a transmission cell from the unit and transmits the data to the line side; a message assembly control unit for an external memory unit; a cell division control unit; and an interface unit that arbitrates a memory access request from an external device. And the interface unit comprises:
The message assembly control unit and the cell division control unit
If there are simultaneous access requests with the same priority,
Alternate message assembly controller and cell division controller
To access the message assembly control unit and cell
When there is no memory access request from the
The configuration is such that an access request from the external device can be made . In the speed conversion circuit having the above configuration, the data width of the cell received from the line in synchronization with the cell head signal is converted by the reception bit conversion unit and stored in the reception memory unit. The read start point switching circuit in the reception memory unit outputs a read start timing corresponding to the line speed to the message assembling control unit. Upon receiving the read start timing, the message assembly control unit
The cell data is transferred from the receiving memory unit to the external memory unit and a message is assembled. On the other hand, a write start point switching circuit in the transmission memory outputs a write start timing corresponding to the line speed to the cell division control unit. Upon receiving the write start timing, the cell control unit divides the message into cells from the external memory unit and transmits the message to the transmission memory unit. The data width of the transmission cell from the transmission memory unit is converted by the transmission bit conversion unit and transmitted to the line side. Interface unit, message assembly controller, have rows arbitrates memory access requests from the cell division control unit and an external device, a message assembly control unit and the cell fraction
Access request at the same priority with the
The message assembly control unit and cell division
Access to each other alternately to control the assembly of these messages.
There is no memory access request from the control unit and the cell division control unit.
Access request from an external device is enabled . Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of the present invention. In FIG. 1, the SAR unit 10 has an 8-bit
A / 32-bit conversion unit 11, a reception FIFO unit 12, a message assembly control unit 13, a cell division control unit 14,
Transmission FIFO unit 15 and 32-bit / 8-bit conversion unit 1
6 and an INF (interface) unit 17. In the SAR unit 10, 8 bits / 3
The 2-bit conversion unit 11 includes a flip-flop and a reception FI
And a circuit for decoding the lower 2 bits of the read address from the FO unit 12, and converts the data width of the received cell from 8 bits to 32 bits. The receiving FIFO unit 12 has a 32-bit width F
It comprises an IFO memory unit 12a and a read start point switching circuit 12b. As shown in FIG. 2, the read start point switching circuit 12b includes an address counter 21 that counts up by the line clock and a write start address given from the address counter 21 to several read start points that have been calculated in advance. A decoder 22 for decoding correspondingly, and a register 23 for setting a line-side speed based on a signal from a higher order
And a selector 24 for selecting a decode value of the decoder 22 in accordance with the line speed set in the register 23, and notifies the message assembling control unit 13 of the selected signal as read start timing. The message assembling control unit 13 is composed of a read address counter which counts up by an internal clock in accordance with the message assembling process, and other control circuits, and is provided from when a read start timing from the reception FIFO unit 12 is set. Start message assembly processing. The cell division control unit 14 includes a write address counter that counts up by an internal clock in accordance with the cell division processing, and other control circuits. When the write start timing from the transmission FIFO unit 15 is set, the cell division control unit 14 starts the cell division processing. Start. The transmission FIFO unit 15 has a 32-bit width F
It comprises an IFO memory unit 15a and a write start point switching circuit 15b. As in the read start point switching circuit shown in FIG. 2, the write start point switching circuit 15b pre-calculates an address counter 21 that counts up with the line clock and a read address given from the address counter 21. A decoder 22 for decoding in accordance with some of the write start points, a register 23 for setting a line speed based on a signal from a higher-order device, and a register 23 for adjusting the line speed set in the register 23. Decoder 22
And a selector 24 for selecting a decode value of the selected signal. The selected signal is notified to the cell division control unit 14 as a write start timing. The 32-bit / 8-bit conversion section 16 is constituted by a flip-flop and a circuit for decoding the lower 2 bits of the write address from the transmission FIFO section 15, and converts the data width of the transmission cell from 32 bits to 8 bits. . The INF section 17 is an interface section with the external memory section 31 and performs arbitration when external message access requests from the upper CPU section 32 of the message assembly control section 13 and the cell division control section 14 overlap. The external memory unit 31 is equivalent to a single port memory. FIG. 3 shows a cell format. As is clear from the figure, (a) GFC (Gener
ic Flow Control; VPI (Virtual
Path Identifier (virtual path identifier), (b) VPI,
Information such as (C) VCI (Virtual Channel Identifier), (d) PT (Payload Type), and (e) CLP (Cell Loss Priority) is stored. FIG. 4 shows the relationship between the cell flow and the message. Next, the operation of the SAR unit 10 having the above configuration will be described with reference to the time charts of FIGS. Note that, in the time charts of FIGS. 5 and 6, the cell flow to corresponds to the cell flow in FIG. 1, respectively. Further, the SAR unit 10 according to the present embodiment includes:
It is assumed that the cycle of the cell head signal can correspond to the cell flow in the range of 132 ms to 2.7 μs. First, a cell received from the line in synchronization with the cell head signal has a data width of 8 bits / 32 bits.
The conversion unit 11 converts the data from 8 bits to 32 bits, and the reception FIFO unit 12 stores the data in the FIFO memory unit 12 having a width of 32 bits.
a. Read start point switching circuit 12b
Has several types of read start points (values obtained by decoding write addresses) corresponding to the line speed in the decoder 22, and selects them by the selector 24 based on the value set in the register 22. The read start timing is output to the message assembling control unit 13 when the write address has advanced to this point. When the message assembling control unit 13 receives the read start timing from the read start point switching circuit 12b, it first reads the header of the cell from the reception FIFO unit 12, and based on the VPI / VCI in the header, reads out the header of the cell. The control information and the information for assembling the message are read from the external memory unit 31, and an address for storing the cell is extracted based on the information (preprocessing). Then, the payload section is transferred to the external memory section 31 and stored at the extracted address. Like the read start point switching circuit 12b, the write start point switching circuit 15b also has several types of write start points (decoded values of read addresses) corresponding to the line speeds in the decoder 22.
It is selected by the selector 24 based on the value set in the register 23, and when the read address has advanced to the decoded value, the write start timing is output to the cell division control unit 14. Upon receiving the write start timing from the write start point switching circuit 15b, the cell division control unit 14 controls the external memory unit 31 based on the header information (VPI / VCI) of the cell to be transmitted received from the CPU unit 32. Extract the information and the address where the message is stored. Then, the first 48 bytes of the message in the external memory unit 31 are read, and the message is added to the header and stored in the 32-bit FIFO memory unit 15 a in the transmission FIFO unit 15. The stored cell is read out in accordance with the cell-side signal on the line side, and is read out in 32 bits / 8 bits.
After it is converted from 32 bits to 8 bits by the it conversion unit 16, it is transmitted to the line side. The INF unit 17 arbitrates memory access requests from the message assembly control unit 13, the cell division control unit 14, and the upper CPU unit 32. The message assembling control unit 13 and the cell division control unit 14 have the same priority, and if there is an access request at the same time, they can be accessed alternately. The upper CPU unit 32
Is lower in priority than the message assembly control unit 13 and the cell division control unit 14.
Access can be made only when there is no access request from. The INF unit 17 based on such priorities
When the message assembling process and the cell dividing process overlap due to the arbitration of the memory access request by, the processing time becomes 1280 ns as shown in (1) of FIG.
If the message assembling process and the cell dividing process do not overlap, as shown in (2) of FIG.
It happens that s becomes shorter. As described above in detail, according to the present invention, the transmission / reception FIFO unit has a function of absorbing the speed difference from the line side and adjusting the SAR processing time difference and timing. With this configuration, the buffer unit conventionally used to match the timing of internal processing can be deleted, so that the circuit scale (memory amount) can be reduced even when accommodating different line speeds.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing one embodiment of the present invention. FIG. 2 is a block diagram illustrating an example of a read / write start point switching circuit. FIG. 3 is a diagram showing a cell format. FIG. 4 is a diagram showing a relationship between a cell flow and a message. FIG. 5 is a time chart (part 1) for explaining a circuit operation according to the present invention; FIG. 6 is a time chart (part 2) for explaining a circuit operation according to the present invention; FIG. 7 is a block diagram showing a conventional example. FIG. 8 is a time chart (part 1) for explaining a circuit operation according to a conventional example. FIG. 9 is a time chart (part 2) for explaining a circuit operation according to a conventional example. [Description of Signs] 10 SAR unit 11 8-bit / 32-bit conversion unit 12 Reception FIFO unit 12a Read start point switching circuit 13 Message assembly control unit 14 Cell division control unit 15 Transmission FIFO unit 15a Write start point switching circuit 16 32-bit / 8-bit conversion unit 17 INF (interface) section 31 external memory section 32 upper CPU section

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-7-162433 (JP, A) IEICE Technical Report IN90-24 1994 IEICE Autumn Conference B-579 1995 IEICE General Conference B-756 IEICE Technical Report CS92-50 (58) Fields investigated (Int. Cl. ⁷ , DB name) H04L 12/56 H04L 13/08

Claims (1)

(57) [Claims 1] The heterogeneous line speed when the transmission cell head signal and the reception cell head signal in the AAL part on the protocol used in various devices of the ATM system are asynchronous. The receiving SAR unit includes a reception bit conversion unit that converts a data width of a cell received from the line side, and a read start point switching circuit that switches a read start timing according to a line speed. A receiving memory unit for storing the obtained cell data, and a message assembling control unit which is activated by a read start timing from the read start point switching circuit, transfers cell data from the receiving memory unit to an external memory unit, and assembles a message. Switch the write start timing according to the line speed A transmission memory unit having a circuit; a cell division control unit that is activated by a write start timing from the write start pointer switching circuit and divides a message into cells from the external memory unit to the transmission memory unit and transfers the divided cells; A transmission bit conversion unit for converting the data width of a transmission cell from the memory unit and transmitting the converted data to the line side; an arbitration of a memory access request from the message assembly control unit, the cell division control unit and the external device to the external memory unit the and an interface unit for performing, said interface unit, said message assembly control unit
And the cell division control unit at the same time with the same priority.
Access request, these message assembly control units
And the cell division control unit are accessed alternately, and these messages are
Memory access from the storage assembly control unit and the cell division control unit.
Access request from the external device when there is no access request.
Speed conversion circuit, characterized in that which enables determined.