JP2009217511A - Common bus controller and its control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that when there is an access request to a second device when a first device of a plurality of devices using a common bus uses a bus, completion of the first device is awaited or the access needs to be interrupted. <P>SOLUTION: A common bus controller has a plurality of bus switches 104 to 107 which are connected to a control bus and a data bus between a host controller 101 and a plurality of devices 102 and 103 and interrupt or connect a bus in accordance with a control signal from the host controller. By switching connection of the bus switch connected to an unused bus to connection to another device according to a control signal from the host controller, an access becomes available between the host controller and the plurality of devices. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a shared bus control device that connects a plurality of devices and a host controller via a shared bus, and a control method therefor.

  Conventionally, there is a storage medium (hereinafter referred to as a storage medium) in which a flash memory is used as a storage device and a controller of the storage device is built in, and such a storage medium is used as a storage medium for imaging data such as a digital still camera. Yes. Typical examples of these storage media include a compact flash (registered trademark) card, an SD card, and a memory stick card. There are detailed standards for the interface between these storage media and the host controller (data read and write to the storage media) for each storage medium.

  On the other hand, in the host controller that interfaces with these storage media, it is necessary to prepare a communication system according to the standard of the storage media and a controller according to the electrical characteristics.

Here, it has been proposed to reduce the cost by connecting the host controller / storage medium interface bus and the I / O device outside the host controller as a common bus, and sharing the controller, bus, and terminals. . At this time, the storage medium and the I / O device are exclusively accessed, and the storage medium and the I / O device can be electrically separated from each other by a bus switch or the like. For example, when the host controller is accessing an I / O device, the storage media is inactive by electrically disconnecting it with a bus switch connected to the storage media so that it does not malfunction. Need to control. The configuration of this bus switch is described in Patent Document 1. When the common bus is used exclusively, the devices that use the bus are electrically connected, while the devices that are not used are electrically disconnected, so that the devices do not affect each other. Need to do.
JP-A-10-283309 Japanese Examined Patent Publication No. 2-170256

  When such a common bus configuration is adopted, for example, when the host controller reads a file from a storage medium, the reading is performed by DMA (direct memory access). During this reading period, I / O devices connected by a common bus cannot be normally accessed until DMA ends and the bus switch is switched to the I / O device side. Therefore, when accessing the I / O device, it is necessary to wait for the end of the DMA or interrupt the DMA that is reading from the storage medium and switch the bus switch to the I / O device. Further, when reading the file from the storage medium is interrupted, when the storage medium is accessed again, the same file may need to be read from the beginning, resulting in problems such as poor data read efficiency. In addition, DMA interruption processing, bus switch switching, and the like are required, and the processing time becomes relatively long, so that there are cases where access to the I / O device is not in time.

  On the other hand, Patent Document 2 proposes a method in which a first device connected by a common bus is temporarily waited and electrically disconnected to enable access to the second device. However, this method has a problem that the first device cannot be accessed while the second device is being accessed.

  An object of the present invention is to solve the above-mentioned conventional problems.

  According to an aspect of the present invention, the unused bus connection is switched to the second device while accessing the first device. Accordingly, it is possible to provide a common bus control device and a control method thereof that enable access to the second device even while accessing the first device.

In order to achieve the above object, a common bus control device according to an aspect of the present invention has the following configuration. That is,
A shared bus control device for connecting a plurality of devices and a host controller via a shared bus,
A plurality of bus switches connected to each of a control bus and a data bus between each of the host controller and the plurality of devices, and disconnecting or connecting the bus according to a control signal from the host controller;
The host controller enables access between the host controller and a plurality of devices by switching the connection of a bus switch connected to an unused bus to a connection with another device by the control signal. It is characterized by that.

In order to achieve the above object, a control method for a common bus control device according to an aspect of the present invention includes the following steps. That is,
A plurality of bus switches that are connected to a control bus and a data bus between the host controller and each of the plurality of devices, and that disconnect or connect the bus according to a control signal from the host controller; A control method of a shared bus control device for connecting the plurality of devices and the host controller via:
By switching the connection of the bus switch connected to the unused bus to the connection with another device by the control signal from the host controller, the host controller and the plurality of devices can be accessed. It is characterized by that.

  According to the present invention, the connection of the unused bus is switched to the second device while accessing the first device, so that the second device can be accessed even while the first device is being accessed. There is an effect that can be accessed.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments do not limit the present invention according to the claims, and all combinations of features described in the present embodiments are essential to the solution means of the present invention. Not exclusively.

  FIG. 1 is a block diagram showing an example of a shared bus control device using a storage medium and an I / O device as a common bus according to an embodiment of the present invention.

  A microcomputer 100 includes a host controller 101 that can access a storage medium (first device) 102 and an I / O device (second device) 103. The host controller 101 is a controller having a specification that satisfies the requirements of the communication method and electrical characteristics according to the standard of the connected storage medium. The CPU 110 is a CPU built in the microcomputer 100, and controls the host controller 101, a bus switch to be described later, and the like according to a program stored in the memory 111. The storage medium 102 can write data to and read data from a flash memory built in the storage medium 102 by communicating with the host controller 101 in accordance with the standard of the storage medium 102.

  The host controller 101 and the storage medium 102 according to the present embodiment interface with a command bus (control bus) (CMD), a data bus (DAT [3: 0]), and a clock (CLK) (not shown). A bus switch 104 and a bus switch 105 are provided between the host controller 101 and the storage medium 102, and the command bus and the data bus can be electrically connected / disconnected by the bus switches 104 and 105. As for signals between the storage medium 102 and the bus switches 104 and 105, the command bus is represented by CMD_A, and the data bus is represented by DAT_A [3: 0].

  On the other hand, the I / O device (second device) 103 is connected by a common bus. Bus switches 106 and 107 are provided between the host controller 101 and the I / O device 103, and the bus switch 106 and 107 can be used to electrically connect / disconnect the command bus and the data bus. As for signals between the I / O device 103 and the bus switches 106 and 107, the command bus is represented by CMD_B, and the data bus is represented by DAT_B [3: 0].

  The bus switch 104 is electrically connected / disconnected by a control signal OE_A0 from the microcomputer 100. That is, the bus switch 104 is electrically connected when the control signal OE_A0 is at a high level, and is electrically disconnected when the control signal OE_A0 is at a low level. Similarly, the bus switch 105 is electrically connected when the control signal OE_A1 is at a high level, and is electrically disconnected when the control signal OE_A1 is at a low level.

  Similarly, the bus switch 106 is electrically connected when the control signal OE_B0 is at a high level, and is electrically disconnected when the control signal OE_B0 is at a low level. Further, the bus switch 107 is electrically connected when the control signal OE_B1 is at a high level, and is electrically disconnected when the control signal OE_B1 is at a low level. The command buses CMD, CMD_A, CMD_B, data buses DAT [3: 0], DAT_A [3: 0], and DAT_B [3: 0] are connected to the power supply voltage via pull-up resistors. When disconnected, each goes high.

  Next, the interfaces of the host controller 101, the storage medium 102, and the I / O device 103 according to this embodiment will be described in detail with reference to the timing charts of FIGS.

  FIG. 2 is a timing chart for explaining the timing at which the host controller 101 reads data from the storage medium 102 by DMA.

  Regarding the bus switches 104 to 107, the control signals OE_A0 and OE_A1 are at a high level, and the control signals OE_B0 and OE_B1 are at a low level. Therefore, the bus switches 106 and 107 are electrically disconnected while the bus switches 104 and 105 are electrically connected. Therefore, the host controller 101 is connected to the storage medium 102 via the bus switches 104 and 105, and is disconnected from the I / O device 103.

  The host controller 101 issues a command 201 to the command bus CMD at the timing (2) in FIG. The command 201 is transmitted to the command bus CMD_A via the bus switch 104 as the same command signal as the command signal on the command bus CMD, and the storage medium 102 receives the command 201. This command 201 is a command for instructing reading of data from the storage medium 102 by DMA.

  On the other hand, at the timing of (4) in FIG. 2, a response command (RSP (DMA)) to the aforementioned DMA read command 201 is transmitted from the storage medium 102 to the host controller 101. When this response command RSP (DMA) is issued from the storage medium 102 to the command bus CMD_A, this command is transmitted to the command bus CMD via the bus switch 104, and the host controller 101 receives it. When the host controller 101 receives the response command in this way, data is read by DMA at the timings (7) to (13) in FIG. Here, the number of data (D0 to Dn) 203 specified by the DMA read command is transmitted from the storage medium 102 to the host controller 101 by DMA. The data 203 read at this time is transmitted from the storage medium 102 to the data bus DAT_A [3: 0], and is transmitted to the data bus DAT [3: 0] via the bus switch 105. In this way, the host controller 101 receives the data read from the storage medium 102 by DMA. When receiving the last data (Dn), the host controller 101 issues a reception completion command (CMD (STOP)) 204 at the timing of (13) in FIG. This is transmitted to the storage medium 102 as a command (stop command) that completes reception of the DMA.

  Thereby, the storage medium 102 receives the stop command 204 and issues a response (RSP (STOP)) 205 to the stop command 204 to the command bus CMD_A at the timing (15) in FIG. As a result, the host controller 101 receives the response 205 via the bus switch 104 and the command bus CMD, and completes the read DMA.

  The I / O device 103 cannot communicate with the host controller 101 during the period of reading data from the storage medium 102 by this DMA (period (1) to (16) in FIG. 2). That is, the command bus CMD_B and the data bus DAT_B [3: 0] are electrically disconnected from the command bus and the data bus of the host controller 101. At this time, the command bus CMD_B and the data bus DAT_B [3: 0] are maintained at a high level by a pull-up resistor.

  FIG. 3 is a timing chart for explaining the timing at which the host controller 101 reads data from the I / O device 103 by DMA.

  In this case, the control signal OE_A0 and OE_A1 are at the low level and the control signals OE_B0 and OE_B1 are at the high level, in contrast to the above-described barout in FIG. For this reason, the bus switches 104 and 105 are electrically disconnected, and the bus switches 106 and 107 are electrically connected. Therefore, the host controller 101 is connected to the I / O device 103 and disconnected from the storage medium 102.

  Now, the host controller 101 issues a command (CMD (DMA)) 301 to the command bus CMD at the timing of (2) in FIG. The command 301 is transmitted to the command bus CMD_B via the bus switch 106, and the I / O device 103 receives the command 301. This command 301 is a command for instructing to read data from the I / O device 103 by DMA. Next, at the timing of (4) in FIG. 3, the I / O device 103 issues a response 302 to the command 301 to the command bus CMD_B. This response 302 is sent to the host controller 101 via the bus switch 106 and the command bus CMD. When the host controller 101 receives the response 302 in this way, data 303 is transmitted from the I / O device 103 to the host controller 101 by DMA at the timings (7) to (13) in FIG. Here, the number of data (D0 to Dn) 303 specified by the command 301 is transmitted to the host controller 101. The data 303 is output from the I / O device 103 to the data bus DAT_B [3: 0], and is input to the host controller 101 via the bus switch 107 and the data bus DAT [3: 0].

  When the host controller 101 receives the last data (Dn), it issues a stop command (CMD (STOP)) 304 to the command bus CMD at the timing (13) in FIG. The I / O device 103 receives the stop command 304 via the command bus CMD, the bus switch 107, and the command bus CMD_B. Then, at the timing of (15) in FIG. 3, a response 305 to the stop command 304 is issued to the command bus CMD_B. As a result, the host controller 101 receives the response 305 via the bus switch 106 and the command bus CMD, and the read DMA is completed.

  During this period (period (1) to (16) in FIG. 3), the storage medium 102 cannot communicate with the host controller 101. The command bus CMD_A and the data bus DAT_A [3: 0] are electrically disconnected from the host controller 101 bus. Therefore, the command bus CMD_A and the data bus DAT_A [3: 0] are maintained in the high level state by the pull-up resistors.

  FIG. 4 is a timing diagram illustrating a state in which the host controller 101 accesses the I / O device 103 while the host controller 101 is reading data from the storage medium 102 by DMA.

  At timing (1) in FIG. 4, the control signals OE_A0 and OE_A1 are at a high level, and the control signals OE_B0 and OE_B1 are at a low level. For this reason, the bus switches 104 and 105 are electrically connected, and the bus switches 106 and 107 are electrically disconnected. Therefore, the host controller 101 is connected to the storage medium 102.

  The host controller 101 issues a read DMA command (CMD (DMA)) 401 to the storage medium 102 to the command bus CMD at the timing (2) in FIG. This command 401 is sent to the storage medium 102 via the bus switch 104 and the command bus CMD_A. Then, at the timing of (4) in FIG. 4, the storage medium 102 issues a response (RSP (DMA)) 402 to the command bus CMD_A. As a result, the host controller 101 receives the response 402 from the storage medium 102. Then, from the timing of (7) in FIG. 4, the host controller 101 starts receiving data from the storage medium 102 by DMA.

  Next, consider a case where a situation occurs in which the host controller 101 wants to access the I / O device 103 at the timing during the DAM transfer in (7) of FIG. In this case, the control signal OE_A0 is switched to the low level and the control signal OE_B0 is switched to the high level at the timing of (7) in FIG. As a result, the bus switch 104 connected to the unused command bus CMD is disconnected, and the bus switch 106 is connected instead. Thus, the command bus CMD is connected to the command bus CMD_B of the I / O device 103 via the bus switch 106, and disconnected from the command bus CMD_A of the storage medium 102.

  On the other hand, the data bus DAT [3: 0] of the host controller 101 is disconnected from the data bus DAT_B [3: 0] of the I / O device 103, and the data bus DAT_A [3: 0] of the storage medium 102 is disconnected. Remains connected. Therefore, during the period from (7) to (11) in FIG. 4, the host controller 101 can access the I / O device 103 using the command bus CMD while receiving data from the storage medium 102 by DMA.

  In this way, a command (CMD (IO)) 403 is issued to the I / O device 103 at timing (8) in FIG. 4, and a response (RSP (IO)) 404 is received at timing (10) in FIG. Can receive. When the host controller 101 receives the last data (Dn) from the storage medium 102, it issues a stop command (CMD (STOP)) 405 to the command bus CMD at the timing of (13) in FIG. Then, at the timing of (15) in FIG. 4, the storage medium 102 issues a response 406 to the stop command 405 to the command bus CMD_A. As a result, the host controller 101 receives the response 406 via the bus switch 104 and the command bus CMD, and the read DMA from the storage medium 102 is completed.

  Thus, for example, when the I / O device 103 is a stepping motor controller, it may be desired to access the I / O device 103 to perform speed control of the motor at a certain time. Even in such a case, it is possible to access the I / O device 103 without stopping the reading of data from the storage medium 102 by DMA.

  Next, referring to FIG. 5, as described with reference to FIG. 4, control for accessing the I / O device 103 while the host controller 101 is performing a DMA read from the storage medium 102 will be described.

  FIG. 5 is a flowchart for explaining processing by the host controller 101 according to this embodiment. A program for executing this processing is stored in the memory 111, and this processing is executed under the control of the CPU 110.

  First, in step S501, the CPU 110 instructs the host controller 101 to start reading data from the storage medium 102 by DMA. Next, in step S502, the CPU 110 determines whether an access request to the I / O device 103 has occurred during reading of data from the storage medium 102 (during DMA transfer). If there is no access request to the I / O device 103, the process proceeds to step S505, and it is determined whether or not the data read by the DMA transfer is completed. If the DMA transfer ends here, the process proceeds to step S506 to end the process.

  On the other hand, if there is an access request to the I / O device 103 in step S502, the process proceeds to step S503, and the host controller 101 measures the time from when the read DMA is started until the next command is issued. The next command is a stop command, which is issued at the timing of (13) in FIG. At this timing, the I / O device 103 cannot be accessed. Therefore, the time required to access the I / O device 103 is compared with the time required to issue the next command (stop command) during DMA. Based on the comparison result, it is determined whether or not the time interval (period) required for accessing the I / O device 103 is in time for the next command (stop command) to be issued in the currently executing DMA. judge. If it is determined here that the command of the I / O device 103 can be issued (in time), the process proceeds to step S504, where the I / O device 103 is accessed. On the other hand, if it is determined in step S503 that it is impossible, the process proceeds to step S505 to wait for the end of the DMA transfer.

  In step S504, as described with reference to FIG. 4 described above, the bus switch 104 is disconnected and the bus switch 106 is connected. Then, the command is issued from the host controller 101 to the I / O device 103 via the command bus CMD, the bus switch 106, and the command bus CMD_B.

  Here, FIGS. 4 and 5 show an example in which the I / O device 103 is accessed while data is being read from the storage medium 102 by DMA. However, the I / O device 103 can be similarly accessed while data is being written to the storage medium 102 by DMA.

  On the other hand, it will be easily understood that even when a command is issued to the storage medium 102 while the I / O device 103 is accessed by DMA, the command can be executed in the same manner.

  In the embodiment of FIGS. 4 and 5, the number of I / O devices 103 is one. However, even if there are two or more I / O devices 103, they can be controlled by the same bus switch. it can.

[Embodiment 2]
FIG. 6 is a diagram illustrating the configuration of the shared bus control device according to the second embodiment of the present invention. In FIG. 6, parts common to those in FIG. 1 are denoted by the same symbols, and description thereof is omitted.

  FIG. 6 shows an example in which the bus switches 104 to 107 in FIG. 1 are mounted inside the I / O device 601.

  In FIG. 6, the command bus and data bus controlled by the bus switches 104 and 105 pass through the I / O device 601 and are connected to the storage medium 102. The command bus and data bus controlled by the bus switches 106 and 107 are connected to, for example, a stepping motor controller 602 built in the I / O device 601.

  According to the configuration shown in FIG. 6, the bus switches 104 to 107 are provided in the I / O device 601, so that there is no need to provide the bus switch on the circuit board, which may be advantageous in terms of cost.

It is a block diagram which shows an example of the shared bus control apparatus which uses the storage medium and I / O device which concern on embodiment of this invention as a common bus. FIG. 6 is a timing chart for explaining the timing at which the host controller reads data from the storage medium by DMA in the embodiment of the present invention. FIG. 6 is a timing diagram for explaining the timing at which the host controller reads data from the I / O device by DMA in the embodiment of the present invention. FIG. 5 is a timing diagram illustrating a state in which the host controller accesses the I / O device while the host controller is reading data from the storage medium by DMA in the embodiment of the present invention. It is a flowchart explaining the process by the host controller which concerns on this Embodiment. It is a block diagram explaining the structure of the shared bus control apparatus which concerns on Embodiment 2 of this invention.

Claims (8)

A shared bus control device for connecting a plurality of devices and a host controller via a shared bus,
A plurality of bus switches connected to each of a control bus and a data bus between each of the host controller and the plurality of devices, and disconnecting or connecting the bus according to a control signal from the host controller;
The host controller enables access between the host controller and a plurality of devices by switching the connection of a bus switch connected to an unused bus to a connection with another device by the control signal. A shared bus control device characterized by that.   2. The sharing according to claim 1, wherein the host controller switches the bus switch so that a second device uses the control bus while a first device uses the data bus. Bus control device.   When an access request to the second device is generated while the first device is using the bus, the host controller determines a time interval until the first device uses the control bus next time. 3. The method according to claim 1, wherein whether or not to allocate the control bus to the second device is determined according to a result of comparing a time interval in which the second device uses the control bus. The shared bus control device described.   The host controller switches the bus switch so that a second device uses the control bus during a DMA transfer using the data bus by the first device. Shared bus controller. A plurality of bus switches that are connected to a control bus and a data bus between the host controller and each of the plurality of devices, and that disconnect or connect the bus according to a control signal from the host controller; A control method of a shared bus control device for connecting the plurality of devices and the host controller via:
By switching the connection of the bus switch connected to the unused bus to the connection with another device by the control signal from the host controller, the host controller and the plurality of devices can be accessed. A control method for a shared bus control device.   6. The sharing according to claim 5, wherein the host controller switches the bus switch so that a second device uses the control bus while the first device uses the data bus. Control method of bus control device. When an access request to the second device is generated while the first device is using the bus, the host controller determines a time interval until the first device uses the control bus next time. Comparing the time interval for the second device to use the control bus;
7. The shared bus control device control method according to claim 5, wherein whether to allocate the control bus to the second device is determined according to the comparison result.   The host controller switches the bus switch so that a second device uses the control bus during a DMA transfer using the data bus by the first device. Control method for shared bus control device.

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