JP2003330623A - External storage device and its data buffer control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an external storage device capable of quickly outputting ROM data and its data buffer control method. <P>SOLUTION: The microcomputer of an external storage device judges whether or not a leading address is stored in a data buffer configuring a data cache at the time of receiving a reading request for ROM data from a navigation AV device, and outputs ROM data stored in the data buffer when the leading address is stored, and abandons the data stored in the data buffer, and outputs the ROM data stored in the storage media to the navigation AV device, and buffers the data in the data cache when any leading address is not stored. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an external storage device having a data cache and a data buffer control method thereof.

[0002]

2. Description of the Related Art In recent years, for example, a car navigation device has a CD reader, a DVD reader, or a hard disk device, and can reproduce both ROM data and AV data stored in a CD, a DVD, or a hard disk. A navigation AV device provided with an external storage device is provided. In this type of external storage device, CD, DV
In order to improve the efficiency of reading data from the D or hard disk, read request data from the navigation AV device (host) is prefetched before being transferred to the navigation AV device and buffered in the data cache in the external storage device. At the same time, the data stored in the data cache is sequentially output to the outside to increase the data transfer rate from the external storage device to the host.

[0003]

By the way, when the data from the external storage device to the car navigation AV device is AV data, it is common to transfer the data to the host at consecutive ascending addresses starting from a certain address. is there.
The buffer control for data transfer at that time buffers the data from the start address requested from the external device to the data cache, outputs the data from the data cache to the car navigation AV device, and when the output is completed, new data is output. The predominant control is read-ahead control such as buffering.

On the other hand, when the transfer data is ROM data, the data is often requested from the outside at random, and the data once output to the outside is often requested again from the outside. Therefore, when reading the ROM data, if the same read control as that of the AV data is used, the reading must be performed every time. In this case, since the reading of data involves mechanical movement of the head, the responsivity of rereading the data decreases, and at the same time, quality problems such as head durability and moving noise occur.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an external storage device and a data buffer control method therefor capable of increasing the output speed of ROM data.

[0006]

According to the invention of claim 1, when AV data is output from the storage means to the host in response to a read command from the host, the AV data is prefetched and buffered in the data cache. Then, the AV data output speed can be increased by outputting the AV data to the host.

On the other hand, when the ROM data is output from the storage means to the host, the ROM data is buffered in the data cache, and when the host next requests the ROM data stored in the data cache, the ROM data is stored. Outputs data from the data cache to the host. As a result, it is not necessary to read the ROM data from the storage means, so that the output speed of the ROM data and thus the reading speed by the host can be increased. Where RO
When the M data is not stored in the data cache, the ROM data is output from the storage means to the host and buffered in the data cache, so that the next read can be performed.

According to the second aspect of the present invention, when the ROM data requested by the host does not exist in the data cache, the ROM data stored in the data cache is discarded and the ROM data is stored in the storage means. It reads and outputs to the host and buffers in the data cache.

If there is a free space in the data cache, the ROM data following the ROM data is prefetched and buffered until the data cache is full. This makes it possible to speed up reading of continuous ROM data.

According to the third aspect of the present invention, if some of the ROM data requested by the host is present in the data cache, the ROM data is read from the storage means. RO that exists in the data cache cannot be increased in speed.
It outputs M data to the host and discards other ROM data buffered in the data cache. Then, the remaining ROM data is read from the storage means, output to the host, and buffered in the data cache. As a result, the reading speed of ROM data can be increased. Further, when the data cache becomes full, the ROM data transmitted to the host is discarded and the remaining ROM data is buffered there, so that the latest ROM data can be buffered in the data cache.

According to the fourth aspect of the present invention, the control means, when the ROM data is read from the storage means and the ROM data is stored in the data cache, the RO means.
The M data is output to the host, and when the ROM data is not stored, the ROM data is output from the storage means to the host and buffered in the data cache, so that the reading of the ROM data by the host can be speeded up. it can.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment in which the present invention is applied to an external storage device of a car navigation system will be described below with reference to FIGS. FIG. 1 is a block diagram schematically showing a car navigation system. In FIG. 1, the navigation AV device 1 and the external storage device 2 are mounted on a vehicle, and when the navigation AV device 1 as a host issues a data read request, the external storage device 2 receives the commanded data. Is read from the data storage device 3 and output to the navigation AV device 1. The external storage device 2 is a DVD drive, a CD drive,
In the present embodiment, a D that can reproduce a CD, such as an HDD, is used.
The data storage device 3 which is a VD drive and is a storage means is a DVD or a CD (hereinafter referred to as a storage medium). There are two types of data output from the external storage device 2 to the navigation AV device 1, that is, continuous AV data such as music data and non-continuous ROM data such as map data for car navigation. Can be distinguished. In this case, only one of the AV data and the ROM data is stored in the storage medium 3, and the AV data and the ROM data may be stored together in the HDD.

The external storage device 2 comprises a read head 4, an amplifier 5, a servo 6, a microcomputer 7, a data processing unit 8, a data cache 9 and an interface 10. The microcomputer 7 as a control unit optimally drives the servo 6 for driving the read head 4 based on the output result of the amplifier 5, thereby irradiating the storage medium 3 with laser light in a spot shape, and the read head 4 is read. The data stored in the storage medium 3 is read according to the amount of reflected light received by the. The data processing unit 8 binarizes the analog signal output from the amplifier 5 and outputs it to the navigation AV device 1 through the interface 10.

The data cache 9 is a DRAM or SRA.
The microcomputer 7 controls the data processing section 8 to control the operation of the data cache 9 as described later. This data cache 9
2 is composed of N block buffers, and the data capacity per block is arbitrary (generally, several K to several tens of K bytes).

Next, the operation of the above configuration will be described. FIG. 3 shows the ROM / AV data reproduction discrimination operation of the microcomputer 7. In FIG. 3, when the microcomputer 7 is activated, it discriminates the built-in disc and discriminates between the navigation storage medium and the music storage medium. The ROM reproduction mode is set for the navigation storage medium, and the AV reproduction mode is set for the music storage medium.

Now, in order for the user to listen to music, the music C
When D is set, the microcomputer 7 determines that it is a storage medium for music and sets the AV reproduction mode. Then, the read request from the sector address in which the music set by the user (usually the first music) is stored is output to the external storage device 2.

Here, when the navigation AV device 1 outputs a read request for the data stored at a predetermined address of the storage medium 3 to the external storage device 2, the microcomputer 7 of the external storage device 2 causes the navigation AV device 1 to operate. The data instructed by the command is output to the data cache 9 and the data following the data is prefetched from the storage medium 3 and buffered. Such a buffer operation is performed during or after the output of data to the navigation AV device 1.

When a command to read the next data is received from the navigation AV device 1, the external storage device 2
Of the data cache 9 outputs the next data stored in the data cache 9 to the navigation AV device 1 and discards the data that has been output to the data cache 9
The data subsequent to the final data stored in is read ahead from the storage medium 3 and buffered.

By the above operation, the navigation AV device 1 can continuously reproduce the music data input from the external storage device 2, so that the music desired by the user can be reproduced. In this case, since continuous data is prefetched from the storage medium 3 and buffered in the data cache 9, the music data is surely reproduced even when the access of the read head 4 is slow or the access fails. can do. On the other hand, when the user sets the navigation DVD to use the car navigation, the microcomputer 7 determines that the navigation storage medium is set, and sets the ROM reproduction mode.

Here, the navigation AV device 1 is started by reading the system from the storage medium 3, finds the current position by the GPS system, and displays the map including the current position on the external storage device 2 in order to display the map on the display. The external storage device 2 is instructed to use the sector address of the predetermined map data stored in the memory as read request data.

In this case, the microcomputer 7 of the external storage device 2
When the leading block of the read request data from the navigation AV device 1 is not present in the data buffer, reads all of the read request data from the storage medium 3 and buffers the data in the data cache 9.

Specifically, as shown in FIG. 4, the data cache 9 of the external storage device 2 has a storage medium 3003 3003.
When there is a read request for two blocks from the navigation AV device 1 to 30020h to 3003Fh while the data of 0h to 3008Fh is stored, the microcomputer 7 determines whether the data of the head address exists in the data buffer. If it does not exist, all the data in the data buffer is discarded, and then the data is stored in the addresses 30020h to 3003Fh of the storage medium 3 from the top of the physical address of the data buffer (indicated by buffer 0 in the figure) The existing data is prefetched and buffered in the data cache 9. At the same time, address 30020h ~
The ROM data of 3003Fh is transferred to the navigation AV device 1. In this case, when pre-reading is executed during data transfer to the navigation AV device 1, data transfer and pre-reading are performed in parallel.

As a result of the above operation, the navigation AV apparatus 1 has the address 30 which is read request data.
ROM data of 020h to 3003Fh will be transferred, and map data or map information indicated by those ROM data can be displayed.

Here, the microcomputer 7 determines whether or not the data buffer forming the data cache 9 has a free space. In this case, since there is free space in the data buffer,
Data is prefetched and buffered from address 30040h until the data buffer is full. As a result of the above-described operation, the data cache 9 finally has ROs from addresses 30020h to 3007Fh.
There will be M data in the buffer.

Unlike AV data, ROM data may be read continuously in the order in which they are stored, or the same ROM data may be read again. Therefore, in the present embodiment, when the navigation AV device 1 issues an instruction to read ROM data, it is determined whether the ROM data is stored in the data buffer. If so, the microcomputer 7 The ROM data stored in the data buffer is transferred to the navigation AV device 1. As a result, the data can be output to the navigation AV device 1 without directly accessing the ROM data stored in the storage medium 3, so that the reading speed of the navigation AV device 1 with respect to the external storage device 2 can be increased. You can

On the other hand, when the vehicle advances, the navigation AV device 1 may request the next map information from the external storage device 2 in order to display the map information following the current map information. In such a case, when the next map information is stored at the address following the previously read map information, since the map information is read ahead and already stored in the data buffer, the microcomputer 7 The map information stored in the data buffer is output to the navigation AV device 1. As a result, the map information can be read out faster than when the map data is read out from the storage medium 3.

By the way, when the navigation AV device 1 requests the transfer of the number of blocks exceeding the number of data buffers, the ROM data for the shortage is buffered while discarding the data already transferred by the same command. In this case, prefetching of data after the request end sector address is not performed.

Specifically, while the data cache 9 as shown in FIG. 5 is stored for 6 blocks before the transfer request, the read request address is 30030h to 300.
If it is AFh, the data buffer has address 30
Since the data of 030h to 3005Fh exists, the data of 3000h to 3002 which has already been transferred by the same command.
Address 30030 while discarding data up to Fh
Navigation AV device 1 for data of h to 3005Fh
Output to.

Addresses 30030h to 3005
When the output of Fh data to the navigation AV device 1 is completed, the subsequent addresses 30060h to 300AFh
Read the data up to. In this case, the data buffer functions as a ring counter, and for the addresses 30090h to 300AFh that exceed the data buffer size, the data at the head addresses 30030h to 3004Fh are discarded and then buffered there. in this case,
No prefetch after data buffering is performed. That is, only the deficient portion of the read request data is newly buffered, and finally, the latest data of 30050h to 300AFh exists in the data buffer.

According to such an embodiment, when the external storage device 2 receives a ROM data read command from the navigation AV device 1, it determines whether data exists in the data cache 9 and exists. In that case, the data is output, and when it does not exist, the ROM data stored in the storage medium 3 is output and the ROM data is buffered in the data cache 9. Therefore, when the ROM data is read again, the storage is performed. Unlike the conventional example in which it is necessary to read from the medium one by one, the number of times the head 4 is mechanically driven can be suppressed, and the read speed of ROM data can be increased.

Moreover, when the ROM data is stored in the data cache 9, the subsequent ROM data is prefetched and buffered in the data cache 9, so that it is not limited to the already read ROM data but continuous RO.
It is possible to speed up the reading of even M data.

The present invention is not limited to the above embodiment, but can be modified or expanded as follows. When the external storage device 2 is an HDD and both AV data and ROM data are stored, the external storage device 2 receives the data output request from the navigation AV device as shown in FIG. The type of the request data may be discriminated, and the ROM reproduction mode may be set when the request data is ROM data, and the AV reproduction mode may be set when the request data is AV data.

[Brief description of drawings]

FIG. 1 is a block diagram showing an electrical configuration of an external storage device according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a data cache.

FIG. 3 is a flowchart showing a startup operation of a microcomputer of an external storage device.

FIG. 4 is an explanatory diagram showing a control operation of a data cache.

FIG. 5 is an explanatory diagram showing different control operations of the data cache.

FIG. 6 is a view corresponding to FIG. 3 showing another embodiment of the present invention.

[Explanation of symbols]

1 is a navigation AV device (host), 2 is an external storage device, 3 is a data storage device (storage means), 7 is a microcomputer (control means), and 9 is a data cache.

Claims (4)

[Claims] 1. When data is output from a storage means to a host in response to a read command from the host, the data is prefetched and buffered in a data cache, and the stored data is output to the host to save the data. In a method of controlling a data buffer of an external storage device, the output speed of which is increased, when the ROM data is stored in the data cache when the ROM data is read from the storage means, the ROM data is output to the host. , The ROM
A data buffer control method for an external storage device, wherein when the data is not stored, the ROM data is output from the storage means to the host and buffered in the data cache. 2. When the ROM data requested by the host does not exist in the data cache, the ROM data buffered in the data cache is discarded, and then the ROM data is read from the storage means. When the data is output to the host and is buffered in the data cache, and when there is a free space in the data cache, the ROM data following the ROM data is prefetched and buffered until the data cache is full. The data buffer control method of an external storage device according to claim 1. 3. The RO existing in the data cache when a part of the ROM data requested by the host exists in the data cache.
After outputting M data to the host and discarding other ROM data buffered in the data cache, the remaining ROM data is read from the storage means and output to the host and buffered in the data cache. 2. The external storage device according to claim 1, wherein when the data cache is full, the ROM data transmitted to the host is discarded and the remaining ROM data is buffered therein. Data buffer control method. 4. An external storage comprising a storage means, a data cache, and a control means for pre-reading read request data from the host from the storage means, outputting the data to the host and buffering the data in the data cache. In the device, the control unit outputs the ROM data to the host when the ROM data is stored in the data cache when reading the ROM data from the storage unit, and the ROM data is stored. An external storage device, characterized in that when not present, the ROM data is output from the storage means to the host and buffered in the data cache.