1. overview

This section describes libraries for accessing files on CDs.

1.1 Features

This library has the following features.

(1) Target CD-ROM

1. ISO9660 level file access is possible.
2. This library does not cover access using CD-ROM XA subheader information.

(2) Data buffering

1. Access is performed assuming the CD block buffer management mechanism.
2. In addition to simple file reading, it is possible to read ahead using a buffer.

(3) File identifier

1. Access is based on file identifier (order number within the directory).
2. Eliminate the slowdown caused by directory searches. >
3. Access by file name is possible by using the file name to file identifier conversion function.

(4) Development support function

1. Memory files and DOS files can be accessed as a development support function.
2. If it is a small amount of data, a memory file can replace the file on the CD.
3. DOS files on IBM-PC can be accessed like memory files via SCSI.
   Even if the data is too large to fit in the SIMM, it can be used as a substitute for files on the CD.
4. We provide two types of libraries: one for product embedding and one that includes development support functions.

1.2 Functional overview

This section provides an overview of the functionality of the file system library. The functions of this library are classified into the following six types.

(1)Directory operations

It provides the following functions such as library initialization, reading directory information, and setting the current directory.

function	function
GFS_Init	Library initialization and CD mounting process
GFS_LoadDir	Load directory information
GFS_SetDir	Setting the current directory
GFS_NameToId	File name → file identifier conversion
GFS_IdToName	File identifier → file name conversion
GFS_GetDirInfo	Get directory information
GFS_Reset	Resetting the file system

(2) File operations

Perform common file operations such as opening, closing, and seeking files.

function	function
GFS_Open	Open file
GFS_Close	Close file
GFS_Seek	Moving the access point
GFS_Tell	Get access pointer
GFS_IsEof	Check if the access pointer is at the end of the file
GFS_ByteToSct	Conversion from byte to sector
GFS_GetFileSize	Get file size
GFS_GetFileInfo	Get file information
GFS_GetNumCdbuf	Obtaining the number of sectors in the CD buffer partition

(3) Completion return type reading

Read data from file. In this case, control will not return from the function until data loading is complete.

function	function
GFS_Fread	Reads data from the opened file.
GFS_Load	Reads data by specifying a file identifier.

(4) Immediate return type reading

The request and server functions read data from the file. The server function processes requests issued by the request function in processing units.
Server functions must be called repeatedly. By inserting application processing into the server function call loop, you can execute application processing until data loading is complete.

function	function
GFS_NwFread	Issuing a data load request
GFS_NwCdRead	Issuing a read request to the CD buffer
GFS_NwIsComplete	Check for completion of loading process
GFS_NwStop	Aborting the loading process
GFS_NwGetStat	Get access status
GFS_NwExecOne	Server function for one file
GFS_NwExecServer	Server functions for multiple files

(5) Reading parameter settings

Set various parameters for the completion return and immediate return read functions. You can change how to use the CD buffer, transfer method (DMA, CPU, etc.), and transfer unit.

function	function
GFS_SetGmode	Setting the ejecting method from the CD buffer
GFS_SetTmode	Transfer method settings
GFS_SetReadPara	Setting the reading unit to the CD buffer
GFS_SetTransPara	Transfer unit setting from CD buffer
GFS_SetTrFunc	Registering a transfer function
GFS_StartTrans	Transfer start in transfer function

(6) Others

Provides CD pickup control, error processing function registration, and error status acquisition functions. Error handling functions are called when an error occurs.

It also provides a CD-DA track number conversion function when using the DSS system.

function	function
GFS_CdMovePickup	Moving the CD pickup
GFS_SetErrFunc	Registering an error handling function
GFS_GetErrStat	Get error status
GFS_ConvTno	Track number conversion

1.3 Module configuration

Figure 1.1 shows the positioning of this library in relation to hardware and other software. The dotted lines are modules included in the debugging library.

Figure 1.1 Module configuration diagram

To use this library, you need to link the following libraries at the same time.

• SHCNPIC.LIB
  Library for SH7600 that does not support position independent code

• SEGA_CDC.LIB
  CD communication interface library

• SEGA_DMA.LIB
  DMA library

• SEGA_CSH.LIB
  cache library