1. 1. Overview

This section describes the library for accessing files on the CD.

1.1 Features

This library has the following features.

(1) Target CD-ROM

1. ISO9660 level file access is possible.
2. Access using the subheader information of CD-ROM XA is not covered by this library.

(2) Data buffering

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

(3) File identifier

1. Access by file identifier (sequential number in the directory) is the basis.
2. Eliminates slowdowns 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. You can access memory files and DOS files as a development support function.
2. If you have a small amount of data, you can replace the file on the CD with a memory file.
3. You can access DOS files on your IBM-PC via SCSI as well as memory files.
   Files on CD can be replaced even if the data is too large to fit in SIMM.
4. We provide two types of libraries, one for product embedding and one with development support functions.

1.2 Functional overview

This section outlines the features of the file system library. The functions of this library are classified into the following 6 types.

(1) Directory operation

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

function	function
GFS_Init	Library initialization and CD mounting process
GFS_LoadDir	Read directory information
GFS_SetDir	Current directory settings
GFS_NameToId	File name → file identifier conversion
GFS_IdToName	File identifier → file name conversion
GFS_GetDirInfo	Get directory information
GFS_Reset	File system reset

(2) File operation

Performs the following common file operations, such as opening, closing, and seeking files.

function	function
GFS_Open	Open file
GFS_Close	File close
GFS_Seek	Move access pointer
GFS_Tell	Get access pointer
GFS_IsEof	Check if the access pointer is at the end of the file
GFS_ByteToSct	Byte-by-sector conversion
GFS_GetFileSize	Get file size
GFS_GetFileInfo	Get file information
GFS_GetNumCdbuf	Get the number of sectors in the CD buffer partition

(3) Completion return type reading

Read data from a file. At this time, control does not return from the function until the data reading is completed.

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

(4) Immediate return type reading

Read data from a file with request and server functions. The server function processes the request issued by the request function for each processing unit.
Server functions must be called repeatedly. By inserting the application process into the server function call loop, the application process can be executed before the data loading is completed.

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

(5) Read parameter setting

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

function	function
GFS_SetGmode	Ejection method setting from CD buffer
GFS_SetTmode	Forwarding method setting
GFS_SetReadPara	Setting the read unit to the CD buffer
GFS_SetTransPara	Transfer unit setting from the CD buffer
GFS_SetTrFunc	Transfer function registration
GFS_StartTrans	Start transfer in transfer function

(6) Other

It provides CD pickup control, error handling function registration, and error status acquisition functions. The error handling function is called when an error occurs.

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

function	function
GFS_CdMovePickup	Moving the CD pickup
GFS_SetErrFunc	Registration of error handling function
GFS_GetErrStat	Getting error status
GFS_ConvTno	Track number conversion

1.3 Module configuration

Figure 1.1 shows the position of this library with respect to hardware and other software. The dotted line is the module included in the debug 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 that does not support position independent code for SH7600

• SEGA_CDC.LIB
  CD communication interface library

• SEGA_DMA.LIB
  DMA library

• SEGA_CSH.LIB
  Cache library