Four. file access

4.1 Access model

Figure 4.1 shows a model diagram of file access.

Figure 4.1 Access function model

Transferring data from the CD-ROM to the CD buffer is called "reading," and transferring data from the CD buffer to the host area is called "extracting."
By using GFS_Fread and GFS_NwFread, applications can transfer data from CD-ROM without being aware of the read process.
Use GFS_NwCdRead if you want to control the reading process as well in your application.

4.2 Access pointer

The access pointer is updated by reading, so it moves sector by sector.
Figure 4.2 shows the movement of the access pointer when the following formula is executed to read 5000 bytes into the host area buf. After execution, the access pointer has moved from AP1 to AP2.

GFS_Fread(gfs, 3, buf, 5000);

Figure 4.2 Moving the access pointer

Table 4.1 shows the sector size for each file type.

Table 4.1 Sector length for each file type

file category	Sector length (byte)
CD-ROM Mode1	2048
CD-ROM Mode2 Form1 only	2048
CD-ROM Mode2 Form2 only	2324
CD-ROM Mode2 mixed	Indeterminate
DOS file	2048
memory file	2048

Reading is performed in sectors, while retrieval is performed in 4-byte units.

4.3 Parameters managed per file

The application can change five of the parameters managed by the library for each file opened. Those parameters are shown in Table 4.2.

Table 4.2 Parameters for each file

parameters	explanation	function to change	initial value
access pointer	start loading Off on the file to Set (unit: sector)	GFS_Seek	0
Eject mode	After removing the CD Buffer sector data Delete or leave Specify where to store	GFS_SetGmode	GFS_GMODE_ERASE
Transfer mode	Execute the retrieval process. Specify the device to use	GFS_SetTmode	GFS_TMODE_CPU
Load parameters	1 load Transfer by processing Maximum number of sectors	GFS_SetReadPara	GFS_RPARA_DFL
Retrieval parameters	1 time retrieval Transferred by processing number of sectors	GFS_SetTransPara	1

An open file occupies one CD block resource, one aperture and one buffer partition.