IPL File
The IPL file specifies information so that the CDROM BIOS can locate and run the initial program on the data track of the disc, and is located right at the beginning of the track. It consists of a 2048 byte sector with development credits for the CDROM2 system that gets checked against the same data present on the System Cards for licensee authentication, and another sector with user configuration, laid out as follows:
| Offset | Label | Size (bytes) | Description |
|---|---|---|---|
| 0 | IPLBLK | 3 | Sector address of your game's data |
| 3 | IPLBLN | 1 | # of sectors to load from disc. |
| 4 | IPLSTA | 2 | Destination address for loaded data |
| 6 | IPLJMP | 2 | Address to start executing code from after loading is complete |
| 8 | IPLMPR | 5 | MPR configuration for user area banks (MPR 2 to 6) |
| 13 | OPENMODE | 1 | Bitflags for enabling auto load and display of VRAM/ADPCM data on boot |
| 14 | GFXBLK | 3 | OPENMODE bg graphics sector address |
| 17 | GFXBLN | 1 | OPENMODE bg graphics sector length |
| 18 | GFXADR | 2 | OPENMODE bg graphics VRAM address |
| 20 | ADPBLK | 3 | OPENMODE ADPCM data sector address |
| 23 | ADPBLN | 1 | OPENMODE ADPCM data sector length |
| 24 | ADPRATE | 1 | OPENMODE ADPCM data sampling rate |
| 25 | (reserved) | 7 | “reserved” zeroed out bytes |
| 32 | (id string) | 74 | “PC Engine CD-ROM SYSTEM”, 0, “Copyright HUDSON SOFT / NEC Home Electronics,Ltd.”, 0 |
| 106 | (prog name) | 16 | User defined field for game identification |
| 122 | (dev name?) | 6 | Extension of the progname field or developer id |
The remaining data on this sector must be zero-filled. IPLMPR values range from 0 to 7, since they refer to the IFU-30 RAM exclusively (hardware mapped to banks $80-87), meaning that even in a Super CDROM^2 able BIOS, which has RAM mapped into the cartridge ROM space ($68-7f), you're limited to 64 kilobytes in the initial disc load.
Opening Mode
The OPENMODE byte serves as bitflags for defining whether or not you want to load initial data into VRAM/ADPCM RAM and if you want to display/play them.
| Bit | Description |
|---|---|
| 7 | Load from GFXBLK (disc) to GFXADR (VRAM)? |
| 6 | Load from ADPBLK (disc) to $0000 (ADPCM RAM)? |
| 5~3 | Unused |
| 2 | Turn off video display? |
| 1 | Turn off ADPCM playback? |
| 0 | Play ADPCM sample once (0) or on repeat (1)? |
The data in GFXBLK for the preset background spans four sectors, one for the background palette, one for the BAT data, and two sectors for the tileset of the background.
