Appendix A
APPENDIX A PIONEER CD-ROM DRIVES - AUDIO FUNCTIONS
The CD-ROM drives consist of two logical subsystems - a CD reader and a controller. The controller receives SCSI commands, and sends commands to the reader for execution as needed. This allows audio commands to be executed in the background. At times, the two subsystems may be operating independently.
In addition to the normal audio commands, the CD-ROM drives support the Pioneer Laser Disc Player control commands. These alphanumeric mnemonics may be sent to the drive using the vendor-unique command WRITE CDP (Character Device Player). The WRITE READ CDP command strings are passed through the controller directly to the reader. The controller checks the length and termination of the command string, and, if valid, returns a GOOD status. The controller will generate a Check Condition with a sense key of ILLEGAL REQUEST if the string is not valid. The controller then passes the command string to the reader for execution. To receive the results of the command string, the initiator must use the READ CDP command to get the status from the reader. The reader passes the result data through the controller. Invalid commands or execution errors will not cause SCSI errors, but will be reported by the READ CDP command.
Certain types of data, such as the disc TOC, are stored by the controller once they have been read from the disc. If a disc has been accessed, a READ TOC command will not require a disc access, which could include a disc change. Instead, the TOC data is transferred from controller memory.