CD-ROM SCSI-2 COMMAND REFERENCE MANUAL VERSION 3.1 (OB-U0077C)
NOTES:
1)The CD-DA block lengths are totally irrelevant to the logical block length set by the Mode Select(6) command. This command would not change the block length field in the MODE SELECT command.
2)While the SCSI buffer is being filled, the drive is able to prepare with no overlap or missing data in response to the consecutive commands which read contiguous CD-DA blocks.
When the host cannot read the data quick enough and the buffer is full, the drive will stop refilling the buffer. The host is still capable of reading all CD-DA data in the SCSI buffer with consecutive read commands without overlap or missing bits at the block boundary. Once the buffer is full, the first read command to read the next sequential CD-DA block(e.g. X+1) after the last CD-DA block(e.g. X) in the buffer will cause a Check Condition with a sense key of 05h and an additional sense code of BAh(buffer overflow). There is no check condition for a read command which does not request block X+1(e.g. a Read(X+2, 1) command). In addition, a second read command which requests block X+1 will not get a check condition.
For Example (In case that the last CD-DA block stored in the buffer is X): In a Read(X-2, 5) command to read block X-2 to X+2, the drive returns three CD- DA data blocks and then a check condition. The drive returns the block X+1 address in the information bytes(byte 3 to 6) of a subsequent Request Sense command. There are no overlap of missing bits for blocks X-2, X-1 and X. Block X and X+1 are not transferred. That is; in case of reading CD-DA blocks, the drive has only rough access. Once the data stream from the media has been stopped, it is unable to have such pin-point access as in CD-ROM blocks. (Each CD-ROM block always includes the CD-ROM Header that provides the pin-point access.)
3)The volume level control is not performed on any SCSI CD-DA data. Analog audio output is not performed while SCSI CD-DA data is in transaction, either.
4)The drive transfers data to the host at the burst transfer rate for the entire block of data. The drive's firmware overhead should only occur at a block boundary. Upon completion of the read operation, the drive enters the Hold Track state during inactive time.