Fujitsu M2488 manual Buffer ID Description Capacity

TAPE UNIT SCSI COMMANDS M2488 PRODUCT GUIDE

Table 4-131. Supported Buffer ID Values for Vendor Unique and Write Data Modes

BUFFER ID	DESCRIPTION	CAPACITY
0	Read/Write Data Buffer	Specified in the Buffer Capacity field of the Read Buffer Descriptor
		obtained via the Read Buffer command.
1	Read/Write non-volatile RAM	Specified in the Buffer Capacity field of the Read Buffer Descriptor
		obtained via the Read Buffer command (512 bytes).

NOTES:

1.The read/write data buffer and NVRAM are wrap-around buffers. Therefore, the entire capacity specified by the Read Buffer Descriptor is available, regardless of the offset specified.

2.Prior to allowing WRITE BUFFER command processing to occur for the read/write data buffer, the controller performs required positioning or synchronization. Buffered write data is written to tape and buffered read data is discarded.

3.There is only one 512-byte NVRAM area available. This area may be accessed by any initiator. The NVRAM is not partitioned into “per initiator” areas.

4.When a write buffer operation is performed in vendor unique or write data modes, a two byte CRC is appended. This CRC is handled in two ways when performing a read buffer operation depending on the Read Buffer mode. A Read Buffer in vendor unique mode reads the number of bytes requested and does not perform any CRC checking. A Read Buffer operation in data mode reads the number of bytes requested and an additional two bytes of CRC and then veri- fies the CRC. The CRC is then stripped away and not sent to the initiator with the other Read Buffer data.

**NOTE **

When performing Write Buffer operations to the Data Buffer, the max- imum Transfer Length that can be written is the Buffer Capacity of the Data Buffer minus two. The two remaining bytes in the Data Buffer are needed to store the two byte CRC which is automatically appended to the data when it is stored in the buffer

Download Microcode Mode (100b) Description. In this mode, vendor-specific microcode is transferred to the control store memory of the target via the data buffer and then an automatic reset is performed causing the target to run from the new microcode. The downloaded microcode is not saved into non-volatile memory (i.e. flash memory), therefore; after a power-cycle, the target reverts to the previous version of microcode. After SCSI bus or Bus Device resets, the target con- tinues to run from the downloaded code.

In the download microcode mode, Buffer ID 0 is the only Buffer ID supported. If any other Buffer ID value is selected, the target returns CHECK CONDITION status and sets the sense key to ILLEGAL REQUEST with an additional sense code of INVALID FIELD IN CDB.

NOTES:

1.Since an automatic reset is performed upon completing the Write Buffer command in Down- load Microcode mode, the MICROCODE HAS BEEN CHANGED unit attention condition is replaced with the POWER ON/RESET unit attention condition.

2.The microcode image that is downloaded via the WRITE BUFFER command includes the con- troller and servo microcode. In the Download Microcode mode, only the controller microcode is copied to control store and activated. The downloaded servo microcode is not used and the previous servo code remains active. In order to change the servo code, a WRITE BUFFER command in Download Microcode and Save mode must be performed, followed by a power- cycle.

4-146 CG00000-011503 REV. A April 1997