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Fibre Channel Interface Manual, Rev. D 337
12.64.1 Combined Header and Data mode (000b)
In this mode, data to be written to the disc drive’s data buffer is preceded by a four-byte header.
The Byte Transfer Length includes a four-byte header and the Write Buffer data. A transfer length of zero indi-
cates that no data transfer takes place. This condition does not create the Check Condition status. If the trans-
fer length is greater than the Buffer Capacity reported by the Read Buffer header, the disc drive creates the
Check Condition status with the sense key of Illegal Request. In this case no data is transferred from the initia-
tor.
It is not considered an error to request a transfer length less than the Buffer Capacity.
Buffer ID and Buffer Offset fields are all zero.
The write data following the Write Buffer CDB consists of a four-byte Write Buffer header (which always pre-
cedes the data) plus the data to be written to the data buffer as follows:
12.64.2 Write Data Only mode (010b)
The byte transfer length specifies the maximum number of bytes that are transferred and stored in the drive
buffer. No header bytes are included. The Buffer ID and Buffer Offset fields are all zero.
12.64.3 Download Microcode and Save mode (101b)
In this mode, vendor-unique executable microcode (which is not preceded by a four-byte header) is transferred
to the control memory space of the target and, if the download is completed successfully, will also be saved.
The downloaded code is then effective after each power cycle and reset until it is replaced using another down-
load microcode and save operation. When the download microcode and save command has been completed
successfully, the target generates a Unit Attention condition for all initiators with an extended sense of Power
On, Reset, or Bus Device Reset Occurred (Sense Data Error Code 29 03h). Following the downloading of new
microcode, the drive may need to be reformatted before it can perform properly.
For this mode (101b) the command bytes of Table 227 are interpreted as shown below:
Buffer ID and Buffer Offset fields (CDB bytes 2–5):
These bytes are all zero.
Byte Transfer Length (CDB bytes 6, 7 and 8):
The transfer length (in bytes) of the downloadable code. This value must be the exact length of the download
data. A value of one signifies one byte of download data, etc.
Control Bytes (CDB byte 9):
All bits zero.
Table 229: Write Buffer header
Bit
Byte
76543210
000000000
100000000
200000000
300000000
4 - n
Data to be written into disc drive buffer