HP Integrity NonStop H-Series - Manual (Page 23)

Interfacing With the Open SCSI I/O Process (IOP)
Open SCSI for Fibre Channel Controller Integrator’s Manual for HP Integrity NonStop NS-Series Servers—
3 -7
The WRITEREAD Buffer Header Block
The WRITEREAD Buffer Header Block
The header block for the WRITEREAD buffer ( Figure 3-4 ) contains fields needed by
the IOP to determine whether the buffer contains a CCB for controlling the device, to
check for compatibility, and to find the relevant pieces of data in the buffer.
The fields of the header block contain this information:
hdr_begin
This 4-byte field contains a specific ASCII value that indicates to the IOP that the
buffer contains a CCB to control the SCSI device. This value must be set to PASS
in ASCII (that is, 0h50415353) so that you can find it easily when you investigate
problems.
hdr_size
This 2-byte field contains the size of the header block in bytes. This value must be
set to 20.
version
This 2-byte field contains a version number used by the IOP and clients to
coordinate changes to the header block structure. The value of this field is initially
set to 1, and it is incremented each time the header block structure changes.
These changes are restricted to using the spare fields or adding an additional field
in front of the hdr_end field. It is intended that existing fields will not be moved or
redefined.
buffer_status
This 2-byte field is set to a nonzero value if either:
Figure 3-4. WRITEREAD Buffer Header Block Structure
hdr_begin
("PASS")
hdr_size version buffer_status ccb_offset spare_1 spare_2 hdr_end
("THRU")
Header
Block
CCB Sense Buffer
(optional)
Data Buffer
(optional)
009 CDT .CDD