Avago Technologies LSI53C1010 - Manual (Page 190)

8-4 Writing Device Drivers with SCRIPTS
8.2 Command Block
When the operating system interface layer of the SCSI device driver
receives an I/O request, it creates a data structure in host memory. This
data structure contains the information required by the hardware
interface for that specific request. This information generally includes:
•
Length of the array
•
SCSI ID for the target device
•
Logical unit number (LUN)
•
Length of the command block
•
SCSI command containing the beginning block and the number of
blocks to be transferred
•
A place for the hardware interface to write its completion status. The
operating system interface reads the completion status and uses it
to update the scheduler information.
8.3 Power Up Example
The hardware interface initializes the chip whenever the system is
powered up or reset. In the DOS example in
Figure 8.3 , the system BIOS
scans host memory for a ROM, signified by a 55AA code. It reads the
third byte of the ROM, which contains a jump address. The following
SCRIPTS processor initialization information is located at that address:
•
diagnostics to be run
•
SCRIPTS to be loaded
•
data buffer areas to be reserved
After performing these tasks, the hardware interface scans for the hard
disk and after locating it, downloads the operating system. The operating
system cannot be loaded from the disk until the SCSI driver is active.
This power on sequence of activities is illustrated in
Figure 8.3 .