Debugger General Information
3-10
Installation Guide
3
Disk I/O Support
197Bug can initiate disk input/output by communicating with intelligent disk
controller modules over the VMEbus. Disk support facilities built into 197Bug
consist of command-level disk operations, disk I/O system calls (only via one
of the TRAP #496 instructions) for use by user programs, and defined data
structures for disk parameters.
Parameters such as the address where the module is mapped and the type and
number of devices attached to the controller module are kept in tables by
197Bug. Default values for these parameters are assigned at power-up and
cold-start reset, but may be altered as described in the section on default
parameters, later in this chapter.
Appendix B contains a list of the controllers presently supported, as well as a
list of the default configurations for each controller.
Blocks Versus Sectors
The logical block defines the unit of information for disk devices. A disk is
viewed by 197Bug as a storage area divided into logical blocks. By default, the
logical block size is set to 256 bytes for every block device in the system. The
block size can be changed on a per device basis with the
IOT
command.
The sector defines the unit of information for the media itself, as viewed by the
controller. The sector size varies for different controllers, and the value for a
specific device can be displayed and changed with the
IOT
command.
When a disk transfer is requested, the start and size of the transfer is specified
in blocks. 197Bug translates this into an equivalent sector specification, which
is then passed on to the controller to initiate the transfer. If the conversion from
blocks to sectors yields a fractional sector count, an error is returned and no
data is transferred.
Device Probe Function
A device probe with entry into the device descriptor table is done whenever a
specified device is accessed; i.e., when system calls .DSKRD, .DSKWR,
.DSKCFIG, .DSKFMT, and .DSKCTRL, and debugger commands
BH
,
BO
,
IOC
,
IOP
,
IOT
,
MAR
, and
MAW
are used.
The device probe mechanism utilizes the SCSI commands “Inquiry” and
“Mode Sense”. If the specified controller is non-SCSI, the probe simply returns
a status of “device present and unknown”. The device probe makes an entry
into the device descriptor table with the pertinent data. After an entry has been
Solution Systems Technologies Inc.
720-565-5995 | [email protected] | www.solusys.com
Solution Systems Technologies Inc.
720-565-5995 | [email protected] | www.solusys.com
