Motorola MVME166, Installation Manual

Page: 61 / 122

Disk I/O Support
MVME166IG/D2 3-15
3
When observing output from any 166Bug command, the XON and XOFF
characters which are in effect for the terminal port may be entered to control
the output, if the XON/XOFF protocol is enabled (default). These characters
are initialized to ^S and ^Q respectively by 166Bug, but you may change them
with the PF command. In the initialized (default) mode, operation is as
follows:
Disk I/O Support
166Bug can initiate disk input/output by communicating with intelligent disk
controller modules over the VMEbus. Disk support facilities built into 166Bug
consist of command-level disk operations, disk I/O system calls (only via one
of the TRAP #15 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
166Bug. 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 166Bug 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. 166Bug 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.
^S (wait) Console output is halted.
^Q (resume) Console output is resumed.