Browse Prior Art Database

Addport

IP.com Disclosure Number: IPCOM000099466D
Original Publication Date: 1990-Jan-01
Included in the Prior Art Database: 2005-Mar-14
Document File: 2 page(s) / 93K

Publishing Venue

IBM

Related People

Krager, KI: AUTHOR [+2]

Abstract

The CMSPCNIO program demonstrates a simple technique for interfacing VM/PC CMS operating system to a native I/O device that is not currently supported by VM/PC system. The following example of an IBM Color Plotter (Model 7371 or 7372), connected to the serial port of a Serial/ Parallel Adapter, can be used by a VM/PC CMS application and illustrates the technique.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Addport

       The CMSPCNIO program demonstrates a simple technique for
interfacing VM/PC CMS operating system to a native I/O device that is
not currently supported by VM/PC system.  The following example of an
IBM Color Plotter (Model 7371 or 7372), connected to the serial port
of a Serial/ Parallel Adapter, can be used by a VM/PC CMS application
and illustrates the technique.

      The overall strategy of this example is to make the native I/O
device appear to the system as a virtual disk device.  This is done
by adding a block device driver (CMSPCNIO) to DOS's CONFIG.SYS file,
which causes a drive letter to be assigned to it at boot time.

      Once this drive letter is known, a VM/PC minidisk is configured
with this letter as the "Drive ID".  A VM/PC CMS application can then
access the native I/O device using standard CMS disk I/O operations.

      CMSPCNIO program handles all Read and Write requests for the
virtual disk and redirects them to the native I/O device when
appropriate.  The intention is to redirect only those requests which
are destined for the native I/O device. All other I/O requests are
directed to an in- storage virtual disk.  Therefore, the minidisk
simulated by CMSPCNIO program functions identically to a normal
minidisk (except when native I/O Read and Write requests are made).

      Unique keyword prefixes are used to distinguish native I/O Read
and Write requests from other CMS disk I/O requests.  The keywords
used should be selected so that they are never likely to appear at
the beginning of the data associated with any non-native I/O request.

      The definition of the native I/O Read and Write requests is
given below.

      A Write request is used to send data to the native I/O device.
To be distinguished from other CMS disk I/O requests, the Write
request must be written to the beginning of a CMS disk file block on
the virtual minidisk simulated by CMSPCNIO program.

      The data length field is a 16-bit binary value, with the
high-order byte first, followed by the low-order byte. This field
specifies the length of the data only and does not include the write
keyboard or the field itself.

      A Read request is used to send a command to and receive data
back from the native I/O device.  To be distinguished from other CMS
disk I/O requests, the Read request must be pre-written to the
beginning of a CMS disk file block o...