Browse Prior Art Database

Method to Control Video Streams to be Passed to Modern Multitasking/Multiuser Operating Systems

IP.com Disclosure Number: IPCOM000118063D
Original Publication Date: 1996-Aug-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 87K

Publishing Venue

IBM

Related People

Flurry, G: AUTHOR [+3]

Abstract

Disclosed is a method to deliver video streams to modern operating systems that support virtual memory with non-contiguous physical memory. This method builds upon a method of connecting video streams to slow busses described in (*) by adding the capability of recognizing the physical page boundaries in a video stream and using a new physical address for each page.

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

Method to Control Video Streams to be Passed to Modern Multitasking/Multiuser
Operating Systems

      Disclosed is a method to deliver video streams to modern
operating systems that support virtual memory with non-contiguous
physical memory.  This method builds upon a method of connecting
video streams to slow busses described in (*) by adding the
capability of recognizing the physical page boundaries in a video
stream and using a new physical address for each page.

A simple block diagram of the system is shown below:

                            (Image Omitted)

      Today's modern multitasking/multiuser operating systems provide
memory buffers to users in demand-paged virtual memory.  These
virtual buffers appear continuous to the user of the buffer, but in
fact, the memory management functions of the operating system and, in
general, the  CPU complex, actually implement these virtual buffers
in non-contiguous  pages in physical memory.  All current video bus
interface chips that perform Direct Memory Access (DMA) as a bus
master for the PCI bus assume  that the physical memory for a video
buffer is contiguous; this is possible since older operating systems
and graphics cards have contiguous  physical memory buffers.  The
disclosed method allows a bus interface chip designed to DMA to
contiguous physical memory to work with an operating system that
supports only non-contiguous physical memory.

      The bus interface chip used in the specific implementation of
the disclosed method is the Philips SAA7145, which corresponds to the
Bus Interface block in the Figure.  This chip loads the physical
address, from a specific control register, that is the target of the
DMA operation  at each vertical synchronization pulse it receives;
the intent is to start each new video field at a new physical
address.  The 7145 also has  a Register Programming Sequencer (RPS)
that allows detection of the various video signals and external
events, and allows loading of the 7145 control registers.  The
disclosed method for causing the 7145 to DMA to non-contiguous
physical memory consists...