Browse Prior Art Database

High Performance DMA

IP.com Disclosure Number: IPCOM000106425D
Original Publication Date: 1993-Nov-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 2 page(s) / 51K

Publishing Venue

IBM

Related People

Tago, K: AUTHOR

Abstract

Disclosed is a mechanism to transfer data to/from virtual address space from/to peripheral devices.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 59% of the total text.

High Performance DMA

      Disclosed is a mechanism to transfer data to/from virtual
address space from/to peripheral devices.

      Existing DMA mechanisms transfer data to/from physical memory
from/to peripheral devices.  Operating systems need to convert
virtual address to physical address of the target memory pages and to
set page lock bits to prevent the target pages from being paged out
(pin-down) before starting the DMA transfer.

Two problems are associated with the scheme.

1.  The overhead from the address conversion and pin-down by
    software.

2.  Peripheral devices can not start I/O by themselves.  They need to
    ask operating system for address conversion and pin-down before
    staring the I/O.

      The problems can be eliminated by implementing a DMA mechanism
which can transfer data to/from virtual space from/to peripheral
devices.  The DMA hardware converts virtual address to physical
address before starting data transfer.  The address conversion is
implemented by accessing the page mapping table which is placed on
the main memory.  However, there is a difficulty in converting
virtual address to physical address by the DMA hardware.  The
operating system may modify the page mapping table during the DMA
transfer and the modification may cause an erroneous address
conversion by the DMA hardware.  The invention provides a way to
resolve the problem with low cost.

      The access right to the system bus of a computer sys...