Browse Prior Art Database

Message Transport using Direct Memory Access Facilities

IP.com Disclosure Number: IPCOM000115324D
Original Publication Date: 1995-Apr-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 124K

Publishing Venue

IBM

Related People

Benning, CS: AUTHOR [+6]

Abstract

Described is a method by which a Direct Memory Access (DMA) data bus may implement message transport protocols. The method maps a segment of each bus unit's DMA address space to one or more message queues, in a manner that does not require synchronization dialogues common to shared memory schemes.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 46% of the total text.

Message Transport using Direct Memory Access Facilities

      Described is a method by which a Direct Memory Access (DMA)
data bus may implement message transport protocols.  The method maps
a segment of each bus unit's DMA address space to one or more message
queues, in a manner that does not require synchronization dialogues
common to shared memory schemes.

      Described is a method to implement message transport protocols
using the DMA facilities of a data bus.  This method is comprised of:
  1.  a message packet structure
  2.  recipient message queues
  3.  a process by which a sending bus unit transports message
packets
       to a recipient bus unit's Message Queue, using the DMA
facilities
       of the common data bus.

      The Figure illustrates the structural relationships of the
sending and receiving DMA bus units and the message packet and queue
elements.

Message Packet Structure - The method utilizes a message packet that
is a singular unit of data, of a length less than or equal to that
maximum quantity of data that may be transmitted in an atomic DMA
operation, between two bus units interconnected by the DMA bus.  The
message packet is further characterized as being transmitted to a
single, contiguous region within the storage of the DMA receiving
unit, and as having a single DMA status indication from the DMA
receiver associated with that storage region as a whole.

Message Queue Characteristics - The method utilizes one or more
recipient message queues, each of which receives message packets as
queue elements.  An instance of such a queue is characterized to a
message sending bus unit as:
  1.  having as its identity a single recipient storage address,
       conformant to the DMA architecture of the DMA bus.  This
       identity, or "address", is constant and independent of the
number
       of message packets held within the queue at any given time.
  2.  capable of receiving message packets of a length less than or
       equal to some maximum.  This maximum message packet length is
a
       characteristic of each particular message queue and may  be
less
       than that maximum message packet length associated with the
       underlying DMA bus architecture.
  3.  is associated with a set of empty message buffers, which are
not
       separately addressed by sending units as the target region of
a
       DMA operation.  These buffers receive message packet data
       transmitted via DMA to the storage region identifying the
message
       queue itself.

      A DMA bus unit that receives message packets communicates to
other, sending bus units these characteristics of each of its message
queues.  The method by which bus units communicate these
characteristics is dependent upon the specific DMA bus or other
interconnections that exist between sending and receiving bus unit,
and may be implicitly speci...