Browse Prior Art Database

Printer Using Direct Memory Access to Reduce Communications Bandwidth

IP.com Disclosure Number: IPCOM000119402D
Original Publication Date: 1991-Jan-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 71K

Publishing Venue

IBM

Related People

Jordan, DD: AUTHOR [+6]

Abstract

Disclosed is a system for reducing the processor bandwidth required to accept inbound data communications. This system uses a combination of Direct Memory Access (DMA), custom hardware and control software.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 53% of the total text.

Printer Using Direct Memory Access to Reduce Communications BandWidth

      Disclosed is a system for reducing the processor
bandwidth required to accept inbound data communications.  This
system uses a combination of Direct Memory Access (DMA), custom
hardware and control software.

      Many printers handle the processing of inbound data via
dedicated interrupt service routines.  Each time a new inbound byte
is received, the interrupt routine is executed. The data is moved
from an I/O port into a data buffer. Significant processor bandwidth
is required to perform this task.

      This article describes a system that employs DMA, custom
hardware and control software to perform inbound data communications
at greatly reduced processor bandwidth requirements.  A block diagram
containing a high-level schematic of the data communications design
is given in the figure.

      Parallel data communications are performed as follows:
      1.   The host sends an input data byte to the printer.
           Printer hardware places the byte in the parallel
           communications port, asserts a BUSY signal to the
           host, and asserts a DMA request to the printer
           processor.
      2.   The printer DMA hardware places a copy of the
           input data into the input buffer.  Parsing of the
           input buffer is performed in the usual manner.
      3.   As soon as the DMA hardware reads the
           communications port, the printer hardware negates
           the BUSY signal.
      4.   The input buffer parser is responsible for moving
           data out of the input buffer.  Depending on the
           size of the buffer, the speed of the parser, and
           the inbound data rate, it may be possible to fill
           the buffer.  If the parser sees that the buffer is
           becoming full, the parser will instruct the
           printer hardware to assert a BUSY si...