Browse Prior Art Database

Automatic Rate Pacing for a Serial Port

IP.com Disclosure Number: IPCOM000113909D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 101K

Publishing Venue

IBM

Related People

Williams, DD: AUTHOR

Abstract

Disclosed is the modification of serial port hardware to provide burst data transmission at the maximum rates supported by the hardware, as long as the receiving station is actively ready to process incoming data. When processing delays occur, data transmission is suspended until processing time is again available. In a first implementation, the Data Terminal Ready (DTR) and Buffer Full lines of the receiving station are interlocked. In a second implementation, a retrigerable single shot is used to control transmission rates.

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This is the abbreviated version, containing approximately 52% of the total text.

Automatic Rate Pacing for a Serial Port

      Disclosed is the modification of serial port hardware to
provide burst data transmission at the maximum rates supported by the
hardware, as long as the receiving station is actively ready to
process incoming data.  When processing delays occur, data
transmission is suspended until processing time is again available.
In a first implementation, the Data Terminal Ready (DTR) and Buffer
Full lines of the receiving station are interlocked.  In a second
implementation, a retrigerable single shot is used to control
transmission rates.

      Normally, serial data transmission rates are limited to a rate
that is compatible with the worst case processing capability of the
receiving system.  This rate can be significantly less than the
actual overall rate that could be obtained.  Available bandwidth is
effected by many factors, including higher level interrupts, system
functions, such as battery power management, and data buffer
management, such as writing the received data to a storage device.

      A number of methods exist for improving serial data
transmission rates to levels above this limitation of compatibility
with worst case processing capability.  These current solutions
include software pacing, hardware pacing, and packets.

      In some cases, transmission rates can be improved through
software pacing.  With this method, if the receiving software
determines it needs additional time, it sends an XOFF command telling
the transmitting program to suspend sending data until a
corresponding XON command is received.  This method works well as
long as the processing environment is well known.  When this is the
only method used, high transmission rates are difficult to achieve,
and interactions with other system functions still fail.

      Existing hardware pacing methods are similar to the software
pacing method.  The receiving program still needs to know when more
time is needed in order to change the state of the receiving hardware
for automatically controlling the transmitting station.  One method
for doing this involves turning off the DTR line of the receiving
system.  If this DTR line is connected to the Clear To Send (CTS)
line of the sending system, the transmitting hardware then suspends
transmission.  This method still encounters problems when data rates
are increased and when interaction occurs with other system
functions.

      Another software method for increasing data rates is the
transmission of data in relatively small packets at a rate which is
higher than the rate which can be sustained over...