Browse Prior Art Database

Data Old Indicator

IP.com Disclosure Number: IPCOM000114243D
Original Publication Date: 1994-Nov-01
Included in the Prior Art Database: 2005-Mar-28
Document File: 2 page(s) / 56K

Publishing Venue

IBM

Related People

Chliwnyj, A: AUTHOR [+2]

Abstract

A method for determining the latency of data transferred between two asynchronous processes is disclosed. The method provides a mechanism to detect if data has not been updated in a given period, and this period is variable under microcode control.

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

Data Old Indicator

      A method for determining the latency of data transferred
between two asynchronous processes is disclosed.  The method provides
a mechanism to detect if data has not been updated in a given period,
and this period is variable under microcode control.

      In real time control systems, input data is measured by
analog/digital means and converted to values in binary form which may
be read by a microprocessor.  The processor then uses this data to
control the system operation.  A very common problem with input data
is unknown latency, or age, of the input data read by the processor.
If the processor uses "old" data, it induces phase error into the
control process transfer function.  So typically information about
the latency of data must be provided to the processor to avoid or
compensate for phase error.

      For the tape drive system described here, analog/digital
converters and logic processing circuits update new servo input
values to registers at a fixed period in normal operation.  These
registers may then be read by the DSP processor to compute the
desired actuator values.  However, in the event of a tape dropout or
circuit malfunction, the input values may not be updated for extended
periods.  Thus it is necessary to signal this condition to the
microprocessor to prevent the processor from using old data.

      The chosen implementation uses the existing microcode path
length as the latency timer, while providing an additional bit in the
input data register called "D...