Browse Prior Art Database

Strobe Time Adjusted Speedometer

IP.com Disclosure Number: IPCOM000112855D
Original Publication Date: 1994-Jun-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 77K

Publishing Venue

IBM

Related People

Chung, VE: AUTHOR

Abstract

Disclosed is a mechanism that optimizes the System Bus Chip data transfer from System Bus to System memory by changing threshold values to accommodate different system adapter's bus transfer speed.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Strobe Time Adjusted Speedometer

      Disclosed is a mechanism that optimizes the System Bus Chip
data transfer from System Bus to System memory by changing threshold
values to accommodate different system adapter's bus transfer speed.

      The System Bus I/O chip serves as an interface between the
system bus and the system memory.  This chip buffers data from the
system bus and then transfer the data into system memory.  A Strobe
time adjusted Speedometer is an apparatus used on a System Bus I/O
Chip to determine to optimal time to start moving data from the
buffer into system memory in an overlapping fashion such that data is
still being written into the buffer by the system bus.  This optimal
time is dependent on the bus transfer speed and the transfer size
which the speedometer will calculate a threshold value.  Because this
threshold value is variable, the system bus chip can start data
transfer from buffer to system memory at the most optimal time for
each different adapter in the bus and for each different transfer
size.  Previous speedometer implementation only worked on a single
transfer size (such as the largest one) or the threshold value is fix
(assuming one type of adapter speed).

      Fig. 1 is a conceptual drawing of the threshold variation
circuitry of the speedometer.  The Basic idea is of two registers: X
and Y.  Y register is loaded with an arbitrary value ConstantY at the
start of a new bus operation by New Transfer signal.  X is also
loaded with ConstantX by New Transfer.  X is decremented every clock
cycle.  When the strobe signal pulses, Y is loaded with the
subtraction of Y and X.  X gets reloaded with the initial value
ConstantX.  The longer the strobes are apart the smaller the value of
X become and the slower Y will be decremented.  When Y is zero or
less, the comparator will pulse a signal to start moving data from
buffer to system memory.

      ConstantY and ConstantX can be changed depending of the amount
of data transfer.  This will allow the speedometer to work on all
transfer size to allow more overlap.  These constant can be feed to
the speedometer via a selector or PLA logic.

      ConstantY and ConstantX values were determined experimentally
using Lotus 123 and the following equation was used to model this
speedometer.

              Strobe speed

  Y - (X -    ------------)  * # of strobes

                 cyctime

    Constants      x=       11       y=       14

    Strobe speed   50ns     60ns     70ns     80ns     90ns    100ns

    ---------+--------------------...