GE 90-70 manual Finding the Memory Available for Application Program Storage

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Finding the Memory Available for Application Program Storage

Shared I/O data is stored in the same memory as application program storage. To find the amount of memory available for application program(s), subtract the overall transfer data amount from the amount of memory (512K bytes for CGR772, 1024K bytes for CGR935) available for the application program.

First, calculate the amounts of input and output data transferred:

Reference Type	Reference Size	If Point Faults are Disabled:		If Point Faults are Enabled:
%I	Bit	(%I length x 4 ) ÷	8	(%I length x 5) ÷	8
%AI	Word	(%AI length x 2)		(%AI length x 3)
%Q	Bit	(%Q length x 4) ÷	8	(%Q length x 5) ÷	8
%M	Bit	(%M length x 4) ÷	8
%AQ	Word	(%AQ length x 2)		(%AQ length x 3)
%R	Word	(%R length x 2)

Then, add the input amount, the output amount, and an additional 8K bytes for synchronization information:

total bytes of input data (%I, %AI) transferred

+total bytes of output data (%Q, %AQ, %M, %R) transferred

+8 Kbytes for synchronization information

Last, subtract this amount from the total amount available for the application.

For example, if there are 10 Kbytes of input data transferred and 20 Kbytes of output data transferred, then 10 Kbytes + 20 Kbytes + 8 Kbytes = 38 Kbytes needed for transferred data. This is subtracted from the 1024 Kbytes of total memory on the CGR935:

1024K - 38K = 986 Kbytes available for the application program on the CGR935.

System Communications Window Considerations

The CGR772 and CGR935 model CPUs support the use of high-speed communications modules such as the Ethernet Interface (Type 2). Requests from devices attached to these communications modules are handled in the System Communications Window. Since these requests can be sent in large volumes, there is the potential for the Systems Communications Window to be processing requests for a significant amount of time. One way to reduce the risk of timing out the Redundancy Communications Module/Bus Transmitter Module communications link between the CPUs is to configure the System Communications Window for LIMITED WINDOW mode. This sets a maximum time for the Systems Communications Window to run. Other options are to configure the CPU sweep mode as CONSTANT WINDOW or CONSTANT SWEEP. The CPU will then cycle through the communications and background windows for approximately the same amount of time in both units.

3-4 Series 90™-70 Enhanced Hot Standby CPU Redundancy User's Guide – May 2000 GFK-1527A