Experimental Physics and
Industrial Control System

Folsk,

 

I am trying to read a large array from a VME IOC using caget.  The array is 500000 elements, 32-bit integers.  EPICS_CA_MAX_ARRAY_BYTES is set to 2000000 on the IOC, which is “just large enough” to read the entire array.  EPICS_CA_MAX_ARRAY_BYTES is set to 20000000 (10 times larger than large enough) on the Linux client.

 

The IOC is running 3.14.12.1.

 

Here is the output of caget from a Linux client with EPICS 3.14.10, 3.14.11, and 3.14.12.1 when requesting 499000 elements, (1000 fewer than maximum) which should fit in EPICS_CA_MAX_ARRAY_BYTES.

 

3.14.10:

corvette:mca/iocBoot/iocVxWorks>date ; /usr/local/epics/base-3.14.10/bin/linux-x86/caget -#499000 -w20 SIS:3820:mca1 > temp.out ; date

Tue Jun  7 17:03:37 CDT 2011

Tue Jun  7 17:03:38 CDT 2011

 

3.14.11:

corvette:mca/iocBoot/iocVxWorks>date ; /usr/local/epics/base-3.14.11/bin/linux-x86/caget -#499000 -w20 SIS:3820:mca1 > temp.out ; date

Tue Jun  7 17:03:55 CDT 2011

Tue Jun  7 17:03:56 CDT 2011

 

3.14.12.1:

corvette:mca/iocBoot/iocVxWorks>date ; /usr/local/epics/base-3.14.12.1/bin/linux-x86/caget -#499000 -w20 SIS:3820:mca1 > temp.out ; date

Tue Jun  7 17:04:07 CDT 2011

CA.Client.Exception...............................................

    Warning: "The requested data transfer is greater than available memory or EPICS_CA_MAX_ARRAY_BYTES"

    Context: "op=0, channel=SIS:3820:mca1, type=DBR_TIME_LONG, count=500000, ctx="server unable to load read (or subscription update) response into protocol buffer PV="SIS:3820:mca1" max bytes=2000024""

    Source File: ../getCopy.cpp line 92

    Current Time: Tue Jun 07 2011 17:04:07.629564143

..................................................................

 

 

So on 3.14.10 and 3.14.11 it works as expected, caget is requesting fewer than the number of bytes that EPICS_CA_MAX_ARRAY_BYTES will allow, and it succeeds.  But it fails on 3.14.12.1.  The error message says count=500000.  Is it trying to read all 500000 rather than the number requested?

 

The same error happens on 3.14.12.1 even if I try to only read 100 elements:

 

corvette:mca/iocBoot/iocVxWorks>/usr/local/epics/base-3.14.12.1/bin/linux-x86/caget -#100 -w20 SIS:3820:mca1

CA.Client.Exception...............................................

    Warning: "The requested data transfer is greater than available memory or EPICS_CA_MAX_ARRAY_BYTES"

    Context: "op=0, channel=SIS:3820:mca1, type=DBR_TIME_LONG, count=500000, ctx="server unable to load read (or subscription update) response into protocol buffer PV="SIS:3820:mca1" max bytes=2000024""

    Source File: ../getCopy.cpp line 92

    Current Time: Tue Jun 07 2011 17:24:56.617989921

..................................................................

 

 

 

I then increased EPICS_CA_MAX_ARRAY_BYTES on the IOC to 2000200, i.e. 200 more than the theoretical minimum number.  I then did a caget of the entire array, and it worked fine on all 3 versions of EPICS base.

 

corvette:mca/iocBoot/iocVxWorks>date ; /usr/local/epics/base-3.14.10/bin/linux-x86/caget -w20 SIS:3820:mca1 > temp.out ; date

Tue Jun  7 17:16:25 CDT 2011

Tue Jun  7 17:16:26 CDT 2011

corvette:mca/iocBoot/iocVxWorks>date ; /usr/local/epics/base-3.14.11/bin/linux-x86/caget -w20 SIS:3820:mca1 > temp.out ; date

Tue Jun  7 17:16:44 CDT 2011

Tue Jun  7 17:16:45 CDT 2011

corvette:mca/iocBoot/iocVxWorks>date ; /usr/local/epics/base-3.14.12.1/bin/linux-x86/caget -w20 SIS:3820:mca1 > temp.out ; date

Tue Jun  7 17:16:55 CDT 2011

Tue Jun  7 17:16:56 CDT 2011

 

 

So it looks like there is something wrong with 3.14.12.1 when EPICS_CA_MAX_ARRAY_BYTES is not large enough for the entire array, even when many fewer elements are being requested.

 

Mark