Experimental Physics and
Industrial Control System

"Wang Xiaoqiang" <[email protected]> · Thu, 21 Apr 2011 22:23:18 +0200

Hi,

It seems for DBF_STRING array there is certain overhead, 16 bytes, when reading from CA client. In your case, setting EPICS_CA_MAX_ARRAY_BYTES to 2621416 works. I verified with caget from epics base

[-bash SLSBASE=/work]$ export EPICS_CA_MAX_ARRAY_BYTES=2621415
[-bash SLSBASE=/work]$ /usr/local/epics/base/bin/SL5-x86/caget -d DBR_STRING swave
Read operation timed out: some PV data was not read.
swave
    *** CA error The requested data transfer is greater than available memory or EPICS_CA_MAX_ARRAY_BYTES

[-bash SLSBASE=/work]$ export EPICS_CA_MAX_ARRAY_BYTES=2621416
[-bash SLSBASE=/work]$ /usr/local/epics/base/bin/SL5-x86/caget -#10 -d DBR_STRING swave
swave
    Data type:      DBR_STRING (native: DBF_STRING)
    Element count:  10
    Value:

The reason behind should be answered by experts then.

Best,
Xiaoqiang

-----Original Message-----
From: Ritesh Sugandhi [mailto:[email protected]]
Sent: Thu 4/21/2011 5:25 PM
To: Wang Xiaoqiang
Cc: [email protected]
Subject: Handling of String Array in CaChannel library

Dear Sir,

thanks for sharing the code,  using your code I have mange to read and write
array a simple array.

I am able to successfully enhance the code to  read and write a double array
of size 64k ( 65535) elements. in this case I am using
EPICS_CA_MAX_ARRAY_BYTES configuration was 524280 ( i.e. 65535 * 8 bytes for
double). this works successfully

I have declared a string Array of 65535 elements and this time I have setted
EPICS_CA_MAX_ARRAY_BYTES to 2621400 (i.e. 40*65535 considering size of 40
bytes for string) at server and client side. running with this gives error

$ python2.6 ca-channel-v1.6-demo-waveform-string-64k.py
('total values are', 65535)
The requested data transfer is greater than available memory or
EPICS_CA_MAX_ARRAY_BYTES
$

but when I set EPICS_CA_MAX_ARRAY_BYTES to greater then 26214*20 at client
side.* I get the correct data at client side.

code is

from CaChannel import *
from random    import *
def main():
  try:
    channel = CaChannel('Py:string64k')
    channel.searchw()
    newval=[]
    for i in range(65535):
newval.append("ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-$#")
    channel.putw(newval)
    print('total values are',channel.element_count())
    print(channel.getw())
    del channel
  except CaChannelException, status:
    print ca.message(status)
main()

record is

 record(waveform, "Py:string64k")
{
    field(DESC, "string array")
    field(NELM, "65535")
    field(FTVL, "STRING")
}

-----------------------------------------------------------

On Wed, Apr 20, 2011 at 4:21 PM, Wang Xiaoqiang <[email protected]>wrote:

>
> Hi,
>
> Load this into your IOC:
> record(waveform, "cawave")
> {
>     field(DESC, "numeric array")
>     field(NELM, "20")
>     field(FTVL, "DOUBLE")
> }
>
> >>> import CaChannel
> >>> pv=CaChannel.CaChannel('cawave')
> >>> pv.searchw()
> >>> pv.getw()
> [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
> 0.0, 0.0, 0.0, 0.0, 0.0]
> >>> pv.putw(range(12))
> >>> pv.getw()
> [0.0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10.0, 11.0, 0.0, 0.0,
> 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
> >>>
>
> Xiaoqiang
>  ------------------------------
> *From:* [email protected] [mailto:
> [email protected]] *On Behalf Of *Ritesh Sugandhi
> *Sent:* Wednesday, April 20, 2011 3:48 PM
> *To:* [email protected]
> *Subject:* Handling of Array in CaChannel library
>
> Dear Sir,
>
> Could I get an example of how to handle sub array and waveforms records in
> CaChannel-v1.6 library code.
>
> Best regards,
>
> ritesh Sugandhi
>
>
>

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System