Re: the least EPICS_CA_MAX_ARRAY used for EIGER2 4M detector

[Mark Rivers via Tech-talk <tech-talk at aps.anl.gov>]

Hi Zhibang,

What to you mean when you say ADViewer? Do you means the ImageJ plugin EPICS_AD_Viewer.java, which uses Channel Access? If so then I strongly suggest that you switch to EPICS_NTNDA_Viewer.java.  That uses pvAccess and 2 big advantages:

- It does not use EPICS_CA_MAX_ARRAY_BYTES.

- It can read compressed data. With ADEiger the detector sends compressed data to the driver. You can send that compressed data directly to NDPluginPva, which sends it to ImageJ. The compression factors are usually much greater than 10x. You can also send the compressed data directly to 

the HDF5 plugin. You need to send the compressed data to NDPluginCodec to decompress it for other plugins like statistics and ROI plugins that don’t understand compressed data.

Mark

Sent from my iPhone

On Feb 27, 2026, at 3:16 AM, Zhibang Shen via Tech-talk <tech-talk at aps.anl.gov> wrote:



Hi,

I am facing a problem with EPICS_CA_MAX_ARRAY_BYTES while using ADViewer monitoring Eiger2 4M detector.

I have followed the installation instruction of ADEiger and it works well. But if I set EPICS_CA_MAX_ARRAY_BYTES=10,000,000, ADViewer reports the exception of pendIO timed out. I also followed the troubleshooting to see whether all the configuration are properly set. The ArrayCallback PVs of cam1: and image1: are both set to Enable, and EPICS_CA_MAX_ARRAY is set to 40,000,000. I also tried EPICS_CA_MAX_ARRAY_BYTES=100,000,000 but it does not work either.

The pixel number of Eiger2 4M detector is 2068x2162=4,471,016. And the image bit depth is set to 32. I think the least EPICS_CA_MAX_ARRAY should be 2068x2162x4=17,884,064, then EPICS_CA_MAX_ARRAY_BYTES=40,000,000 should work. But it doesn't. I don't know why.

Could someone help me with this issue? Thanks in advance for any help.

Best regards,

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Zhibang Shen

Institute of High Energy Physics, Chinese Academy of Sciences

19B Yuquan Road, Shijingshan District, Beijing, China

100049