ASIGetExpStatus 250+ ms delay on Linux

wulfblat

I have been working on the indi ASI driver and have noticed there appears to be a fixed 250+ millisecond delay from when the exposure should be finished and when ASIGetExpStatus reports that it has completed.

I added timers to the ASI SDK demo program main_SDK2_snap and found the same delay there.

The delay seems to be a minimum of 270ms even with small 8 bit image sizes (256x256) and the bandwidth set to 80%. The exposure time does not appear to affect the delay, although if I set the image size small (for example, 32x32) the delay grows to over 1 second (for a 1 ms exposure).

I see this with an ASI174mini on a USB2 bus and an ASI294mc on a USB3 bus. The system is idle and there is no other USB activity when running the test.

Is there a reason for such a long delay? Is there some setting I can use to reduce it?

yang

There is setting up procedure before and after actual exposure, it will take excess time.

nightfly

This is really a disappointment. One the benefits of having fast readout and low readout noise in CMOS cameras is to allow for short exposure times. With large apertures and short exposures you can do lucky imaging and get much sharper images for DSOs without fast guiding. Isn't there any way to reduce such a huge setup time (in the firmware or in the driver), without resorting to (8-bit) video mode?

Thanks!

- Emmanuel.

Sam@ZWO

only video mode don't have such delay

smroid

ASI120mm mini user here. I also see the 250+ ms delay between starting an exposure and having ASIGetExpStatus report success even when the exposure time is much shorter than this.

In video mode, I'm observing the same 250+ ms delay to the first call to ASIGetVideoData returning; subsequent calls to ASIGetVideoData do return at the frame rate interval (50ms in my test). So I can verify Sam@ZWO's statement that video mode can avoid the 250+ ms delays.

However, during active video capture, I experiment with changing camera settings. If I call ASISetROIFormat, I incur a 250+ ms delay for the next ASIGetVideoData call; thereafter it goes back to my 50ms interval. On the other hand, I can call ASISetStartPos without disturbing the ASIGetVideoData intervals.

It would be great if I could change the ROI between video frames just like I can change the startpos between video frames. More generally, eliminating the 250ms delays would be terrific. Even reducing the 250ms as much as feasible would be helpful.

Thanks,
-Steven

Software@ZWO

smroid
Hi Steven,
You mentioned that when you first called ASIGetVideoData, the Delay was 250+ms. I think this may be because after calling ASIStartVideoCapture, the camera needs to do some necessary initialization processing. When making ROI, you need to first call ASIStopVideoCapture to stop camera exposure, then set ROI, and then call ASIStartVideoCapture to start camera exposure. Therefore, when you first call ASIGetVideoData, the Delay is 250+ms.

Best Regards