DLP4500: Is 120Hz Video mode supported?

Dear Alex,

thanks a lot for the quick and detailed reply - this is very helpful! I will test this and come back to you here.

best

Tobias

Hi Alex,

I finally found some time to test your settings. Bottom line: I am afraid, it did not work for us.

EDIT: we use an Nvidia RTX3070TI (latest drivers) on Windows 10.

This is what I did:

Using an EDID editor (CRU -  https://www.monitortests.com/forum/Thread-Custom-Resolution-Utility-CRU) I exactly copied your EDID settings from above (here 1280x800)

The DLP4500 control software reports exactly your values:

However, whereas 120Hz is shown, the effective refresh rate is not 120Hz and far below the refresh rate at the standard 60Hz setting. I hope this is evident from the following movie:



This is me wiggling a mouse pointer - if I do the same at the standard 60Hz at 1280x800 it looks like this



60Hz  DLP4500 control software report:

I have updated to the latest firmware version 4.4.0 

Did you compare your displayed video content between the nominal 120Hz and the standard 60Hz? The moving dots on your video look a bit \choppy' as well.

In any case, this is the same situation as I had before (and similar to several other posts before me - see above): reported 120Hz with clearly dropped / not displayed frames.


Best wishes

Tobias

Hello Tobias,

The choppiness of the dots may just be because I was videoing with my phone but it is not choppy. Please give our team some time to check between 120 Hz and 60 Hz performance and we will get back to you next week.  

Regards,

Alex Chan

Hello Tobias,

I compared betwen 60 hz and 120 hz and do not see any issues with either when we are using a video generator with moving patterns.

Regards,

Alex Chan 

Here is a screenshot of a single frame of your movie. Assuming the dots have a smooth motion and you are recording at 30 fps with your phone (if the metadata is to be believed), you would expect the dots to be either a smear (long exposure), or to be at a single position. The fact that sometimes the dot seem to be duplicated is to me a strong indication that the display may be running at 30fps/2, i.e. 15 fps, which is what most of us experience with this device !
If the dots were not moving smoothly (that is jumping forward in each frame by a lot) but still updated at 120 fps, I would expect to see more than two copies in each stillframe, which I am not seeing. Am I getting something wrong ?

Best regards,

Martin Privat

Hello Martin,

Thanks for your reponse, please give our team some time to look into this further next week. 

Thanks,

Alex Chan

Hello Tobias, my understanding is that the HDMI receiver chip (TFP401) supports up to 165MHz pixel clock (which corresponds to HDMI v1.0, so any HDMI cable should also work) which is higher than the 150MHz supported by the DMD controller chip (DLPC350) on the lightcrafter 4500, so likely not a bottleneck;
Best,
Martin Privat

Hello Alex and Tobias,

In my experience, the 15Hz issue always manifests itself with a 'Forced Swap' error on the GUI.
Funnily enough, I think this is illustrated in the Lightcrafter EVM manual (dlpu011f)

The manual also mentions:
'''
This error can occur if the DLP LightCrafter 4500 is set to
Video Mode and the vertical backporch timing is too small.
'''

I don't have a lightcrafter handy to test right now, but that may be a direction worth investigating

Best,
Martin Privat

Hi Martin,

thanks a lot! Indeed (as you see in the screenshot above) we have a forced swap issue... Will play with backporch settings and report here.

Interestingly, we also have a "buffer freeze" at 120Hz - but not at 60Hz (which, however, also has a "forced swap" error).

It also seems to me that the many 120Hz issues reported here over the last 10 years occur with NVIDIA cards... (very soft information, of course).
But for reference: We use a RTX3070TI. 

It would be great to hear from a user if they got it running in a similar configuration. 

Best
Tobias

Hello Everyone,

I was looking into the firmware for version 4.4 and did not see any sequence timings for 120 Hz but the team is looking into this further. I have also replicated the forced swap and buffer freeze issue at 120 Hz in our GUI as well and the team is looking into this further. 

Regards,

Alex Chan

Hello Everyone,

I discussed internally and another engineer confirmed 120 Hz should work and pointed me to the following E2E posts. I am working with that engineer to do some further testing. 

https://e2e.ti.com/support/dlp-products-group/dlp/f/dlp-proucts-forum/614841/dlp4500-need-help-getting-120hz-refresh-rate-with-dlp4500-evm

https://e2e.ti.com/support/dlp-products-group/dlp/f/dlp-products-forum/729572/linux-dlplcr4500evm-dlp4500-works-at-115-hz-but-not-120-hz

Regards,

Alex Chan

Hi,

Thanks a lot !

I tried the EDID in the suggested link https://e2e.ti.com/support/dlp-products-group/dlp/f/dlp-products-forum/729572/linux-dlplcr4500evm-dlp4500-works-at-115-hz-but-not-120-hz

and it does not work for me (I have an image but it is still choppy @ around 15fps).

I think the best way to check if the display is running properly at 120Hz is to use a video with a clock or counter updated at 120Hz, and image with a 120Hz camera (potentially triggering the camera with the projector). I have included such a video that was generated with the following python script.

```

import cv2
import numpy as np

duration_sec = 5
fps = 120
sz = (1140, 912)
color = True
num_frames = duration_sec * fps

writer = cv2.VideoWriter(f'clock_{fps}Hz.avi', cv2.VideoWriter_fourcc(*'MJPG'), fps, sz, color)

org = (sz[0]//4, sz[1]//2)
font = cv2.FONT_HERSHEY_SIMPLEX
fontScale = 10
mod = fps//15
colors = np.vstack((
    np.linspace(0,255,mod, dtype=np.uint8),
    np.zeros((8,), dtype=np.uint8),
    np.linspace(255,0,mod, dtype=np.uint8)
))
thickness = 15
anti_aliasing = cv2.LINE_AA

for i in range(num_frames):
     col = (int(colors[0,i%mod]), int(colors[1,i%mod]), int(colors[2,i%mod]))
     frame = np.zeros((sz[1],sz[0],3), dtype=np.uint8)
     frame = cv2.putText(frame, str(i), org, font, fontScale, col, thickness, anti_aliasing) 
     writer.write(frame)

writer.release()
```




If you don't have a 120Hz color camera handy, the color of the counter is updated with frame number modulo 8, meaning that the color will remain constant if the frame rate is 15Hz, which you can see by eye.

The following videos are taken at 120Hz with a grayscale camera.
Here is what I get with the Lighcrafter 4500 configured for 60Hz:

If you look image by image, you can see that the counter is updated by 2 every two frames. This is expected

Here is what I get with the Lighcrafter 4500 configured for 120Hz:

If you look image by image, you can see that the counter is updated by around 8 every 8 frames, with a significant jitter. This is not normal

To be clear, when the DLP4500 is set to 120Hz, everything looks fine superficially. You can measure VSYNC and it clocks at 120Hz, the same probably holds true for output triggers. It's just that the image projected is not updated. Since there is a Forced Swap error, it looks to me like the DLP is not properly loading frames into the internal display buffer, or not properly cycling between the two images in the internal display buffer (as if it was cycling back to the same image for 7 or 8 cycles).
So if you don't look closely at what is projected, it can be easy to miss.
After 7 or 8 frames however the next image is loaded (all images in between have not been displayed), giving an effective frame rate of around 15Hz.

Hope this helps,
Best,
Martin Privat

Hello Martin,

Thank you for the information.

Regards,

Alex Chan

Hi Martin,

thanks a lot for this much more precise quantification of the issue. This is _exactly_ our problem.

Alex: Our application is very time-critical - getting 120Hz video to run would be important. I much appreciate you looking into it!

Best
Tobias 

 

Hello Alex

Thanks a lot,

Please do let us know if you have more info on this.
In the meantime you may want to update the documentation for the DLPC350

For readers interested in the topic, do note that 8-bit grayscale in Pattern mode works at 120Hz as described in the documentation with the timings provided here: https://e2e.ti.com/support/dlp-products-group/dlp/f/dlp-products-forum/729572/linux-dlplcr4500evm-dlp4500-works-at-115-hz-but-not-120-hz. While one can chose which combination of LEDs are used, it does not allow to project more than one color for each frame to the best of my knowledge.

Thanks again,
Best regards,

Martin Privat

Hello Alex,

Would TI be willing to open source the firmware on the DLPC350?
I understand very well that a lot of time and effort went into designing the firmware,
and it would probably not make sense for TI to do that, but one can dream :D

It would be a very valuable tool for the community though
Thanks again for your help,

Best Regards,

Martin Privat

Hi Alex,

this is indeed quite unfortunate. 120Hz was one of the reasons we considered this device. Can you say if any refresh rate above 60Hz video is supported? 

I will see if we can achieve something with a Pattern Sequence over HDMI.

Best wishes
Tobias

Hello Martin and Tobias,

Unfortunately, we don't share source code except the firmware we released on the product page. 

Please allow us some time to check if we have any firmware build that can support above 60Hz.

Regards,

Lori 

Thanks a lot!

Hello Tobias,

At this time it appears we only have sequence database support for 60 Hz. I am looking into higher frame rate support but am not sure what higher frame rate sequence databases are available or if new ones will have to be developed which could take time and resources. 

Regards,

Alex Chan

thanks - will try.

Understood. 

Regards,

Alex Chan