piLagTesterPRO and the raspberry pi4: an alpha release is available

The piLagTesterPRO is a tool to measure display input lag, using custom hardware plugged into a raspberry pi. It works great on the pi 0, a $5 computer that out-specs SGIs from the mid-90s. It also works great on higher end PIs, such as the Pi3, which has a much faster processor but the same GPU as the pi0. 

**** UPDATE: full Pi4 is now available, the text below is out of date *****

It's now available for the pi4 too! but first some background:

The raspberry pi4 has been a problem because it uses a new GPU with much better specs but no backwards compatibility. For a while I've been working on supporting it. While it kind of worked, it wasn't ready for prime time, but now the official firmware and my work-around for bugs in the firmware seem to have reached a threshold where it would be reasonable to make a testing release.

While it works well for me I don't have the equipment to test the higher resolutions and refresh rates that the PI4 offers. Since this is the reason for using the Pi4 in the first place, I'm hesitant to call this a beta. Instead it's an alpha. This is not out of undo caution (I think). The Pi4 firmware has a bug where moderately high demands on the CPU cause the GPU to drop frames and it's very difficult to detect this in software, AND still know what the right value is.  From an end user perspective it's easy to tell something's up though: input lag will suddenly change by 16ms. I think I've got the code optimized enough to avoid this issue but there is a chance it will occur for higher refresh rates or resolutions. 

That's why I need your help. I need folks to test this on a range of displays and see if the input lag values stay constant or start to jump up/down by exactly 16ms. So for those of you who already own the piLagTesterPro and have a pi4, please try this image on your pi4. if you have an earlier pi, there's no reason to try this image. 

here's the download link; please don't use unless you have a pi4 and a piLagTesterPRO as it will eventually use up my quotas:

 https://1drv.ms/f/s!Ahb4rgU6L_z9gxV287CTdwmz8mvh

currently requires a 16gb microsd card, write it as you would any raspbery pi OS image.

login as root, password = t (just the letter t). you will see instructions after you log in.





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