如何使基于tslib的校准永久保留？

Question

I'm having problem making a permanent calibration in my embedded solution. I'm developing a Qt-based app for a Embedded Linux environment with touch screen. For this last part, I use tslib (configured by previous developers).

In what comes to simply calibrate the touch screen, everything is fine: ts_calibrate runs and creates the pointercal file correctly. If after calling ts_calibrate I run my Qt app (or ts_test), I can notice that the calibration is successful.

The problem is that the calibration results only works for 1 opening of my app: I calibrate with ts_calibrate, run my app, close it and if I run my app again, the screen is one again non-calibrated.

Now obviously I don't want to have to call the calibration each time my app is closed and reopened. The question is: how to make the calibration results become permanent? (that is, till another calibration is made)

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Extra info:

I did some research on the web and I found this SO thread telling about a way to handle this problem using QWSServer . At first I disliked this solution since it depends on the Qt framework to do the job (I was expecting a more general, "C++ solution" (or a call to a script, whatever)). But I implemented it and it worked - but only in a specific case, namely, if I calibrate, open my software, close it and reopen it, then the calibration is maintained. But the problem nevertheless persists if I shut down the hardware completely, turn it on and run my app without a call to ts_calibrate (reloading the Linux kernel in the process); so this show to be only a partial solution and, therefore, not acceptable.

Trying to find the source of the problem, I created a copy of the pointercal file just after calibration and another copy of it after shutting down and turning up my hardware (and confirming that the calibration was over) and I noticed that the file was changed in the middle despite no call to the ts_calibrate or similar app was made:

After calibration: 55438 118 -1920736 -543 -36058 34531168 65536 800 480

After hardware shutdown: -55040 1280 2526720 -288 35040 -34398240 -62768

The terminal log for the linux boot ( tftp; bootm command) don't mention pointercal or a relevant calibration process.

Edit

I recently learned that the pointercal file located inside /etc/ is changing between sections because that entire folder is made new when the hardware is restarted. So what is essentially happening is that Tslib is going after a file that is constantly reset to default each time the hardware is restarted, and what I need to do is to configure Tslib not to look there, but to a more secure folder (in my case, the SD Card). The new question now is: how to do that? I know I have to configure the tslib.sh file making the TSLIB_CALIBFILE variable point to the new location of pointerscal , but tslib.sh is itself inside /etc/ , being itself temporary.

Answer 1

You have to change TSLIB_CALIBFILE in the image loaded via tftp.

That should do it, since you just have to change that once.