I'm thinking: 1) that the LVGL Gregory linked to is a contender for the graphical interface, only for LVGL of course, to do the calibration 2) The existing calibration routines in nuttx-apps (e.g. ccalibration for NXWM as suggested by Alan C. Assis) is a great alternative for non-LVGL implementations 3) Developers can write their own front end if preferred.
All produce the necessary offsets and scale factors etc. In my case, the screen is only used by pudgy, often gloved, fingers so absolute accuracy is not required; any variations between displays are not an issue as there are large touch button areas that are difficult to miss! That just leaves the question of where/how to calculate compensated x/y co-ordinates that take the offsets into account. I see there is CONFIG_TSCALIBRATION used by platform_setconfig, currently only used by mikroe boards that I can see, along with some structs (i.e. sCalibrationData) but there is no "generic" TSD driver in nuttx/drivers. Perhaps that is something that one day might be a useful enhancement, as it could then standardise the struct(s) etc. and provide "methods" along the lines of efuse, power/supply, and so on. Ultimately, the offsets/scaling do need to be applied somewhere though, and to me, IOCTL to the ADC driver feels right. In the case of the SAMA5 a read via the character driver is what actually initiates a TSD sample, so the overhead of calculating offsets seems acceptable, but other processors/implementations could do this on a timer etc so it's not a definitive approach. I will implement IOCTLs, using the sCalibrationData struct as the argument and see how I get on. >From: Gregory Nutt <spudan...@gmail.com> >Sent: Tuesday, May 23, 2023 7:51 PM > > >On 5/23/2023 12:11 PM, Tim Hardisty wrote: >> Hi, >> >> >> A touchscreen peripheral (SAMA5D2 as it happens) delivers X and Y >coordinates scaled 0-4095. >> >> LVGL wants them scaled to the actual size of the display (800x480 in my >case). >> >> 2) Enhance the chip's TSD driver after all, using a Kconfig setting to >enable X/Y scaling to the display's size (set in board-specific files >already). >> > >Many touchscreens require calibration by the application via a >calibration screen. Hence, only the application knows the scale factors >to use and so scaling is done by the application. > >Scaling could also be done by the driver using calibration information >provided via an IOCTL. All resistive touchscreens require calibration. >If your touchscreen does not require calibration, then I suppose it could >even be provided by a configuration setting. > >Raw, unscaled input is also needed by the application, however (in order >to do calibration, for one). > >Scaling in the driver could also be inefficient since the driver does not >know if the sample will be used or not. It might be better to to scale >in the application even if calibration is not necessary. > >A quick Google provides some references for touchscreen calibration with >LVGL: > > * https://forum.lvgl.io/t/calibrate-a-touchscreen-with-tpcal-h/244 > * https://github.com/jakpaul/lvgl_touch_calibration > >The are other calibration displays under nutts-apps/ (not for LVGL)
