display: Interrupt driven ADC sampling for the touch screen #3
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* The code is built with -Werror and newer gccs warn on implicit fallthrough with -Wall -Wextra, so the build failed.
* The build failed with linker errors with gcc 8.3 (the inline functions could not be linked against). * The inline annotation were removed accordingly from functions that are linked, while those that are only used within one compilation unit were marked static inline instead.
* make -B did not work, because ln -s failed on existing links – fixed by using -f.
* Make the main loop non busy (use wfi instead). * Make the touch sampling interrupt driven. * Note: When starting with BURST_SWMODE there seem to be no ADC ready interrupts, so we use HWSCANMODE although we only want to sample once and disable the ADC in the interrupt handler. * Open question: Is there a point in not just sampling the touch screen in the main loop every 50ms and have the main loop wfi and be awoken by the systick interrupt (the ADC is pretty quick, 11 clocks of the ADC clock, which is 4MHz, so just 132 CPU clocks, and less than even a signle bit over the UART at 115200 baud). It may well be that the interrupt driven method burns more cycles while only marginally improving responsiveness (if at all).
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Wait for interrupt in the main loop and make the ADC-sampling of the touch screen interrupt driven.
This could probably still be improved (e.g. by moving all the post processing to events to the interrupt handlers.
It is not entirely clear whether doing the touch sampling with interrupts is worth it – the ADC is quite fast (about 130 CPU clocks / 2.7µs for a conversion) and while a conversion is in process the communication interrupts will still work. So waiting for the three required conversions in the main loop every 50ms may be the better solution (this takes less time than transferring a single byte over the UART at 115200 baud). – So perhaps these changes should be abandoned, but the main-loop should definitely wait for interrupts (it would be awoken at least every millisecond by the systick interrupt).
This includes #2.