New DmTftLibrary

Original code modifications

First step was to correctly assign pins to the Nucleo board. Pin mapping between the Nucleo WB55 board and the TFT28-105 shield is as follows:

DM-TFT28-105	P-NUCLEO-STM32WB55	Arduino name	Description
TFT_CS	PA4	D10	TFT Chip Select
TFT_D/C	PA9	D9	TFT Data/Command
T_CS	PC6	D2	Touch Chip select
T_IRQ	PA10	D3	Touch PENIRQ
SD_CS	PC10	D4	SD Card select
F_CS	PA15	D5	Flash Memory CS
SCLK	PA5	D13	SPI Clock
MISO	PA6	D12	SPI MISO
MOSI	PA7	D11	SPI MOSI

Interface with TFTF28-105 parts is based on SPI solely. We have to deal with very different frequencies for each controllers:

Part	IC	Clock freq. (max.)
TFT	ILI9341	14 MHz
Touch	XPT2046	2.5 MHz
Flash Memory	W25Q32BV	50 MHz

The original has been ported from C++ to C. Not that I dislike C++, but it is totally useless here and generates too much code.

Moreover, I found that communication with the TFT module was too slow and these parts have been rewritten (approximately a factor of 10 has been achieved). The culprit was an unnecessary repeated sequence of CS - 2 byte transfer - /CS operations that slowed down things a lot. Using SPI capabilities and intermediate buffer use for repeated values made things a lot faster.

The touch part has also been almost entirely rewritten. First, the documentation on the XPT2046 is inaccurate and misleading. Code was also misleading in the correct interpretation of the PENIRQ output from the chip. A resistive touch interface mainly consists in ADC conversion after applying voltage either on Y axis or the X to measure the position in X or Y respectively. Conversion is triggered by CS signal and setting voltage drivers on and off approprietally. This was not properly done and a lot of code to compensate “weird” values and final X,Y position was trying to fix things. This has been completely cleaned up.

As mentioned above, SPI speed is changed when addressing a module or another. Due to a choice of 32MHz for Core-0, the SPI clock prescaler allows 8, 2 and 32MHz for TFT, Touch and Flash memory module respectively.