[Classroom Development] Displayio locks SPI bus

[demc]

CircuitPython version

7.3.3

Code/REPL

import board
import time
import terminalio
import displayio
import busio
from adafruit_display_text import label
from adafruit_st7789 import ST7789
from xpt2046 import Touch
from digitalio import DigitalInOut, Direction

# Release any resources currently in use for the displays
displayio.release_displays()

TFT_WIDTH = 320
TFT_HEIGHT = 240

tft_dc = board.GP8
tft_cs = board.GP9
spi_clk = board.GP10
spi_mosi = board.GP11
spi_miso = board.GP12 # added this
tft_rst = board.GP15 # changed this
backlight = board.GP13
spi = busio.SPI(spi_clk, spi_mosi, spi_miso)

display_bus = displayio.FourWire(spi, command=tft_dc, chip_select=tft_cs, reset=tft_rst)

display = ST7789(
    display_bus,
    width=320,
    height=240,
    rotation=90,
    backlight_pin=backlight
)

touch_cs = board.GP16

touch_x_min = 164
touch_x_max = 1826
touch_y_min = 164
touch_y_max = 1928

touch = Touch(spi, cs=touch_cs,
              width=320, height=240,
              x_min=touch_x_min, x_max=touch_x_max,
              y_min=touch_y_min, y_max=touch_y_max)


group = displayio.Group()
display.show(group)

Behavior

displayio.FourWire locks the SPI bus. The xpt2046 driver can not talk to the board because they share the same SPI bus.

Description

I am educator working on curricula using Pico + CircuitPython.

I've purchased a class set of waveshare lcd screens: https://www.waveshare.com/wiki/Pico-ResTouch-LCD-2.8#Arduino

I am by no means an expert but after reading #1760 it appears that there are limitations with the existing implementing of FourWire that effectively cripples this hat.

Here's what I've observed:

1. The ST7789 is able to work fine in isolation. I can render things on the screen.
2. The xpt2046 is able to work fine in isolation. I can read touch events reliably from the screen.
3. Combining displayio with xpt2046 doesn't work because I can not use the LCD and Touch chip select pins as laid out in the wiring of the waveshare device.

Looking closely at the waveshare docs, I've gathered that both the ST7789 and xpt2046 are sharing the same SPI bus. I can toggle either device by setting GP9 (LCD_CS) or GP16 (touch CS). As best as I can tell, toggling those pins configures which device is transmitting information on the SPI bus (correct me if I'm wrong or naive).

Trying to manually toggle GP9 to momentarily disable the LCD screen so I can read from the touch screen does not appear to work because I get an error about the pin being in use (I get why this restriction exists, but it's really weird).

I am open to any suggestions! If I can't figure out how to make this work, I will have to rewrite my curricula for MicroPython because of the restrictions imposed by CircuitPython.

As an aside:

It was mentioned in #1760 that I could probably use the RGB display driver instead of displayio. I'm not sure if that is suitable because I need to be able to render text, which, as far as I can tell, is only possible using displayio.

Thank you!

Additional information

No response

[Neradoc]

You don't need to toggle the pins manually, the drivers do that on their own. What is that xpt2046 module your are importing ?
Note: This looks like a support issue, they are better handled on the forums or the Adafruit discord.

[deshipu]

The drivers should handle the CS pins internally, you don't need to toggle them yourself. It should just work. The #1760 is really about sharing the D/C and reset pins between two or more displays.

[demc]

Thanks for the quick reply!

I am using an adaptation of this MicroPython driver. Waveshare did not publish their own native driver.

Thank you for pointing me to Discord. I will also try asking this there.

Pertaining to hats that use a single SPI bus for both the display and other peripherals, is that actually supported by displayio?

Are there any additional resources I can read about this?

[demc]

@Neradoc very kindly helped me figure this out on Discord. Closing.

I will publish the combined driver when I get all the peripherals working perfectly.