lvgl_swipe — Display + Touch Test for Waveshare 1.69" LCD

A Zephyr/LVGL test application that draws a green "Swipe to test!" home screen on the Waveshare 1.69" Touch LCD Module and switches screens based on swipe gestures from the CST816S touch controller.

This project supports two boards:

• nRF5340 DK — original target, working
• nRF54LM20 DK — current target, working as of 2026-04-26

Build directories are kept separate per board (build_53dk/, build_54lm20/).

Hardware

Display

Waveshare 1.69" Touch LCD Module — 240×280, ST7789V controller, CST816S capacitive touch.

The Waveshare display board has two pin headers, H1 and H2:

• H1 routes signals through onboard level shifters (3.3V MCU side ↔ configurable display side voltage).
• H2 is direct (no level shifters) for cases where MCU and display run at the same voltage.

For both DKs below, jumpers are set so the display board's VDDIO and VDD_TP are sourced from the DK's 3.3V rail and signals on H1 are passed through at 3.3V both sides:

Jumper	Setting
J1	1.2 + 1.3 (Ext → display side)
J2	2.1 + 2.2
J3	3.1 + 3.2
J4	4.1 + 4.2
J1.1 ("Ext")	wired to a 3.3V VDD pin on the DK

H1.10 (VCC) is wired to a DK 3.3V VDD pin to power the MCU side of the level shifters.

nRF5340 DK pin connections

Pins on H1 of the display board → nRF5340 DK GPIOs:

H1 Pin	Module Pin	Function	nRF5340 Pin
H1.1	LCD_DC	Display D/C	P1.11
H1.2	LCD_CS	Display CS	P0.11
H1.3	LCD_CLK	SPI SCK	P0.06
H1.4	LCD_DIN	SPI MOSI	P0.25
H1.5	LCD_RST	Display Reset	P1.10
H1.6	TP_SCL	I2C SCL	P1.03
H1.7	TP_SDA	I2C SDA	P1.02
H1.8	TP_RST	Touch Reset	P0.20
H1.9	TP_IRQ	Touch IRQ	P1.01
H1.10	VCC	3.3V	VDD
H1.11	GND	GND	GND
H1.12	LCD_BL	Backlight	VDD (hardwired)

The 5340 has flexible peripheral pin routing — most peripherals can map to most GPIOs. Backlight is hardwired to VDD (always on at full brightness).

nRF54LM20 DK pin connections

The 54L family has strict peripheral-to-port routing rules that make the 5340 pin choices invalid. After porting:

H1 Pin	Module Pin	Function	nRF54LM20 Pin
H1.1	LCD_DC	Display D/C	P1.11
H1.2	LCD_CS	Display CS	P1.15
H1.3	LCD_CLK	SPI SCK	P1.13
H1.4	LCD_DIN	SPI MOSI	P1.14
H1.5	LCD_RST	Display Reset	P1.10
H1.6	TP_SCL	I2C SCL	P0.03
H1.7	TP_SDA	I2C SDA	P0.04
H1.8	TP_RST	Touch Reset	P1.05
H1.9	TP_IRQ	Touch IRQ	P1.04
H1.10	VCC	3.3V	VDD
H1.11	GND	GND	GND
H1.12	LCD_BL	Backlight	P0.07 (PWM)

Peripheral instances:

• Touch I2C → i2c30 (TWIM30, LP domain)
• Display SPI → spi21 (SPIM21, Peripheral domain)
• Backlight → pwm20 driving a pwm-leds node, controlled via Zephyr's LED API

nRF54L pin planning notes

These rules took a long debugging session to nail down. Documented here so future me doesn't have to relearn them:

• TWIM/SPIM/UARTE instance numbering reflects the power domain, and each domain has a dedicated GPIO port:
  • *30 (LP domain) → must use P0 pins
  • *20, *21, *22 (Peripheral domain) → must use P1 pins
  • *00 (MCU domain, includes QSPI/HSSPI) → must use P2 pins
• Trying to route, e.g., TWIM22 to a P0 pin or SPIM21 to a P2 pin will appear to initialize fine in Zephyr but won't actually drive the pins.
• The nRF54LM20 DK has many GPIOs pre-allocated by the board itself:
  • P0.05–P0.09: Button 3 (P0.05), UART0 TXD/RXD/RTS/CTS (P0.06–P0.09). Avoid for application use unless you also disconnect the debugger UART via the Board Configurator.
  • P1.08, P1.09, P1.26: Buttons 0/1/2
  • P1.16–P1.19: UART1 (TXD/RXD/RTS/CTS)
  • P1.20, P1.21: 32.768 kHz crystal (free via SB1/SB2 cut, SB3/SB4 short)
  • P1.22, P1.25, P1.27, P1.28, P1.31: LEDs 0–3
  • P2.00–P2.05: External flash (QSPI). All of P2 is essentially off-limits without disabling the onboard flash.
  • P2.06–P2.10: Trace
• NFC pins (P1.01 = NFC1, P1.02 = NFC2) are configured for the NFC antenna by default. To use them as GPIO/I2C/etc:
  1. Add &uicr { nfct-pins-as-gpios; }; to the overlay (this writes UICR so the chip clears NFCT->PADCONFIG at boot). Note: &nfct { status = "disabled"; }; alone is not sufficient — that only unbinds the Zephyr driver.
  2. On the DK, move 0Ω resistors from R33/R34 to R3/R4 to break the NFC antenna routing and connect the pins to the GPIO header.

For full DK pin map see the nRF54LM20 DK Hardware User Guide.

Building

# nRF5340 DK
west build --build-dir build_53dk -b nrf5340dk/nrf5340/cpuapp --pristine

# nRF54LM20 DK
west build --build-dir build_54lm20 -b nrf54lm20dk/nrf54lm20a/cpuapp --pristine --sysbuild

Then flash:

west flash --build-dir build_54lm20

Configuration

prj.conf

Notable settings for the 54LM20 build:

• CONFIG_PM_DEVICE and CONFIG_PM_DEVICE_RUNTIME are disabled. With runtime PM enabled on this SDK version, the ST7789V driver wasn't being woken at init time and the display stayed black. Reintroduce PM later once basic functionality is solid.
• CONFIG_LED=y and CONFIG_LED_PWM=y enable the LED API used to drive the PWM backlight.
• CONFIG_I2C_SHELL=y, CONFIG_GPIO_SHELL=y, CONFIG_DEVICE_SHELL=y provide the diagnostic shell commands used during bring-up (i2c scan i2c30, gpio set, device list).

Debugging tips

If the display is black or touch fails, the shell commands worth running in order:

device list

Confirms which devices initialized. Look for cst816s@15 (READY) — if it shows DISABLED, the I2C init failed.

i2c scan i2c30

A working I2C bus with the touch chip connected returns 15 in the address grid. Empty grid = I2C not reaching the chip.

gpio conf gpio@10a000 7 o
gpio set gpio@10a000 7 1

Manually drives the backlight pin high to verify the LED circuit independent of PWM.

CST816S driver debugging notes (legacy, from 5340 work)

When debugging the touch controller, these modifications to Zephyr's cst816s driver were useful:

Force debug-level logging:

//LOG_MODULE_REGISTER(cst816s, CONFIG_INPUT_LOG_LEVEL);
LOG_MODULE_REGISTER(cst816s, LOG_LEVEL_DBG);

Some CST816 variants report a different chip ID. If the driver fails with failed reading chip id but I2C scan finds the device, try changing:

//#define CST816S_CHIP_ID 0xB4
#define CST816S_CHIP_ID 0xB5

Add logging inside cst816s_process() to see touch coordinates and event types in real time:

if (pressed) {
    LOG_DBG("pressed event: %d, row: %d, col: %d", event, row, col);
    input_report_abs(dev, INPUT_ABS_X, col, false, K_FOREVER);
    input_report_abs(dev, INPUT_ABS_Y, row, false, K_FOREVER);
    input_report_key(dev, INPUT_BTN_TOUCH, 1, true, K_FOREVER);
} else {
    LOG_DBG("not pressed event: %d, row: %d, col: %d", event, row, col);
    input_report_key(dev, INPUT_BTN_TOUCH, 0, true, K_FOREVER);
}

These are not required for the 54LM20 build to work — the stock driver paired with the correct pin/instance configuration is sufficient.