st7735: persist=True not honored

Type of Raspberry Pi

RPi 3 B+ running Arch Linux Arm

Linux Kernel version

Linux alarmpi 4.19.25-2-ARCH #1 SMP PREEMPT Tue Feb 26 01:20:52 UTC 2019 armv7l GNU/Linux

Expected behavior

I have written a test program to learn how to use your libraries, test.py:

import time
import RPi.GPIO as GPIO
from luma.core.interface.serial import spi
from luma.core.render import canvas
from luma.lcd.device import st7735
from luma.lcd.aux import backlight
from PIL import ImageFont

serial = spi(port=0, device=0, gpio_DC=25, gpio_RST=27)
device = st7735(serial, width=128, height=128, h_offset=1, v_offset=2, bgr=True, persist=True)

gpio_LIGHT = 24
light = backlight(gpio=GPIO, gpio_LIGHT=gpio_LIGHT, active_low=False)

font = ImageFont.truetype("Roboto-Bold.ttf", 14)

light.enable(True)

# Box and text rendered in portrait mode
with canvas(device) as draw:
    draw.rectangle(device.bounding_box, outline="white", fill="black")
    draw.text((10, 50), "Hello World", fill="yellow", font=font)
    draw.text((10, 30), "Hello World", fill="white", font=font)

input()

light.enable(False)
time.sleep(2)

I expected that the graphics will remain on screen and backlight will turn off and stay off after python script concludes.

Actual behavior

I used persist=True in the device setup expecting that the image would stay on the screen, but it did not, the screen becomes blank white. I also tried adding a switch at the end to turn the backlight off expecting it to stay off, but again, backlight is ON and screen is white. Finally, I added a 2 second delay at the very end to be able to see if the backlight control was working. It was, but the screen turns white with the backlight ON after the script ends.

I think that the cleanup of the gpio pins, turning them to tri-state inputs, causes the active high backlight to activate due to a 3.3V pullup in the circuit on the HAT, and the RESET to appear to go low, which would reset the chip.

Am I using the persist option correctly? Anything else I should try?

Thanks -Ted

[Rippert]

I went ahead and updated everything in the list. It didn’t make a difference, which I thought would be the case looking at the commits between 1.1.0 and 1.1.1.

Thanks for pointing out the pip command. I’m just getting started in python, so it’s good to know.

[Rippert]

$ pip list --outdated
Package   Version Latest Type 
--------- ------- ------ -----
luma.lcd  1.1.0   1.1.1  wheel
luma.oled 3.1.0   3.1.1  wheel
pip       18.1    19.0.3 whee