Pi4J 2.8.0 always reads GPIO inputs as LOW on Raspberry Pi Zero W (Bookworm, kernel 6.12, libgpiod 1.6.3) while gpioget works

[jandeclerck]

Title:
Pi4J 2.8.0 always reads GPIO inputs as LOW on Raspberry Pi Zero W (Bookworm, kernel 6.12, libgpiod 1.6.3) while gpioget works

---

Description:
On my Raspberry Pi Zero W running Raspberry Pi OS Bookworm (32-bit), kernel 6.12.47+rpt-rpi-v6, and libgpiod 1.6.3, Pi4J 2.8.0 always reads all GPIO input pins as LOW, regardless of their actual hardware state.
Other tools (gpioget, raspi-gpio, pinctrl) report the correct state.

---

Environment:

• Board: Raspberry Pi Zero W (code: 9000c1)
• OS:
  PRETTY_NAME="Raspberry Pi OS Bookworm"
  NAME="Raspberry Pi OS"
  VERSION_ID="12"
  VERSION="12 (bookworm)"
  ID=raspbian
  ID_LIKE=debian
• Kernel:
  Linux 24sPiZero 6.12.47+rpt-rpi-v6 66666 #1 SMP PREEMPT Debian 1:6.12.47-1+rpt1 (2024-08-01) armv6l GNU/Linux
• Java:
  openjdk version "17.0.16" 2023-07-18
  OpenJDK Runtime Environment (build 17.0.16+8-Raspbian-1deb12u1rpi1rpt1)
  OpenJDK Client VM (build 17.0.16+8-Raspbian-1deb12u1rpi1rpt1, mixed mode)
• libgpiod:
  gpiod version 1.6.3
• Pi4J: 2.8.0
• pigpiod: Not running (systemctl status pigpiod shows inactive)

---

Steps to Reproduce:

1. Connect jumpers or set GPIO pins to HIGH/LOW using hardware or external pull resistors.

2. Confirm correct pin state using:

   • gpioget gpiochip0 <pin>
   • raspi-gpio get <pin>
   • pinctrl

3. Run the following minimal Pi4J test program:

   package org.janssen.twentyfour;
   
   import com.pi4j.Pi4J;
   import com.pi4j.context.Context;
   import com.pi4j.io.gpio.digital.*;
   
   public class GpioInputTest {
       public static void main(String[] args) throws Exception {
           Context pi4j = Pi4J.newAutoContext();
   
           int[] pins = {4, 7, 8, 11, 17, 18, 23, 24, 27};
           String[] names = {
               "reset14Btn (GPIO4)",
               "jump2 (GPIO7)",
               "jump1 (GPIO8)",
               "start60Btn (GPIO11)",
               "reset24Btn (GPIO17)",
               "show24Btn (GPIO18)",
               "pls1SecondBtn (GPIO23)",
               "mns1SecondBtn (GPIO24)",
               "timerBtn (GPIO27)"
           };
   
           for (int i = 0; i < pins.length; i++) {
               DigitalInput input = pi4j.create(DigitalInput.newConfigBuilder(pi4j)
                   .id("gpio" + pins[i])
                   .name(names[i])
                   .address(pins[i])
                   .pull(PullResistance.OFF)
                   .build());
               System.out.printf("%-20s : %s%n", names[i], input.state());
           }
   
           pi4j.shutdown();
       }
   }

4. Run with:

   sudo java -cp /home/pi/twentyfour/classes:/home/pi/twentyfour/lib/* org.janssen.twentyfour.GpioInputTest
   

---

Expected Result:
Pi4J should report the actual state of each GPIO input (HIGH or LOW), matching the result from gpioget and raspi-gpio.

Actual Result:
All GPIO inputs are always reported as LOW by Pi4J, regardless of their actual state.
gpioget and raspi-gpio report the correct state.

---

Additional Information:

• No other GPIO daemons (e.g., pigpiod) are running.
• The issue persists with both hardware and software pull resistors.
• This issue blocks GPIO-based configuration and input detection on Pi Zero W.

---

Thank you for your help!

[eitch]

From what i know, i think you need PULL_DOWN. Can you try that?

[jandeclerck]

I tested that previously(.pull(PullResistance.PULL_DOWN)), it didn't work either. I have hardware pulldown resistors in my hardware.

[FDelporte]

@jandeclerck can you please check if you have similar results with a previous version like 2.7.0?
I guess you can't upgrade to a newer version with Java 21 as you are running on a Pi Zero?

[jandeclerck]

@FDelporte Thank you for your help.
I have tried it but same issue. I tried 2.0 2.5 2.7 and 2.8

[FDelporte]

In that case, I suspect something is wrong with the wiring or overall setup...
Are you using the BCM numbers?
https://api.pi4j.com/board-information/ZERO_W

Another idea: can you try this example https://github.com/Pi4J/pi4j-example-minimal with a V2?

I can try this later myself with a Pi Zero, but not this week...

[jandeclerck]

There is no urgency here, I know you are busy this week.

I am using BCM numbers.
I compiled this minimal example with java 17, since java 21 is not compatible with RPI Zero.
But some dependencies are compiled in java 21 and it will not run:
pi@24sPiZero:~/pi4j-example-minimal/distribution $ java -cp "pi4j-example-minimal-0.0.1.jar:./*" com.pi4j.example.MinimalExample Exception in thread "main" java.lang.UnsupportedClassVersionError: com/pi4j/util/Console has been compiled by a more recent version of the Java Runtime (class file version 65.0), this version of the Java Runtime only recognizes class file versions up to 61.0 at java.base/java.lang.ClassLoader.defineClass1(Native Method) at java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1017) at java.base/java.security.SecureClassLoader.defineClass(SecureClassLoader.java:150) at java.base/jdk.internal.loader.BuiltinClassLoader.defineClass(BuiltinClassLoader.java:862) at java.base/jdk.internal.loader.BuiltinClassLoader.findClassOnClassPathOrNull(BuiltinClassLoader.java:760) at java.base/jdk.internal.loader.BuiltinClassLoader.loadClassOrNull(BuiltinClassLoader.java:681) at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:639) at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188) at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:525) at com.pi4j.example.MinimalExample.main(MinimalExample.java:60)