Implement new FFM API approach

[DigitalSmile]

Goal: create a plugin, that can talk to hardware using FFM API. It was introduced in JDK22 and is going to replace old JNI in future releases of JDK. For now it is marked for restricted use since next JDK25.

Todo list:

• Write some code, that works with FFM API objects (layouts, arenas, function calls, etc.)
• Implement all basic Provider interfaces (gpio, i2c, spi, pwm)
• Write JMH tests to measure performance
• Cover methods with tests and javadocs

[AlexR1973]

@DigitalSmile Please add implementation of 1Wire support also.

p.s. Is it possible for you to add support of 1Wire in your gpio library?

[DigitalSmile]

@DigitalSmile Please add implementation of 1Wire support also.
p.s. Is it possible for you to add support of 1Wire in your gpio library?

I didn't really work with 1-wire devices. Isn't it the protocol that can work above simple GPIO Pin?
Guess it is more high level application protocol so I don't know if it is good idea to add it into pi4j. Maybe @FDelporte can step in to this discussion?

[FDelporte]

About 1Wire support: there is work in progress by @dariuszzbyrad
See #435

[eitch]

Additionally the FFM-API approach isn't required, as one can directly read the kernel's relevant sys files. E.g. reading a temperature device:

String devicePath = "/sys/bus/w1/devices/28-0316a2791cff/w1_slave";
        try (BufferedReader br = new BufferedReader(new FileReader(devicePath))) {
            String line1 = br.readLine();  // e.g. "00 00 00 00 00 ... : crc=00 YES"
            String line2 = br.readLine();  // e.g. "00 00 00 00 00 t=12345"

            // Typically you look for "t=NNNNN" to get the temperature
            // Here, parse the integer after "t="
            String tempStr = line2.split("t=")[1];
            double tempC = Double.parseDouble(tempStr) / 1000.0;
            System.out.println("Temperature: " + tempC + "°C");
        } catch (IOException e) {
            e.printStackTrace();
        }

This is what @dariuszzbyrad has implemented.

[FDelporte]

Thanks @eitch , I added this info to a new web page: https://www.pi4j.com/documentation/io-examples/1-wire/

[AlexR1973]

Hello guys!
I know "/sys/bus/w1/devices/28-XXXX/w1_slave" location and currently read data from it in my project. But this data provided by OS driver. As far as I know there is another way to read data from the bus directly. Don't ask me how - I have a very basic knowledge about all these protocols and hardware implementations.
Disadvantage of reading data from /sys/bus/w1/devices/28-XXXX/w1_slave location, that it refreshed every 4-10 seconds (depends on the OS settings and implementation). If you need a more accurate value - read it directly from the bus.
p.s. If you interested my project is a home brewing system controller. I have 2 DS18B20, 3 relays for solenoid valves and a BPM180 pressure monitor to adjust temperature according to outside pressure. In a test environment on Java 17, Raspberry Pi ver2 rev B it can work for hours - no issues at all. But Orane Pi zero 3 is a completely different story - PITA in any step :(
Friend of mine asked me to do the same system for him and gave me his Orange Pi. I didn't know that 2 systems have such different guts inside them.

[FDelporte]

home brewing system controller

That calls for a new page in https://www.pi4j.com/featured-projects/! ;-)

[eitch]

@AlexR1973 from what i can see, there is no other way to read 1-wire devices in the kernel. At least nothing that i can find. if it takes 4-10 seconds, then perhaps its an implementation detail? Do you have any example code?

[AlexR1973]

@eitch , I have found the next article about working with DS18B20 over 1-wire interface. Please take a look at it - maybe it reveals the details how to get data directly. It is in Russian, but Chrome/MS Edge will translate it to English easily.

https://micro-pi.ru/%d0%bf%d0%be%d0%b4%d0%ba%d0%bb%d1%8e%d1%87%d0%b5%d0%bd%d0%b8%d0%b5-ds18b20-%d0%ba-orange-pi-bpi-rpi/

[AlexR1973]

@eitch ,

if it takes 4-10 seconds
4 seconds update time is not a showstopper in my case, even 10 secs is acceptable. But better to have the data when you need it, not when OS decides to update it for you.