Can't read correct values from a rpi B 1

[jvalrog]

I'm using pin 4 (gpio 4) with this simple code:

require "pi_piper"

pin = PiPiper::Pin.new(:pin => 4, :direction => :in)

loop do
        puts pin.value
        sleep 0.1
end

I use a jumper and connect it to gpio4 and 3.3V (top-left).

It always shows a 0. If I change the jumper to GND (bottom-left), I also get a 0.

Reading the values from /sys/..., it shows correctly a 1 or 0, but the pi_piper script will always show a 0.

What's wrong? (I'm using pi_piper 2.0)

See the attached screenshot

[elmatou]

just update the value in memory with pin.read.
I'm not a huge fan of this implementation, but we don't want to change it for compatibility sake.

[jvalrog]

mmm I see now, it's cached.

Do you think something may break if you alias valueand read???

Who needs it to be cached? Why would you want to read an "old" cached value that may be incorrect?

[elmatou]

Yep, value is used against last_value to 'detect' changes.
If this behavior really annoy you, you could monkey patch PiPiper::Pin with

    def value
      @value = read
    end

[jvalrog]

Ah, now I understand why they chose this implementation. It's a bit inconsistent, as you said, because it's not clear what method should be used for getting an updated value without looking into the source code.

I think I have a solution to "fix" (let's call it that way) this inconsistency:

def changed?
    @changed
end

def value
    val = Platform.driver.pin_read(@pin)
    @changed = (@last_value != val)
    @last_value = val
    invert ? (val ^ 1) : val
end

alias_method :read, :value

I think nothing breaks with that change, and the alias is there for backward compatibility. @value is not used anymore. changed? remains constant betweens reads, as the original code.

Just my 2 cents.

[zsyed91]

While I agree that it may be a bit inconsistent. We have this method already read.

This is the new code via the rewrite for 3.0:
https://github.com/jwhitehorn/pi_piper/blob/develop/lib/pi_piper/pin.rb#L97.

And this is the original implementation currently in release:
https://github.com/jwhitehorn/pi_piper/blob/master/lib/pi_piper/pin.rb#L150

We can certainly update the docs to make this more evident.

require "pi_piper"

pin = PiPiper::Pin.new(:pin => 4, :direction => :in)

loop do
        puts pin.read  # <--- this should work
        sleep 0.1
end