Need a Perl Guru.

[CptKrf]

GURU = Anyone who knows more than me. i.e. almost everyone.

I am making good progress in learning Perl, but am stuck on an item that I can't seem to find in the Mastering Perl books. (Or more likely, don't recognize.)

I am doing I/O projects on a PI 4, using the GPIO for all kinds of stuff. The access for the pins via Perl is with the Device-BCM2835 module from CPAN. It works fine.

In it are very verbose calls to do something (set a pin for input/output, read, write, etc. The following is one.

Device::BCM2835::gpio_fsel(&Device::BCM2835::RPI_V2_GPIO_P1_07, $inputcmd)

So far I have been making a separate hardcoded call for each of the pins that I want to set to input, but that is cumbersome and obviously not the proper way to do such. I want to call this routine with a list of pins, not just number 07 or 19 or whatever. In other words, something like this...

$pinno = RPI_V2_GPIO_P1_07;
Device::BCM2835::gpio_fsel(&Device::BCM2835::$pinno, $inputcmd);
Or even better...
$pinno = "07";
Device::BCM2835::gpio_fsel(&Device::BCM2835::RPI_V2_GPIO_P1_ . "$pinno", $inputcmd)

(I know the above is incorrect. I am just showing what I am trying to do.)

I have been through the topics on aliasing and pointers but I am still not seeing the forest for the trees.

Anybody?

 

[Alexzee]

I'm not good with Perl however; I'm curious and have a question after looking here:

Perl -M will not find a hardcoded path to a module

Background Inside a chsell script, I am invoking a subroutine from a perl module and saving its result to a variable in the following manner: set result =`perl -M/some/hard/coded/path/lib.pm=

stackoverflow.com

Are you trying to invoke a hardcoded module with perl's -M option?

Is BCM2853 by chance a broadcom chip and your trying to make a call for all the pins in a list that pertains to the module?

 

[Alexzee]

Trying to help.....Is this close to what you need?

Device::BCM2835 - Perl extension for accessing GPIO pins on a Raspberry Pi via the BCM 2835 GPIO - metacpan.org

Perl extension for accessing GPIO pins on a Raspberry Pi via the BCM 2835 GPIO

metacpan.org

SPI access requires being root, whereas GPIO access can be done as any user, as the underlying bcm2835 library (which must be installed) can use the /dev/gpiomem interface.

RPi GPIO Code Samples - eLinux.org

elinux.org

 

[CptKrf]

I already use Device::BCM2835. It works fine and my code to access the GPIO pins has no problem with it. But, I apparently didn't make my wants clear.

It isn't that I need help in getting the driver to work, but that I don't quite understand the Perl calls that use it.

To change a pin to input from output something like the following is used...

Device::BCM2835::gpio_fsel(&Device::BCM2835::RPI_V2_GPIO_P1_07, $inputcmd)

It works fine, but is hardcoded to Pin 07. If I want to use pin 13 also, I have to include another hardcoded statement...

Device::BCM2835::gpio_fsel(&Device::BCM2835::RPI_V2_GPIO_P1_13, $inputcmd)

Obviously a clunky way to code, but I can't figure out how to include a variable in the statement so that a loop can access one code line with several pin numbers.

So, not a question on how to make it work, but how to make it work like proper Perl code.

 

[MattWinter]

I'm not familiar with Perl either, but most languages have a way of defining a function.
Can you create your own wrapped function that does what you want? One that accepts an array of values corresponding to pin numbers?

 

[Alexzee]

This Google search looks like a place to start.
The Search included your words:
"How to include a variable in the statement so that a loop can access one code line with several pin numbers"

how to include a variable in the statement so that a loop can access one code line with several pin numbers in perl - Google Search

Our member @JasKinasis writes a lot of scripts. Perhaps he can help.

 

[JasKinasis]

It's been a while since I did any serious Perl. I haven't got time to get myself fully back up to speed with Perl right now either. I'm also unfamiliar with the GPIO module. I know what GPIO is and what it does. I'm just unfamiliar with its Perl interface.

But off the top of my head - assuming you're going to use the same command for each GPIO pin ID, you could simply set up an array of pin ID's and then loop through each pin ID and call the gpio_fsel function, passing each pin reference and the command string:

my $inputCmd = "Your  command string here" # assuming it is a string?!
my @pinIDs = ( &Device::BCM2835::RPI_V2_GPIO_P1_07, &Device::BCM2835::RPI_V2_GPIO_P1_13 ) # Add any other GPIO pin IDs/references here, comma separated!
foreach my $pinID (@pinIDs) {
    Device::BCM2835::gpio_fsel($pinID, $inputCmd)
}

Something like that.

Otherwise, if you're going to use different commands for different pins, you'd have to set up a data structure that holds a GPIO pin ID and a command and then create an array to contain multiple instances of that data structure. But I can't remember how to define structures in Perl offhand, so I'll skip that for now!