Raspberry: issue configuring GPIO 21 (pin 40) as output

Hello,
it's very strange but if I configure the GPIO 21 that correspond to the pin 40 as output, e.g. Z direction, I get an error opening LinuxCNC.

Message:
./CNC3040.hal:78: Pin 'hal_gpio.pin-40-out' does not exist

It is enabled (GPIO 21) and configured as output of course.

There is something special with this pin I did not know?

Thanks
Bye
Andrea

Thanks for the reply, but as I wrote, (I also new using LinuxCNC and hal config, but..) what happen is that I configured GPIO 21, enabling it (removing mask) and configuring it as output, then when I linked this output to e.g. Z direction, I get the error..
In other words, now it works because I inverted two GPIO, I configured GPIO 20 as output (Z Direction) and GPIO 21 as limit switch (means input).
So.. I'm pretty sure I understood the mechanism, it's the pin 40 (GPIO 21) that doesn't want to be an output! 
I'm asking why and if there is a know reason I didn't get..

mmm, one doubts.. searching again on the web I found this page:
Pinout Raspberry
Now I'm confused.. one pin has 3 different numbers? 
 Should I use 29 in this case?

No.. It can't.. if I look the GPIO 20 it works with 38, not 28..

Searching in this forum for another topic, I found this thread that is explaining the same issue!
forum.linuxcnc.org/24-hal-components/401...river-bug-eventually

The problem was not explained in the thread, only in the hal file attached but the workaround suggested worked also for me.
Strange the bug still since 2020..

Bye
Andrea

Guglielmi wrote:

Searching in this forum for another topic, I found this thread that is explaining the same issue!
forum.linuxcnc.org/24-hal-components/401...river-bug-eventually

The problem was not explained in the thread, only in the hal file attached but the workaround suggested worked also for me.
Strange the bug still since 2020..

Bye
Andrea

Dai uno sguardo qui:
forum.linuxcnc.org/24-hal-components/401...ug-eventually#237353

Ciao