First of all I would like to thanks Linuxcnc developers, community members for their endless efforts. Prior to double step we have limited 10Khz step generation for RPI 3B/4B.
But now we have 20Khz step generation, that gives us double the speed for stepper motors.

I remind you this is not my work; I am just sharing ways to achieve in easier way. without wasting time let us start.

Download and install in SD card 16/32 Gb. Its 64 bit Debian
Buster based with 5.10 Rt kernel. Special Thanks to ELOVALVO (LinuxCNC Forum member)
linuxcnc-2.8.2-pi4-arm64.zip

1)    For implementing double step we have to head to second member (tjtr33) and thanks him in advance
for this reality to come true. He gave us hal_pi_gpio.c file to add in LinuxCNC.

for this to work we have to install LinuxCNC rip environment, add this hal_pi_gpio.c file in its relevant place. Compile it Run it.

This gives you deep dive in development, tackling dependancies……..

Build your own .deb package, install and enjoy.

2)    If you wanna shortcut, I have attached .deb file just download the file and copy paste commands in terminal.

First we have to remove installed version as it is single step version.

sudo apt-get remove linuxcnc-uspace

cd Downloads

sudo dpkg -i linuxcnc-uspace_2.8.2_arm64.deb

sudo apt –fix-broken install

Enjoy your double step version.

For further settings in .hal file refer to the below link

https://forum.linuxcnc.org/18-computer/36879-raspberry-pi-4-mmap?start=480

Please do not hesitate to ask for any assistance. I will be happy to help you out.