How to use the "arduino-samd21lpe" patches with PlatformIO, (Linux only):

[RatGit]

Run these bash commands:

pio_user="${USER}" # User that you will be running PlatformIO with
package_folder="/home/${pio_user}/.platformio/packages"
patch_folder="/path/to/where/you/downloaded/arduino-samd21lpe-main/arduino-samd21lpe-main/patches/Seeduino-hardware-samd-1.8.3"

rm -rf "${package_folder}/framework-arduino-samd-seeed-lpe" # Remove if previously installed

cp -as "${package_folder}/framework-arduino-samd-seeed" "/tmp/" # Copy as soft links to temporary location

mv "/tmp/framework-arduino-samd-seeed" "${package_folder}/framework-arduino-samd-seeed-lpe" # Rename in correct location

Patch "startup.c"

rm "${package_folder}/framework-arduino-samd-seeed-lpe/cores/arduino/startup.c"
cp "${patch_folder}/startup.c" "${package_folder}/framework-arduino-samd-seeed-lpe/cores/arduino/startup.c"
chmod a+r,a+w "${package_folder}/framework-arduino-samd-seeed-lpe/cores/arduino/startup.c"

Patch "boards.txt"

rm "${package_folder}/framework-arduino-samd-seeed-lpe/boards.txt"
cp "${patch_folder}/boards.txt" "${package_folder}/framework-arduino-samd-seeed-lpe/boards.txt"
chmod a+r,a+w "${package_folder}/framework-arduino-samd-seeed-lpe/boards.txt"

Rename package to "framework-arduino-samd-seeed-lpe"

rm "${package_folder}/framework-arduino-samd-seeed-lpe/package.json"
cp "${package_folder}/framework-arduino-samd-seeed/package.json" "${package_folder}/framework-arduino-samd-seeed-lpe/package.json"
sed -i 's|"name":[[:space:]]*"framework-arduino-samd-seeed"|"name": "framework-arduino-samd-seeed-lpe"|' "$package_folder/framework-arduino-samd-seeed-lpe/package.json"

chown -hR "${pio_user}:${pio_user}" "${package_folder}/framework-arduino-samd-seeed-lpe" # Change ownership to PlatformIO user

Edit "platformio.ini":

build_flags = -DF_CPU=48000000L ; You can change this to other frequencies
platform_packages =
framework-arduino-samd-seeed @ file:///home/<pio_user>/.platformio/packages/framework-arduino-samd-seeed-lpe ; Force compiler to use the LPE framework
framework-arduino-samd-seeed-lpe @ file:///home/<pio_user>/.platformio/packages/framework-arduino-samd-seeed-lpe
; Note: Change <pio_user> to actual PlatformIO user name

Notes:

1. Don't forget to re-do this procedure after a PlatformIO update

[RatGit]

Alternative Method

You can also fork the "https://github.com/Seeed-Studio/ArduinoCore-samd" repository then modify and commit the "startup.c", "boards.txt" and "package.json" files and finally reference this in your "plaformio.ini" file like this:

platform_packages =
framework-arduino-samd-seeed @ file:///home/<pio_user>/.platformio/packages/framework-arduino-samd-seeed-lpe ; Force compiler to use the LPE framework
framework-arduino-samd-seeed-lpe @ https://github.com/RatGit/ArduinoCore-samd-lpe.git ; My fork

• This approach will ensure that PlatformIO updates will happen automatically when the "ArduinoCore-samd-lpe" repository is updated and that the "package.json" file has a valid URL.

I'd like to be able to remove the "platformio.ini" file entry that maps the "framework-arduino-samd-seeed" framework to "framework-arduino-samd-seeed-lpe", but currently haven't figured how else to stop the "atmelsam" platform and "seeed_xiao" board auto-selecting the "framework-arduino-samd-seeed" framework?

[RatGit]

How to Create PlatformIO Low Power versions of the Arduino SAMD Core Frameworks: (for Seeed Studio and Arduino devices)

(Final Method)

Clone the original Arduino SAMD Core repositories:

framework_folder="/home/<pio_user>/Documents/LPE"
mkdir "${framework_folder}"; cd "${framework_folder}"
git clone 'https://github.com/arduino/ArduinoCore-samd.git' framework-arduino-samd-lpe
git clone 'https://github.com/Seeed-Studio/ArduinoCore-samd.git' framework-arduino-samd-seeed-lpe

Modify the "./cores/arduino/startup.c" files with the Low Power Modifications: (You can Diff the following file pairs from my personal repo for changes)
framework-arduino-samd:startup.c | framework-arduino-samd-lpe:startup.c
framework-arduino-samd-seeed:startup.c | framework-arduino-samd-seeed-lpe:startup.c

Modify the "./package.json" files, changing the "name" and "url" values to the new "LPE" version: (Diff the following file pairs for changes)
framework-arduino-samd:package.json | framework-arduino-samd-lpe:package.json
framework-arduino-samd-seeed:package.json | framework-arduino-samd-seeed-lpe:package.json

Create two new repositories on GitHub:
https://github.com/<github_user>/framework-arduino-samd-lpe
https://github.com/<github_user>/framework-arduino-samd-seeed-lpe

Initial commit and remote push of repositories:

cd "${framework_folder}/framework-arduino-samd-lpe"
git remote add GitHub ssh://git@GitHub/<github_user>/framework-arduino-samd-lpe.git
git init .
git commit -a -m 'Initial Commit'
git push GitHub --all
git push GitHub --tags

cd "${framework_folder}/framework-arduino-samd-seeed-lpe"
git remote add GitHub ssh://git@GitHub/<github_user>/framework-arduino-samd-seeed-lpe.git
git init .
git commit -a -m 'Initial Commit'
git push GitHub --all
git push GitHub --tags

Get PlaformIO to Update Frameworks, (using the "platformio.ini" file):

platform_packages =
framework-arduino-samd-lpe @ https://github.com/<github_user>/framework-arduino-samd-lpe.git ; Update from the Arduino LPE repository
framework-arduino-samd-seeed-lpe @ https://github.com/<github_user>/framework-arduino-samd-seeed-lpe.git ; Update from the SeeedStudio LPE repository

Force PlatformIO to compile against the LPE frameworks, (using the "platformio.ini" file):

platform_packages =
framework-arduino-samd @ file:///home/sysadmin/.platformio/packages/framework-arduino-samd-lpe ; Force compiler to use the LPE framework
framework-arduino-samd-lpe @ https://github.com/<github_user>/framework-arduino-samd-lpe.git ; LPE Fork

platform_packages =
framework-arduino-samd-seed @ file:///home/sysadmin/.platformio/packages/framework-arduino-samd-seeed-lpe ; Force compiler to use the LPE framework
framework-arduino-samd-seeed-lpe @ https://github.com/<github_user>/framework-arduino-samd-seeed-lpe.git ; LPE Fork

Copy the "https://github.com/jnsbyr/arduino-samd21lpe/src" source files to the project folder:
./lib/samd21lpe/Analog2DigitalConverter.cpp
./lib/samd21lpe/Analog2DigitalConverter.h
./lib/samd21lpe/RealTimeClock.cpp
./lib/samd21lpe/RealTimeClock.h
./lib/samd21lpe/System.cpp
./lib/samd21lpe/System.h
./lib/samd21lpe/TimerCounter.cpp
./lib/samd21lpe/TimerCounter.h

Notes:

• Change <pio_user> to actual PlatformIO user name
• Change <github_user> to actual GitHub user name
• The "GitHub" host used when adding and pushing to a remote repository, eg. "git remote add GitHub" and "git push GitHub", is defined in "~/.ssh/config" like this:
  (BTW: You can just ask ChatGPT "How do I create and add an SSH key pair for GitHub?")

Host GitHub
        User <github_user>
        Hostname github.com
        IdentityFile ~/.ssh/github_ed25519
        TCPKeepAlive yes
        IdentitiesOnly yes