i2c-1-400kHz.service

[Unit]
Description=Set i2c-1 clock rate to 400kHz

#
# To install:
#     $ sudo cp i2c-1-400kHz.service /etc/systemd/system
#     $ sudo systemctl daemon-reload
#
# To start it:
#     $ sudo systemctl start i2c-1-400kHz
#
# To have it automatically start at boot:
#     $ sudo systemctl enable i2c-1-400kHz
#
# To see the service's output to stdout/stderr:
#     $ journalctl --unit i2c-1-400kHz
#

[Service]
Type=oneshot
ExecStart=/bin/echo 400000
StandardOutput=file:/sys/bus/i2c/devices/i2c-1/bus_clk_rate

[Install]
WantedBy=multi-user.target