The latest firmware - includes a new config.txt command for configuring pins at boot time. It can be considered an easier alternative to a custom dt-blob.bin for applications that don't need to reassign the named pins (e.g. "LAN_RUN") or create custom clocks.
GPIO control becomes a vital thing in IoT as often setting the state of I/O on boot ensures the commanding and process continuation.
The command is called "gpio", and the syntax is based on the raspi-gpio utility. Each line applies the same settings (or at least makes the same changes) to a set of pins, either a single pin ('3'), a range ('3-4'), or a comma-separated list of either ('3-4,6,8'). The pins are followed by a '=', then one or more comma-separated attributes from this list:
ip - Input
op - Output
a0-a5 - Alt0-Alt5
dh - Driving high (for outputs)
dl - Driving low (for outputs)
pu - Pull up
pd - Pull down
pn/np - No pull
gpio commands are applied in order, so those appearing later override those appearing earlier.
Examples:
# Select Alt2 for GPIOs 0 to 27 (for DPI24)
gpio=0-27=a2
# Set GPIO12 to be an output set to 1
gpio=12=op,dh
# Change the pull on (input) pins 18 and 20
gpio=18,20=pu
# Make 17 to 21 inputs
gpio=17-21=ip
Pins configured by this command are not reserved in any way, so they won't stop kernel drivers or the user-space sysfs GPIO interface from claiming and using them.
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