GPIO — Froth

GPIO is the shared digital I/O surface. Use the helper words for ordinary programs, and the raw words when you are documenting or debugging the board boundary.

Availability

Surface	Boards
`gpio.mode`, `gpio.write`, `gpio.read`	ESP32 board profiles and POSIX stubs
`gpio.input`, `gpio.output`, `gpio.high`, `gpio.low`, `gpio.toggle`	Board base libraries

The POSIX target may expose stub behavior so source can be exercised without physical pins. Hardware behavior requires a board target.

Raw Words

gpio.mode: (pin, mode) -> nil

Configures pin direction. 1 means output. 0 means input.

gpio.mode: LED_BUILTIN, 1
gpio.mode: BOOT_BUTTON, 0

gpio.write: (pin, level) -> nil

Writes a digital output level.

gpio.write: LED_BUILTIN, 1
gpio.write: LED_BUILTIN, 0

gpio.read: (pin) -> Int

Reads a digital input level. Most board helpers convert this to a Bool when the electrical meaning is known.

gpio.read: BOOT_BUTTON

Helper Words

The base library defines readable wrappers:

gpio.input: BOOT_BUTTON
gpio.output: LED_BUILTIN
gpio.high: LED_BUILTIN
gpio.low: LED_BUILTIN
gpio.toggle: LED_BUILTIN

Prefer helpers in tutorials and application code. They keep the code about the intent rather than the numeric mode or level.

Active-Low Inputs

Many buttons read 0 when pressed:

to boot.pressed? [
  (gpio.read: BOOT_BUTTON) == 0
]

Name that conversion once. Do not spread active-low electrical details through the rest of the program.