Blink an LED

Blinking an LED is the hardware hello world. It proves three things at once: your host can talk to the board, the board can run Frothy code immediately, and a definition you make at the prompt becomes part of the live image.

Check The Board

Run the environment check first:

frothy doctor

If more than one serial device is visible, pass the port explicitly:

frothy --port /dev/tty.usbserial-XXXX doctor

Then connect:

frothy --port /dev/tty.usbserial-XXXX connect

Configure The Pin

Use the board-provided pin name instead of the raw GPIO number:

gpio.output: LED_BUILTIN

Then drive it by hand:

gpio.high: LED_BUILTIN
ms: 200
gpio.low: LED_BUILTIN

If the LED does not change, stop here. Check the board, the port, and whether your board’s built-in LED is active-high or active-low. Do not hide a wiring or board-selection problem inside a larger definition.

Define A Pulse

At the prompt, define one small word:

to pulse with pin, wait [
  gpio.high: pin;
  ms: wait;
  gpio.low: pin;
  ms: wait
]

Call it once:

pulse: LED_BUILTIN, 120

You should see the LED turn on briefly, then turn off.

If the word is wrong, redefine the same name. You do not need to restart the session.

Build A Blink Word

Now define a repeated blink:

to blink with pin [
  repeat 3 [
    pulse: pin, 120
  ]
]

Run it:

blink: LED_BUILTIN

The important part is not the blink. The important part is that blink lives in the current device image. You can inspect it and change it without reflashing the board.

Redefine It Live

Change the timing:

to blink with pin [
  repeat 5 [
    pulse: pin, 50
  ]
]

Call the same name again:

blink: LED_BUILTIN

The top-level slot named blink stayed stable. Its current value changed. Any later call resolves through that same slot and sees the new behavior.

Inspect it:

show @blink
see @blink
info @blink

Those tools show what the running image currently knows, not what you remember typing ten minutes ago.

Put It On Boot

If you want the board to blink after restore, bind boot to a small setup word:

to boot [
  gpio.output: LED_BUILTIN;
  blink: LED_BUILTIN
]

Keep boot short. Hardware setup and one obvious entry point are fine. A large uninterruptible program is harder to recover from.

Save Or Reset

When you want the overlay image to survive a reboot:

save

If you want to return to the base image:

dangerous.wipe

Use dangerous.wipe intentionally. It clears the saved overlay and the live overlay state.