Devices

use std.devices

fn main() ! Error uses Serial, Console {
    for path in devices.serial_ports() {
        print(path)
    }
    const board = try devices.open_serial("/dev/ttyUSB0", 115_200)
    try board.write("ping\n".bytes())
    const answer = try board.read(64)
    print(answer.text() ?? "?")
}

It lists the ports, opens one at 115,200 bits a second, sends ping and prints the answer. A port is named as the system names it: COM3 on Windows, /dev/ttyUSB0 on Linux.

• A port runs with 8 data bits, no parity and 1 stop bit, the setting most devices use.
• read waits at most a second for the first byte, and gives empty Bytes when none came. While it waits, the task keeps its turn.
• Each kind of device has a capability of its own, so a function's signature shows what it can reach, and an agent gets one only when a person approves it.

When a port isn't there

DeviceError is NotFound(path), Denied(path) (another program has the port, or the user may not open it) or Failed(path, reason):

use std.devices

fn main() uses Serial, Console {
    const board = devices.open_serial("COM250", 115_200) catch e => {
        print("can't open it: {e}")
        return
    }
    board.close()
}

can't open it: NotFound(path: "COM250")

It needs Serial

A function that reaches a port says so in its uses, or it doesn't compile:

use std.devices

pub fn ports() -> [String] uses Console {
    devices.serial_ports()
}

fn main() uses Console {
    print(ports())
}

error: `ports` uses Serial, but its `uses` clause doesn't list it: add `Serial` to `uses` (spec 8.1)

kavach test has no fake serial port yet, so a function that uses Serial gets no generated tests.