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uart-hello-world

The canonical "printf via UART" walkthrough: open a port with alp_uart_open(), send a greeting plus a monotonically-increasing counter every second, handle the error paths. The producer-only variant most vendor SDKs ship as their first tutorial — uart-echo is the bidirectional companion.

Source: examples/peripheral-io/uart-hello-world/.

Why not just printf?​

Zephyr's printf lands on the console UART — a single, Kconfig-pinned device. Real apps often need to drive a different one: a Bluetooth modem on a secondary port, a GPS module, a stepper driver expecting TMC2209 datagrams, a debug pin that isn't the console.

alp_uart_*() opens any UART by portable instance ID (ALP_E1M_UART0, ALP_E1M_UART1) without touching CONFIG_CONSOLE_*. It also takes a byte buffer plus an explicit length — which is what you want for binary protocols. printf is text-only.

What it does​

  1. alp_init(), then alp_uart_open() on ALP_E1M_UART0.

  2. Builds its config from ALP_UART_CONFIG_DEFAULT(ALP_E1M_UART0) — the macro fills identity from the ID and every other field with its canonical default, which is exactly 115200 8N1. Nothing to override for this app; override a field after the macro when a chip demands different framing:

    alp_uart_config_t cfg = ALP_UART_CONFIG_DEFAULT(ALP_E1M_UART0);
    cfg.baudrate = 9600;   /* then pass &cfg to alp_uart_open */

  3. alp_uart_write() ships a static const greeting with an explicit \r\n — serial terminals expect CR+LF, unlike stdout.

  4. Loops five times: snprintf into a bounded stack buffer, clamp the length (snprintf returns what would have been written), write it, wait a second.

  5. alp_uart_close() releases the SDK handle. It does not power down the controller or drop the line — on real hardware the UART keeps idling high. Use Zephyr's pm_device_action_run after close if you truly need it off.

The example deliberately keeps the raw ALP_E1M_UART0 instance ID in view; uart-echo opens the same port by its board-macro alias. Both styles are first-class.

board.yaml​

som:
  sku: E1M-AEN801

preset: e1m-evk

pins:
  - { e1m: E1M_UART0, macro: EVK_UART_PORT_DEBUG, doc: "Console UART exposed on the debug header" }

cores:
  m55_hp:
    app: ./src
    peripherals:
      - uart

diagnostics:
  log_level: info

The uart entry becomes CONFIG_SERIAL=y in alp.conf, which also activates the SDK's alp_uart_* wrapper layer.

Expected output​

On the SDK log console:

[uart-hello] open ALP_E1M_UART0 @ 115200 8N1
[uart-hello] greeting written
[uart-hello] tick 0 written
[uart-hello] tick 1 written
...
[uart-hello] done

On a terminal attached to ALP_E1M_UART0 itself:

Alp SDK uart-hello-world
tick 0
tick 1
tick 2
tick 3
tick 4

If the port can't open the example prints open failed: alp_last_error=<n> and exits cleanly. Most common causes: no alp-uart0 devicetree alias on this board, or the driver rejected the baudrate/framing combination with -ENOTSUP.

Status​

Runs on native_sim/native/64; the harness latches on [uart-hello] done.

See also​

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