/*
 * OpenThread RCP on the Seeed XIAO nRF54L15.
 *
 * uart20 (P1.09 TX / P1.08 RX) is wired to the onboard CMSIS-DAP USB-serial
 * bridge, so it is both the board's default console and the only UART that
 * reaches the host over USB. The RCP needs that link for spinel, so:
 *
 *   - zephyr,ot-uart  -> uart20  (spinel to otbr-agent on the host)
 *   - zephyr,console  -> uart21  (moved off, or console output would corrupt
 *                                 the spinel byte stream)
 *
 * uart21 (P2.08 TX / P2.07 RX) is exposed on the XIAO edge pads. Nothing needs
 * to be attached; hook up a USB-UART adapter there if you want boot logs.
 *
 * Unlike Nordic's nrf54l15dk overlay, hw-flow-control is NOT set: the XIAO's
 * pinctrl only defines TX and RX for uart20, and the CMSIS-DAP bridge does not
 * carry RTS/CTS.
 *
 * That missing back-pressure is why the spinel link runs at 460800 rather than
 * the 1000000 Nordic uses. Bandwidth was never the constraint -- 802.15.4 tops
 * out around 250 kbps -- but without RTS/CTS a single late RX interrupt loses a
 * byte outright, and a lost byte corrupts the HDLC frame around it. At 1 Mbaud
 * the driver has 10 us to service each byte; the radio ISR can hold it off
 * longer than that during a burst. 460800 widens the window to 21.7 us while
 * still leaving roughly 4x headroom over peak Thread throughput.
 *
 * The symptom this fixes: otbr-agent runs for hours, then a traffic burst
 * desynchronises the stream, the next transmit gets no response, and
 * HandleRcpTimeout aborts the agent with exit code 6.
 *
 *   [W] P-RadioSpinel-: radio tx timeout
 *   [C] P-RadioSpinel-: Failed to communicate with RCP - no response from RCP
 *
 * The host must agree on the rate. In the RadioURL on the border router host:
 *
 *   spinel+hdlc+uart:///dev/ttyACM0?uart-baudrate=460800
 */

/ {
	chosen {
		zephyr,ot-uart = &uart20;
		zephyr,console = &uart21;
		zephyr,shell-uart = &uart21;
	};
};

&uart20 {
	status = "okay";
	current-speed = <460800>;
};

&uart21 {
	status = "okay";
	current-speed = <115200>;
};