uart_configure() returns -134 (ENOTSUP) w/ 7 data bits on nrf52840dk

[nategreco]

proj.conf:

CONFIG_GPIO=y
CONFIG_SERIAL=y
CONFIG_UART_ASYNC_API=y

nrf52840dk_nrf52840.overlay:

&pinctrl {
	uart1_default: uart1_default {
	   group1 {
		  psels = <NRF_PSEL(UART_TX, 1, 2)>,
				  <NRF_PSEL(UART_RX, 1, 1)>;
	   };
	};
 };
 
 &uart1 {
   compatible = "nordic,nrf-uarte";
   current-speed = <38400>;
   status = "okay";
   pinctrl-0 = <&uart1_default>;
   pinctrl-names = "default", "sleep";
 };

code:

	const struct uart_config uart_cfg = {
		.baudrate = 38400,
		.parity = UART_CFG_PARITY_NONE,
		.stop_bits = UART_CFG_STOP_BITS_1,
		.data_bits = UART_CFG_DATA_BITS_7,
		.flow_ctrl = UART_CFG_FLOW_CTRL_NONE
	};
	ret = uart_configure(uart, &uart_cfg);

Pretty straightforward.  I've looked through the nRF52840 Product Specification and there is no mention of data bits at all, only parity and stop bits, in the UART configuration section.  Does the nRF52840 only support 8-data bits?

If so, that's pretty crushing as I've invested a lot of time and my product requires 7 data bits.  Are there any other nRF SoC's that support 7 data bit UART?

[Sigurd]

Hi,

The UART(E) supports 8-bit data, and 1 or 2 stop bit, and you also change if parity bit is included or excluded.

Are there any other nRF SoC's that support 7 data bit UART?

No

[nategreco]

Thanks for verifying.  yeah, I saw that in the config, but it just omits data bit options and leaves it upon the user to assume it cannot be changed and is fixed at 8 bits.  They should have put a 1-liner there.