nrf9160 uart shell echo works on nrf9160dk (SICA B1 2110AM) but not on Thingy91 (SICA B0 1924AP)

[sfrank]

I have two boards, a Thingy91 with "nrf9160 SICA B0 1924AP" and a nrf9160dk with "nrf9160 SICA B1 2110AM". Everything works as expected on nrf9160dk but on the Thingy91 shell echo do not work (i.e. keys pressed in console not visible until I press enter).

it seems that `nrf_uarte_event_check(uarte, NRF_UARTE_EVENT_ENDRX)`, which reads the `ENDRX` register, behaves differently on the two boards. On nrf9160dk it returns for every character received but on Thingy91 it does not return until new line.

Is this a known issue or am I missing something obvious? I have compared .config, .dts and uart register values but found no clues, except that some `RESERVED` uart register have different values between the two boards.

Some relevant configs:

CONFIG_UART_INTERRUPT_DRIVEN=y

CONFIG_UART_ASYNC_API=y

[sfrank]

I have a feeling this is something embarrassing obvious problem, but I really want to know what.

- Same problem with CONFIG_UART_ASYNC_AP=n

- I can reproduce the issue with the shell_modem app (also zephyr/samples/subsys/shell/shell_module). This should not be possible!?

- I have updated to nRF Connect SDK v2.0.0 (had v1.9.{0 or 1} - same problem.

- Tested with `screen` and another serial port application `spcom` - same behavior in both.

- Unplugged the debugger - same problem.