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:) OMG! Yes. The pins were switched! Because they are switched here https://hackaday.io/project/175577-hackable-nrf52840-smart-watch
The info there is correct, uart is confusing, you typically connect (gps) TX to (nrf) RX, and vice versa.
:) OMG! Yes. The pins were switched! Because they are switched here https://hackaday.io/project/175577-hackable-nrf52840-smart-watch
Now I can set baud rate of NRF UART. But cannot control AT6558.
For some reason. Looks like I need to drain the battery again.
Reading about AT6558 http://www.icofchina.com/d/file/xiazai/2016-12-05/b1be6f481cdf9d773b963ab30a2d11d8.pdf ...
ON_OFF does not turn its power off completely, when it is OFF it will close the RF circuit and baseband circuit, then enter the state of low power consumption.
That is why it remembers settings even after I stop the watch completely and then restart it.
Also AT6558 may be connected in battery backup mode. If so GPS will remember settings until watch battery drained.