Documentation: initial doc for NRF91

Documentation/platforms/arm/nrf91/boards/nrf9160-dk/index.rst

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+=================
+Nordic nRF9160 DK
+=================
+
+The `nRF9160-DK (PCA10090) <https://www.nordicsemi.com/Products/Development-hardware/nrf9160-dk>`_
+is a development board based on the nRF9160 from Nordic.
+
+Serial Console
+==============
+
+Serial console for the application core:
+
+===== ============ =============
+Pin   Signal       Notes
+===== ============ =============
+P0.28 APP UART0 TX virtual COM 0
+P0.29 APP UART0 RX virtual COM 0
+===== ============ =============
+
+LEDs and Buttons
+================
+
+LEDs
+----
+The PCA10090 has 4 user-controllable LEDs:
+
+====  =======
+LED   MCU
+====  =======
+LED1  P0.02
+LED2  P0.03
+LED3  P0.04
+LED4  P0.05
+====  =======
+
+A low output illuminates the LED.
+
+CONFIG_ARCH_LEDS
+----------------
+
+If CONFIG_ARCH_LEDS is not defined, then the LEDs are completely under
+control of the application.  The following interfaces are then available
+for application control of the LEDs::
+
+  uint32_t board_userled_initialize(void);
+  void board_userled(int led, bool ledon);
+  void board_userled_all(uint32_t ledset);
+
+Pushbuttons
+-----------
+
+=======  =======
+BUTTON   MCU
+=======  =======
+BUTTON1  P0.06
+BUTTON2  P0.07
+=======  =======
+
+Configurations
+==============
+
+Each configuration is maintained in a sub-directory and can be selected as
+follow::
+
+  tools/configure.sh nrf9160-dk:<subdir>
+
+Where <subdir> is one of the following:
+
+nsh
+----
+
+Basic NuttShell configuration (console enabled in UART0, exposed via J-Link VCOM connection,
+at 115200 bps).
+
+ostest_tickless
+---------------
+
+This is a NSH configuration that includes ``apps/testing/ostest`` as a builtin and
+enable support for the tick-less OS.

Documentation/platforms/arm/nrf91/index.rst

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+==============
+ Nordic nRF91
+==============
+
+The nRF91 series of chips from Nordic Semiconductor are based around an ARM Cortex-M33 core
+with integrated LTE-M/NB-IoT modem and GNSS.
+
+Modem Support
+=============
+
+Modem is supported in the nRF91 using Nordic's `Modem library <https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrfxlib/nrf_modem/README.html>`_.
+
+Tool Issues
+===========
+
+OpenOCD
+-------------
+There is no official support for Nordic Cortex M33 chips (nRF9160 or nRF5340).
+
+Segger J-Link
+-------------
+To start the GDB servers for the application core, use these commands::
+
+    JLinkGDBServer -device nRF9160 -if SWD -speed 4000 -port 2331
+
+Then you can connect GDB to targets::
+
+    (gdb) target remote localhost:2331
+
+Supported Boards
+================
+
+.. toctree::
+   :glob:
+   :maxdepth: 1
+
+   boards/*/*