A sample code to read SD card, using microcontroller nRF9160.
The code is based on the Arduino SD library (https://github.com/arduino-libraries/SD), and it is modified and redistributed under the GPL-3.0 license.
The library is rewritten in C and adapted to nRF9610, using Segger Embedded Studio.
But as long as the SPI protocol can be accordingly modified, it can be used for any other microcontrollers.
(For example, the code has been modified for STM32 series microcontrollers and it worked well.)
For a fast implementation, the code was written without any consideration in regards to readability or whatever it helps readers to understand the code.
Write functionality is unsupported as well.
It urgently needs a refactoring, a clean-up and pinout description to help understand how it works,
but this is unlikely to happen as the author doesn't have the microcontroller to test it in his possession anymore.