Can DTM on nRF52840 be controlled by SPI interface?

[JPierpont]

We currently have a SPI interface between MSP and the Nordic nRF52840. In the DTM documentation it indicates UART is used to command the tests. Is it possible to do this using SPI?j

[Sigurd]

Yes, UART is the de-facto standard. Please take a look at the Bluetooth Core Specification Core version 5.0, page 2773:

Direct Test Mode shall be set up using one of two alternate methods:

1. over HCI (as defined in Section 2) or
2. through a 2-wire UART interface (as defined in Section 3)

Each DUT shall implement one of the two Direct Test Mode methods in order to test the Low Energy PHY layer.

All DTM test software is based on this, and DTM testers, such as the Anritsu MT8852B uses UART. You only need 2 GPIO pins to do UART DTM. Creating a non-standard SPI wrapper to do DTM testing does not seem very advantageous. All authorized test lab that does BLE certification uses UART/HCI.