| nRF5 SDK v12.0.0 |

Choose documentation: | nRF5 SDK | S130 SoftDevice API | S132 SoftDevice API | S212 SoftDevice API | S332 SoftDevice API

All Data Structures Functions Variables Typedefs Enumerations Enumerator Groups Pages
Direct Test Mode

The DTM application enables the DTM test functions described in Bluetooth Specification Version 4.0, Vol. 6, Part F.

The purpose of DTM is to test the operation of the radio at the physical level, such as:

- Transmission power and receiver sensitivity
- Frequency offset and drift
- Modulation characteristics
- Packet error rate
- Intermodulation performance

# Setup

Test procedures are defined in the document "Bluetooth Low Energy RF PHY Test Specification", Document number RF-PHY.TS/4.0.0. Conformance tests are carried out by dedicated test equipment (such as the Anritsu MT8852 or similar) with the nRF5 with the DTM application as the device under test (DUT).

The nRF5 DTM application includes two parts:

- The DTM - Direct Test Mode library, which manages the nRF radio and controls the standard DTM procedures. The source code for the library can be found in the following folder: `<InstallFolder>\components\ble\ble_dtm`
- An application that provides an external interface to the library. You can find the source code and the project file of the example in the following folder: `<InstallFolder>\examples\dtm\direct_test_mode`

The DTM application contains a driver for a 2-wire UART interface, mapping two-octet commands and events as specified by the BLE DTM specification to the DTM - Direct Test Mode library.

nRF5 with DTM as a DUT

The implementation is self-contained and requires no BLE protocol stack for its operation. The MPU is initialized in the standard way (files `arm_startup_nrf52.s` and `system_nrf52.c` for nRF52 ICs, `arm_startup_nrf51.s` and `system_nrf51.c` for nRF51 ICs). The DTM library function dtm_init configures all interrupts, timers, and the radio.

`main.c` may be replaced with other interface implementations, such as an HCI interface, USB, or another interface required by the Upper Tester.

The interface to the Lower Tester uses the antenna connector of the nRF5. While in principle an aerial may be used, conformance tests cover reading the transmission power delivered by the DUT; hence a coax connection between the DUT and the Lower Tester is employed for all conformance testing.

# BLE DTM module interface

The DTM - Direct Test Mode function dtm_cmd implements the four commands defined by the BLE standard:

- RESET
- RECEIVER_TEST
- TRANSMITTER_TEST
- TEST_END

In the dtm_cmd interface, each of the parameters (cmd, freq, length, payload) is a word size value. Note that the currently supported parameter values are limited to those defined for BLE. (HCI allows a greater value range for use with BR/EDR.)

The following DTM events are polled using the dtm_event_get function:

- PACKET_REPORTING_EVENT
- TEST_STATUS_EVENT [SUCCESS|FAIL]

State machine overview of the DTM

# Vendor Specific packet payload

The BLE 2-wire UART DTM interface standard reserves Packet Type (payload parameter) binary value '11' for a Vendor Specific packet payload. The DTM to Serial adaptation layer maps this to value 0xFFF..FFF in the dtm_cmd interface. The rationale for this mapping is to allow later extensions to a 4-bit Packet Type field, as specified in the HCI interface and in the DTM PDU layout.

The Vendor Specific payload (parameter 4) is interpreted as follows, if parameter 1 (command) is set to Transmitter Test (binary '10') and parameter 4 (payload) to Vendor Specific (binary '11' in the 2wire physical interface, all bits set to 1 in the dtmlib interface):

- If parameter 3 (length) is set to 0 (symbol CARRIER_TEST), an unmodulated carrier is turned on at the channel indicated by parameter 2 (freq). It remains turned on until a TEST_END or RESET command is issued.

- Parameter 3 (length) equal to 1 (symbol CARRIER_TEST_STUDIO) is used by the nRFgo studio to indicate that an unmodulated carrier is turned on at the channel. It remains turned on until a TEST_END or RESET command is issued.

- If parameter 3 (length) is set to 2 (symbol SET_TX_POWER), parameter 2 (freq) sets the TX power in dBm. The valid TX powers are specified for the nRF51 and nRF52 in their respective product specifications ranging from -40 to +4. 0 dBm is the reset value for both. Only the 6 least significant bits will fit in the length field, so the two most significant bits are calculated by the DTM module (which is possible because the 6 least significant bits of all valid TX powers are unique). The TX power can be modified only when no Transmitter Test or Receiver Test is running.

- If parameter 3 (length) is set to 3 (symbol SELECT_TIMER), parameter 2 (freq) selects the timer to be used by the DTM - Direct Test Mode library for Transmitter Test timing. Valid timer identifiers are 0, 1, and 2. Configuring the timer to be used allows the library to be integrated in a larger test environment where other modules may be occupying the default timer (timer 0).

- All other values of parameter 2 (freq) and 4 (length) are reserved.

# The DTM to Serial adaptation layer

`main.c` is an implementation of the UART interface as specified in Volume 6, part F, chapter 3 of the Bluetooth specification.

The default selection of GPIO pins are pin 8 for RX and pin 6 for TX. These defaults are defined in `<InstallFolder>\examples\bsp\board.h` and can be changed by editing the values of the symbols RX_PIN_NUMBER and TX_PIN_NUMBER.

# Running DTM tests

Conformance testing is done using a certified tester. The setup depends on the actual tester, and details about the test operation must be found in the tester documentation. Application note nAN34 describes two alternatives for setting up a production test with DTM: Anritsu MT8852B Bluetooth Test Set, and the nRF8001 Development Kit or the nRF51822 Development Kit together with a computer as the tester.

The BLE DTM UART interface standard specifies:

- 8 data bits
- No parity
- 1 stop bit
- CTS/RTS flow control
- A selection of bit rates from 9600 to 1000000, one of which must be supported by the DUT (It might be possible to run other bit rates through experimenting with parameters.)

The default bit rate of the DTM UART driver is 19200 bps, which is supported by most certified testers.