nrf-ble-uart-low-latency-bridge

System overview

This repository demonstrates how the nRF52-series can be used be as a UART/BLE bridge, with low latency. The FW provided in this repository is based on examples from the nRF SDK v16.0.0

ble_app_uart example for the nRF52 BLE Peripheral
ble_app_uart_c example for the nRF52 BLE Central
libuarte example for UART handling, and the nRF 52 round trip time tester (see below)

Hardware flow control is not used for UART handling. The system currently uses baudrate 1M (1000000).

Tune to increase performance

This setup is not battery optimized, nor fully latency optimized. One could concider to include HW flow control to increase response time instead of the libuarte async timeout.

To inrease performance even slightly more, disable logging in the projects sdk_config.h

#define NRF_LOG_ENABLED 0

Test system latency

This repository includes a round trip time test code based on the libuarte example from the nRF SDK v16.0.0. This FW is tested with the nRF52840, built with Segger Embedded Studio.

The tester transmits 100 messages, each containing 100 bytes, in both directions. A timestamp is included in the message which is used to calculate the round trip time for each message. After 100 messages are sent in both directions, the average round trip time is reported reported through the logging module.

Real Time Transfer (RTT) is used as logging backend. The logs provides status of number of messages that were transmitted around the system OK and their round trip time. The averarge round trip time in both directions are calculated.

Build FW

To build the projects with nRF SDK16.0.0, place this repo two folder levels below the sdk_root level.

sdk_root/my_projects/nrf-ble-uart-low-latency-bridge/ble_app_uart/
sdk_root/my_projects/nrf-ble-uart-low-latency-bridge/ble_app_uart_c/
sdk_root/my_projects/nrf-ble-uart-low-latency-bridge/libuarte/

Supported devices and IDEs

The FW is in its current shape only tested with the nRF52832 as the UART/BLE bridges, and with the nRF52840 for the UART Round Trip Time tester. It should be possible to use all nRF52 devices for the UART/BLE bridges, with different SoftDevices.

Project	Device	SoftDevice	IDE
BLE Peripheral	nRF52832	s132	SES and Keil
BLE Central	nRF52832	s132	SES and Keil
Round Trip Time tester	nRF52840		SES

Add support for other devive/IDE

To add support for another device or IDE, please copy the project files from the respective SDK example and update the following.

Include the listed files and paths:

Paths:

.\..\..\..\..\..\components\libraries\libuarte\
..\..\..\..\..\..\components\libraries\queue

Files

..\..\..\..\..\..\components\libraries\libuarte\nrf_libuarte_async.c
..\..\..\..\..\..\components\libraries\libuarte\nrf_libuarte_drv.c
..\..\..\..\..\..\components\libraries\queue\nrf_queue.c

..\..\..\..\..\..\modules\nrfx\drivers\src\nrfx_timer.c
..\..\..\..\..\..\modules\nrfx\drivers\src\nrfx_ppi.c

Remove files from project:

Remove all existing UART c-files, e.g. nrf_drv_uart.c, app_uart_fifo.c
Remove retarget.c

Upadate the sdk_config.h if needed with the following:

NRFX_TIMER_ENABLED 1
NRFX_TIMER1_ENABLED 1
NRFX_TIMER2_ENABLED 1
NRFX_TIMER3_ENABLED 1
NRFX_TIMER_DEFAULT_CONFIG_BIT_WIDTH 3

Remove old legacy NRF_TIMER

NRFX_PPI_ENABLED 1

Remove old legacy NRF_PPI

NRF_QUEUE_ENABLED 1

NRF_LIBUARTE_ASYNC_WITH_APP_TIMER 0
NRF_LIBUARTE_DRV_HWFC_ENABLED 0
NRF_LIBUARTE_DRV_UARTE0 1

UART_ENABLED 0
APP_UART_ENABLED 0
NRFX_UART_ENABLED 0
NRFX_UARTE_ENABLED 0

If it still doesn't compile, please diff your sdk_config.h against the ones from the tested setups.

prestegaard / nrf-ble-uart-low-latency-bridge