UART access over BLE¶

If you want to receive console output from an updated app, it is possible to do so over the BLE UART Service. For instance, the default app which comes bundled with the bootloader generates regular pings on the rx-characteristic of the UARTService. These pings can be received using one of several UART apps, such as Nordic's nRF UART.

Please be aware that presently it is possible to have only a single active connection to a BLE device; so let's say you're working with a heart-rate application and if you've connected to it using nRF UART for console output, then you cannot simultaneously connect to it from another heart-rate phone app.

Please also note that console messages are sent across in notification packets of up to 20 bytes in size; this limit is imposed by Bluetooth standard. So longer messages need to be cropped into a sequence of 20-byte packets. Output buffers internal to the UARTService are flushed upon encountering a newline character. The receiving UART application should be able to stitch together cropped portions of longer messages.

Using the UART service¶

The following program illustrates the use of UARTService to redirect something like printf() to use the BLE transport.

#if NEED_CONSOLE_OUTPUT
#define DEBUG(STR) { if (uart) uart->write(STR, strlen(STR)); }
#else
#define DEBUG(...) /* nothing */
#endif /* #if NEED_CONSOLE_OUTPUT */


    uart = new UARTService(ble);
    DEBUG("ping\r\n");

You will also need to include UARTService.h.