app_uart_put() dropping some packets of data on UART

[kumar]

I am working on a project where we are using a nordic bluetooth chip and connecting it to a RS485 Bus using UART with Baudrate 115200. The messages sent from the Bluetooth App should be assembled in the BUS message and should be sent using UART. For this purpose I am using app_uart_fifo.c with the TX_BUFFER_SIZE and RX_BUFFER_SIZE of 1024.

The problem is that I have to send 16 Bytes of data for every Message Frame and as I have checked with the Oscilloscope, there have been only 12 Bytes being sent by the UART Tx channel.

In order to find the problem, I have simply taken the UART example project from Nordic SDK 13.0 version and implemented the example project with a small change. That is, whenever I send anything on Rx characteristic of the nordic nus service, 16 Bytes should be sent on the UART Tx line. To my surprise, it was sending only 12 or 13 bytes everytime I try to send 16 bytes.

Even though the FIFO is 256 Bytes large, why are the Bytes at the end i.e from 13 to 16 being missed. The Baudrate in the example is also set at 115200.

If your Suggestion is to increase the Baud rate, unfortunately I can't because the RS485 Bus is operated at 115200 and supposed to send data at the same speed.

I am literally stuck with this problem and unable to continue with my project. Any Suggestions would be of great help.

Thanks and regards,

Kumar

[Kenneth]

Hi Kumar,

The easiest is to use the nrf UART driver directly, make sure to enable UART0_CONFIG_USE_EASY_DMA, and then each time you want to transmit data call nrf_drv_uart_tx(). If you have enabled a callback handler during nrf_drv_uart_init(), then you will get a event NRF_DRV_UART_EVT_TX_DONE when the transfer is done. In general you can find information about the driver here:

http://infocenter.nordicsemi.com/topic/com.nordic.infocenter.sdk5.v13.0.0/hardware_driver_uart.html?cp=4_0_4_2_18 

The problem with the app_fifo_put is that it was made for the nRF51-series, it still works on the nRF52-series, but it doesn't relly make use of the new EasyDMA feature that came with the nRF52-series.

Best regards,
Kenneth

[kumar]

Hello Kenneth,

Thankyou for your Reply! I found the problem. It lies somewhere else. I have ben using two timers with different timings to generate events on the same hardware pin. The second timer event seemed to disturb the first timer event, thereby distorting my UART tx channel on this common pin. I now have a single timer event for both the cases so that the timer is started at different instances of time.

Regards,

Kumar