How to achieve maximum throughput of UART (virtual COM-Port)

[Maria_19]

Hi all,

I am currently working on a project which uses the ble_app_uart_c example. I have a nRF52840DK as central. The central receives NUS pakets with a average data rate of ~120 kBit/s. Each NUS paket has the same length. 

The received data should be printed on the UART( for accessing it at the COM-Port of a pc). I am using the following parameters for the UART: 

#define UART_RX_BUF_SIZE        32768
#define UART_TX_BUF_SIZE        32768

.baud_rate    = UART_BAUDRATE_BAUDRATE_Baud1M

APP_IRQ_PRIORITY_HIGHEST

My problem is that I still loose some bytes after 1 to 10 minutes. I am using the default for-loop of the ble_app_uart_c example to print the data on the UART.

I already identified that the UART on the central side looses the data. The NUS pakets which I receive are okey.

For my application I am not allowed to loose random bytes. Can you please provide me some help?

Here are my questions:

1. Which parameters provide the highest throughput?

2. How can I prevent a overflow of the uart tx buffer?

3. Is there another way to call app_uart_put(), because I have a defined data_len?

4. How do I achieve a reliable transmission via UART at this 120kBit/s?

Thank you very much in advance.

Kind regards,

Maria

[Vidar Berg]

Hello Maria,

I'd recommend to work with the UART driver directly as that will allow you to use larger DMA buffers. The app_uart implementation is only sending 1 byte at a time and is thus not as efficient in terms of performance.

Kind regards,

Vidar

[Maria_19]

Hi Vidar Berg,

thank you for your quick reply.

I will check the UART driver out. Are there any examples available, regarding how to set this up properly?

I think another approach would be to use flow control, then I could use the default UART implementation of the ble_app_uart_c example. Is flow control over the UART - USB bridge of the nRF52840DK possible? 

Normally RTS and CTS are additional pins on the RS-232.

If my application on my pc allows RTS/CTS flow control, then I could enable flow control by simply setting: APP_UART_FLOW_CONTROL_ENABLED in uart_init()? Is that correct?

Kind regards,

Maria

[Vidar Berg]

Hi Maria,

I see, so the data is being lost by the receiving UART client, right? Flow control may help in that case. It's enabled with the APP_UART_FLOW_CONTROL_ENABLED  setting like you mentioned.

Kind regards,

Vidar

[Maria_19]

Hello  Vidar Berg,

Vidar Berg said:

I see, so the data is being lost by the receiving UART client, right?

yes.

I enabled flow control and it looks promising now. But I have to do further testing. Why is flow control not enabled by default? What are the disadvantages?

Thank you.

Kind regards,

Maria

[Vidar Berg]

Hi Maria,

It's generally better to use flow control. The main drawback with it l is that you have to route out 2 extra pins, and that not all UART clients  support it.

Kind regards,

Vidar