Data throughput between nrf52810 BLE & UART

RE: Data throughput between nrf52810 BLE & UART

sdtjoe — Thu, 12 Mar 2020 11:16:17 GMT

Hi Hung Bui,

Thank you very much!
It's really the problem of interrupt level.
With UARTE, I can use up to 691k baud rate without any problem for Peripheral (UARTE -> BLE) and Central (BLE -> UARTE).

To increase the through put, instead of sending 78 KB per 5ms through BLE, I have set double for it, which is 156 KB per 10 ms.

But then I found another problem.
The distance between the two BLE is very short (about 5 cm).
If it is more then 5cm, the speed will become very slow or even being disconnected.
I think it's strange and should be some setting problem?

Some settings I have changed which may be related:
Tx Power to 4 for Peripheral
Both TX RX Phy is BLE_GAP_PHY_2MBPS for both Peripheral and Central
MIN_CONN_INTERVAL MSEC_TO_UNITS(8, UNIT_1_25_MS)
MAX_CONN_INTERVAL MSEC_TO_UNITS(10, UNIT_1_25_MS)

Thanks,
Joe

RE: Data throughput between nrf52810 BLE & UART

Hung Bui — Wed, 11 Mar 2020 13:25:42 GMT

Hi Joe,
I think it was because the interrupt level. If you call the function inside an interrupt handler with more or equal priority to level 4 it will cause a hardfault.
Please have a look here: https://infocenter.nordicsemi.com/topic/sds_s132/SDS/s1xx/processor_avail_interrupt_latency/exception_mgmt_sd.html?cp=4_5_2_0_15_1

You need to configure the UARTE interrupt level to level 5 or above.

Please try to step into the code and check where you get the assert, it's most likely because of the hvx API call.

RE: Data throughput between nrf52810 BLE & UART

sdtjoe — Wed, 11 Mar 2020 02:47:46 GMT

Sorry but I am quite urgent on resolving the problem of transmitting through BLE.
Could anyone help on this?

Thank you very much.

RE: Data throughput between nrf52810 BLE & UART

sdtjoe — Tue, 10 Mar 2020 07:26:35 GMT

Hi Hung Bui,

Thank you for your suggestion and sample code. I have tried with UARTE and now I am able to receive the data to buffer called uarte_buffer[200].

So the next step is to pass the buffer content to BLE when the interrupt occurs, where NRF_UARTE0->EVENTS_ENDRX == 1.

I have reference the original UART sample code (it's placed in function uart_event_handle, case APP_UART_DATA_READY):

do
{
	uint16_t length = (uint16_t)index;
	err_code = ble_nus_data_send(&m_nus, data_array, &length, m_conn_handle);
	if ((err_code != NRF_ERROR_INVALID_STATE) &&
		(err_code != NRF_ERROR_RESOURCES) &&
		(err_code != NRF_ERROR_NOT_FOUND))
	{
		APP_ERROR_CHECK(err_code);
	}
} while (err_code == NRF_ERROR_RESOURCES);

The above code works correctly , no matter BLE is connected or disconnected.
When not connected it "do nothing"; When connected, it transmit to the connected BLE and I have confirmed I can view the data on the other side.

However with my UARTE:

void send_thru_ble(void)
{
    uint16_t length = (uint16_t)78;	// Data length is always is 78
    uint32_t       err_code;
	
	NRF_LOG_INFO("START: send_thru_ble");
	do
	{
		err_code = ble_nus_data_send(&m_nus, uarte_buffer, &length, m_conn_handle);
		if ((err_code != NRF_ERROR_INVALID_STATE) &&
			(err_code != NRF_ERROR_RESOURCES) &&
			(err_code != NRF_ERROR_NOT_FOUND))
		{
			APP_ERROR_CHECK(err_code);
		}
	} while (err_code == NRF_ERROR_RESOURCES);
	NRF_LOG_INFO("FINISH: send_thru_ble");
}

When the interrupt function (UARTE0_UART0_IRQHandler) being called where NRF_UARTE0->EVENTS_ENDRX == 1, I will call the above send_thru_ble().
When there is no BLE connection, it does not transmit anything and both logs are viewable through RTT Viewer.
However, if the BLE is connected, the system somehow looks hung there, and no log could be seen on RTT Viewer.
I suspect there is some problem when running the ble_nus_data_send, but I don't know how to figure it out.
Because if I set breakpoint on the line err_code = ble_nus_data_send(...), the system will get into NRF_BREAKPOINT_COND; // On assert, the system can only recover with a reset.

The differences of sdk_config.h are the following:
UART:
NRFX_PRS_ENABLED 1
NRFX_UARTE0_ENABLED 0
NRFX_UART_ENABLED 1
UART_LEGACY_SUPPORT 1

UARTE:
NRFX_PRS_ENABLED 0
NRFX_UARTE0_ENABLED 1
NRFX_UART_ENABLED 0
UART_LEGACY_SUPPORT 0

Do you have any hint for me either on:
1. How to debug it this case; or
2. Any setting I have missed to make ble_nus_data_send work?

Best Regards,
Joe

RE: Data throughput between nrf52810 BLE & UART

Hung Bui — Fri, 06 Mar 2020 12:38:45 GMT

Hi Joe,

NRFX_UART is just to support the legacy UART peripheral (no EasyDMA), you can uncheck that.

If you are using ble_app_uart, most likely you are using app_uart for handling UART communication. This library unfortunately not a best choice for application without HWFC and high baudrate.

The reason is that due to the nature of UARTE, you don't receive any event when a byte is received, and you only receive an event when the EasyDMA buffer is full, it has to set the EasyDMA buffer to 1 byte to receive an event for each byte. And this causes the problem when you don't have HWFC and the CPU is busy for BLE. No advantage of using EasyDMA in this implementation.

We have a more advanced UARTE library called libuarte. You can find the example at \examples\peripheral\libuarte. The documentation for the library is here.

This advance library uses a timer to count for the number of byte received. And the async library on top of the driver has a timer to generate a timeout if there is no transaction. The trade off is that more PPI channel and TIMER(s) are needed.

In your case, you have all data fixed to 78 bytes, you can use the driver and don't really need the async library. I think you can also use UARTE directly. An example of using UARTE directly can be found here (the example is for TX, but RX should be similar).

RE: Data throughput between nrf52810 BLE & UART

sdtjoe — Fri, 06 Mar 2020 02:39:30 GMT

Hi Hung Bui,

Thank you for your reply.

I am currently busying on other stuffs, but I have a quick question about #3 first.

As my application is basically a one way NUS (Nordic UART service) from MCU --UART--> BLE ---> BLE --UART--> PC, so I originally expect is just to increase the overall throughput.

The MCU UART only have 2 pin so hardware flow control is not available.
For the peripheral, I am using the example of nRF5SDK160098a08e2/examples/ble_peripheral/ble_app_uart.
For the central, it is ble_central/ble_app_uart_c as its counterpart.
Looks like the ble_app_uart example uses app_uart_fifo, and it takes 1 byte every time until the buffer is empty?

I read several posts on DevZone and figure out that there are some config like NRFX_UART_ENABLED, NRFX_UART0_ENABLED, NRFX_UARTE_ENABLED, NRFX_UARTE0_ENABLED, UART_EASY_DMA_SUPPORT, UART0_CONFIG_USE_EASY_DMA etc.

So my question is:
#3a How do I enable / apply EasyDMA to the example? And how do I confirm if I am using EasyDMA?
Seems just turning on the UART_EASY_DMA_SUPPORT or UART0_CONFIG_USE_EASY_DMA does not change.
I am not quite sure if it is using EasyDMA or not.
Or does the example does not support EasyDMA? so I have to write something myself?
It will be helpful if there is any sample code I could reference.

In sdk_config.h, the UART setting which looks related are as follow:
NRFX_UARTE_ENABLED 1
NRFX_UARTE0_ENABLED 0
NRFX_UART_ENABLED 1
NRFX_UART0_ENABLED 0
UART_ENABLED 1
UART_EASY_DMA_SUPPORT 1
UART_LEGACY_SUPPORT 1
UART0_ENABLED 1
UART0_CONFIG_USE_EASY_DMA 1
APP_UART_ENABLED 1

#3b After looking for the above setting, I am quite confuse with UART, UART0, UARTE, UARTE0.
Can you briefly explain whats the difference?

Thank you very much.

Best Regards,
Joe

RE: Data throughput between nrf52810 BLE & UART

Hung Bui — Thu, 05 Mar 2020 14:22:55 GMT

Hi Joe,

1. Could you please explain how you use UART ? Do you use Easy DMA ? Do you use any of our uart libraries ?

Which UART baudrate did you actually operate at ? We support up to 1Mbps baud.

2. To increase the throughput on BLE, it's important to:

- Transmit as much as possible (queue data as much as possible)

- Low connection interval

- Use Data length extension at least lager than NRF_SDH_BLE_GATT_MAX_MTU_SIZE .

Please check using our \examples\ble_central_and_peripheral\experimental\ble_app_att_mtu_throughput example to test. We observed around 600kbps using 1Mbps BLE PHY and about 1.2Mbps using 2Mbps BLE PHY.

3. It's hard to tell ,if you don't use Easy DMA and if you don't have HWFC missing byte would definitely happens if the CPU is busy doing something else.