nRF52 UART connection with constant data stream capability

[Aashay]

Hello, I am working on a project where I have 2 nRF52832 boards with the PCA10040. I have the example developer code examples. I am using the central and peripheral code examples to talk from one UART to another on Tera Term. Although, I noticed that this code is structured so that data is piled in an array and only sent to the other UART when I press "enter" or if it reaches a maximum size (which is very large). I am only using Tera Term to test my boards and not as part of the project. I have an external source of data that works properly on its own and am trying to use these UARTs to establish wireless communication. I have cut the solder bridges SB 22-25 to isolate PO.05 - PO.08 from nRF52832 to the Interface MCU. In pins 6 and 8 on both boards, I put TXD and RXD. Essentially what I am trying to do is have data go though the TXD & RXD wires to one UART, then wirelessly transfer data to the other UART, and have TXD & RXD wires come back. This processes will not work unless the code is structured so that data can be processed (sent & received) continuously. Or at least have it to where whatever is stacked up in the buffer is sent out every interval. I have attached the part of the code for both Central and Peripheral examples that specifically deal with data in UART. I have also put a diagram of sorts to help visualize. Any help would be great. Thanks.

[Vidar Berg]

Hi, you will get higher bandwidth when you split the data into larger chunks as opposed to sending a few bytes at a time (Note: the max data size is defined by m_nus_max_data_len), so it's probably a good idea to accumulate data at a fixed interval before transmitting as you suggested. I would probably have used a longer timer interval though. The lowest connection interval allowed by BT spec. is 7.5 ms anyway. 

Aashay said:

The rest of the data gets lost

 It's not lost by the Softdevice. Data passed to ble_nus_data_send() will be transmitted if the function returns NRF_SUCCESS (i.e., the link will be terminated if a packet is not received within the supervision timeout ). I think it's likely returning NRF_ERROR_RESOURCES as it's easier to fill the Softdevice's TX buffer when you send many small notifications rather than few large notifications. The message for handle value notification illustrates this: https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.s132.api.v6.1.1/group___b_l_e___g_a_t_t_s___h_v_n___m_s_c.html?cp=3_4_1_1_2_4_3_5 

I'd recommend using an app timer instance to control the data transfer. You can use the ble_app_hrs example to see how timers are initialized. 

[Aashay]

Hi, I looked at the ble_app_hrs example. I am still having trouble trying to incorporate a timer instance. If I could get some assistance on what to do, it would be awesome.

[Aashay]

update: so i figured out why i cant use flow control. the program i am using doesn't enable the cts and rts lines in the first place so me trying to enable them is why i was getting the error and wouldnt connect. is there any other way i could increase the how many characters or bits i can pass through the buffer at once? i tested the code with the error handler commented out on tera term and it didnt help increase how many bits i can send through the buffer at once. if i were to put "123456789123" in a .txt file. before it would just handle the error and restart the uart. but now it sends only the first 6 bits so "123456". since i cant use flow control and the error handler doesn't change my results. what other options can i use to increase how much i can pass through my buffer. also why is the buffer being limit to such a small character limit?

[Aashay]

Vidar Berg another update: so with the same code, i am running at different baudrates. at 921600 when i try to send a file .txt, only 6 characters pass through. but when the baudrate is 9600 or even 19200, i can accurately send over 100+ characters without any error. the buffer sizes are 256 for tx and rx. so what could be causing the data to be incomplete at baud rates after 19200?

[Vidar Berg]

Hi,

Were you able to view the debug log from the boards? It should be enough to attach the debugger then open the project in Segger embedded studio and start a debug session. The log should then be shown in the "Debug terminal" view:

Also, can you try the two projects I sent without modifying them and see if you get the same result?  

  

[Aashay]

Hey Vidar Berg, I have a fully functioning code for my central and peripheral uart. I was wondering if it is possible to, and if so how to, make the pairing process secure between the 2 boards. As of now, after I program the examples, the boards just connect automatically and both LED1's turn on. I was wondering if we could make the pairing process start after pressing BUTTON1 on the boards. And then when they successfully pair, the LED1's turn on. And then BUTTON2 would reset the device and disconnect with any paired devices. Any help is great. If you know how to do it or have done something similar, please share in detail or even share your code if you're willing. I have started a new thread, but so far it has been unhelpful because I don't exactly have experience in this. Thanks!! 

[Vidar Berg]

Hi, thanks for linking to the other thread. I can try to integrate the PM module into your projects if you upload them here?

[Aashay]

Vidar Berg, I have uploaded the central and peripheral. I'm sure everything needed is in there. Please let me know if something is missing. Thank you for being a huge help.

Peripheral UART.zip

Central UART.zip

[Vidar Berg]

I have integrated the peer manager and necessary crypto libraries to support LE secure pairing. Please test and review the code.  

231178.zip

[Aashay]

hey Vidar Berg, thanks for helping out. I tried building the project and came upon an unusual building error. I got this for both central and peripheral when i tried building them. 

[Vidar Berg]

Hi, I thought you used Segger embedded Studio so that's what I used. Please try with the two projects I uploaded. It would be a bit time consuming to repeat the process and add all of the required source files and include paths to Keil.  

[Aashay]

Hey Vidar Berg, sorry I should have mentioned that I was using Keil. Regardless, I was able to compile it successfully on segger embedded. I just have some questions on how to alter the code to change what the buttons and leds do.

I wanted the whole process to look like this:

Once the boards turn on, LED1 is off. When BUTTON1 is pressed, it initiates the pairing process (to search for link) on that board. and cant connect unless another board is also in the same searching process. In this process I want the LED1 to be blinking. Once the boards are connected, the LED1 stays on. I want BUTTON2 to be able to completely terminate the link and make the LED1 turn off. And to reconnect, we would repeat the process. 

Is this possible? And where would this be coded/how could it be done?

Thanks so much for all the help.