My nRF51822 can not reach 1MBaud on an UART serial UART communication

[Antrou]

Hello,

I am using developping on an nRF51822 with SDK12. In our application, our custom board need to communicate with a computer through a USB communication. I am not using UART over BLE because I do not use BLE in the application, I am then using UART driver for communicating with the computer.

I also use a python script on my computer which sends 10 000 bytes and receives 10 000 through serial communication in order to its real speed. Everything works great when the speed is set to 115 200 kbits/s (Speed observed with python script is close to the theoretical speed) but when I try to set it up to 1Mbaud, I get a observed speed of 300 kbits/s.

I tried to add/remove the fifo on UART driver and also use the scheduler but nothing works and I can't reach the speed we need -> 1Mbaud.

Any suggestion about this problem ? :)

Thank you for your help.

[Hung Bui]

@antrou: Which UART driver you used on the board to communicate with the PC ? Did you test with our nRF51 DK or Dongle ? Our nRFConnect software running on PC use 1Mbps baudrate to communicate with the NRF51 dongle without a problem.

Have you tried on other computer ? I experienced that on some computer 1Mbps baudrate actually not supported.

[Antrou]

Hello,

I am currently using app_uart_put() and app_uart_get() functions with macro APP_UART_INIT as initialization. I only tried our serial speed test on our custom PCB(not DK or dongle) with a nRF51822 processor. I also tried to compute it on another computer but the result remains the same (300 kBaud instead of 1MBaud).

My code and script (which sends/ receives data and compute transfer speed) work really well until 250kBaud, when I try to increase the speed it gets worse and worse ... Any clue will be appreciated :) Thank you for your help.

[Hung Bui]

Can you send me the test firmware you used ? An test to rule out the issue with the computer is to use another nRF51822 to talk to your board. If you have 2 nRF51 board, please try to test. Do you have the 16MHz crystal on your board ? You may want to turn on the 16MHz external crystal instead of using the RC. The RC has pretty high tolerance.

[Antrou]

How can I send you my test firmware ? What is the more suitable for you ? I tried it on 3 differents PCB and the result remains the same. We have a 32MHz crystal on our boards, how can I configure the UART driver in order to use Crystal instead of RC. Thank you

[Antrou]

Our 32MHz crystal is external