Intermittent Uart Frame Errors

[tim.fort]

Hello,

I'm running an nrf52832 (fanstel module) communicating over UART with another MCU at 460800 baud. The Uarts both have matching configurations. The baud rates are both set to 460800 using the internal clocks. The UART implementation is similar to the implementation here: https://github.com/nrfconnect/sdk-nrf/blob/main/samples/bluetooth/central_uart/src/main.c however it incorporates a ring buffer.

The UART is receiving a fairly constant stream of data and regularly gets two UART_RX_STOPPED interrupts in a row with reason framing error and then a UART_RX_DISABLED. I've attempted running at lower baud rates of 115200 and 230400 as well with no improvement.

I've analyzed the data sent with a logic analyzer and found that the LA had no errors reading the same uart frames that caused a frame error.

[hmolesworth]

You might also review the definitions for 460800 baud as the earlier nRF52832 documentation was incorrect; perhaps try using 0x075F7000 if not already. However if the "other MCU" device is using the same value as the nRF52832 then of course it doesn't matter what the value is.

//  -------Documentation---------   -------Calculated---------
//  Register    Required   Actual    Register    Actual    Ok?      Index
//  ==========  ========   ======   ==========   ======   ====      =====
   {0x01D60000,   115200,  115108,  0x01D7E000,  115203, "  -"},  // 10
   {0x03B00000,   230400,  231884,  0x03AFB000,  230392, "  -"},  // 11
   {0x04000000,   250000,  250000,  0x04000000,  250000, " Ok"},  // 12
   {0x07400000,   460800,  457143,  0x075F7000,  460800, "  -"},  // 13
   {0x0F000000,   921600,  941176,  0x0EBEE000,  921600, "  -"},  // 14
   {0x10000000,  1000000, 1000000,  0x10000000, 1000000, " Ok"},  // 15
// Extra and changed values from nRF52840 Product Specification
   {0x01D7E000,   115200,  115942,  0x01D7E000,  115203, " Ok"},  // 22
   {0x03AFB000,   230400,  231884,  0x03AFB000,  230392, " Ok"},  // 23
   {0x075F7000,   460800,  470588,  0x075F7000,  460800, " Ok"},  // 24
   {0x0EBED000,   921600,  941176,  0x0EBEE000,  921600, "  -"}}; // 25

nRF52832 v1.7:

// Quoted values from nRF52832 v1.7 datasheet - "No" means incorrect
//
//  --------Calculated-------------------  ---------------Documentation---------------
//  Required Register      Actual   Error  Register    Required   Actual  Error   Ok?
//  ======== =========== ======== =======  =========== ======== ======== =======  ====
//   115200, 0x01D7E000,  115203, +0.002%  0x01D60000,  115200,  115108, -0.079%,  No,
//   230400, 0x03AFC000,  230407, +0.003%  0x03B00000,  230400,  231884, +0.644%,  No,
//   250000, 0x04000000,  250000,       -  0x04000000,  250000,  250000, +0.000%,   -,
//   460800, 0x075F7000,  460800, +0.000%  0x07400000,  460800,  457143, -0.793%,  No,

Edit: I posted my calculation here in case you want to verify:

technical-question-regarding-uart-baud-rate-generator