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KL27 LPUART strange baud-rate behaviour

Question asked by Majer on Jan 15, 2016

Ciao to everybody,
a ctm is reporting me a strange behavior (that is replicable on FRDM too) on LPUART of MKL27.

They use:
MKL27Z256VLH4 
      1N71K 
      CTAB1435B
KDS: 3.0.0
KSDK: 1.3.0

They change the baud-rate  with just here after code:
void ChangeUartSpeed(uint32_t xData)
{
  SCI_TI_InitConfig0.baudRate = xData;

  /* UART clock source is either system or bus clock depending on instance */
  uint32_t uartSourceClock = CLOCK_SYS_GetUartFreq(FSL_SCI_TI);

  /* Initialize UART baud rate, bit count, parity and stop bit. */
  LPUART_Type * base = g_lpuartBase[FSL_SCI_TI];
  LPUART_HAL_SetBaudRate(base, uartSourceClock, xData);
}

The result is a baudrate exactely 3 times less than expected, if the clock is the MCG_IRCLK (internal reference one): set for 115200 to obtain 38400.
     OR
The result is a baud-rate half than expected , if the clock is the 48MHz (for the USB): set for 19200 to obtain 38400.

- Remark_1: If the same code is used for the normal UART (not LP), the result is OK.
- Remark_2: If you don't change the default  baud-rate, all is OK.
- Remark_3: the issue is replicable on FRDM-KL27; Attached you can find an "example" where:
          ° to handle the 2 differente baud-rate edit uart_xmad_task.c file (in Source-Interface-UART)
              * at  line 16 the parameter        #define CORR_FACTOR   (1)        is the correrction to obtain the right Baud-rate.
              * at line 54 if you comment the "ChangeUartSpeed" function callng, --> the baud-rate is the one set by Proc.Exp.


I have alredy checked the ERRATA but there was nothing that can explain it.
...may be an SDK issue ?

The questions are:
Do you know it ?
...is HW or SW ?
do you have any workaround ?

The ctm is not so afraid of it ,because they found a way to solve....BUT of course they prefer to work with no "strange" workaround not coming from NXP.

Any suggestion is more than welcome.

Thanks a lot in advance
Franco

Original Attachment has been moved to: x-MAD-TI_FRDM-KL27z.zip

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