i.MX RT1050 EVKB Unable to set LPUART to 460800 baudrate

[jrnTransAct]

(Edit: After changing serial clock source, I can get baud rate set to 460800. I think the issue has to do with my TTL-RS232 converter board not supporting 460800.

So the actual solution for Mbed OS and the RT1050 EVKB eval board was to modify 
\mbed-os\targets\TARGET_NXP\TARGET_MCUXpresso_MCUS\TARGET_MIMXRT1050\TARGET_EVK\mbed_overrides.c serial_setup_clock() as shown below.

)

I'm using an i.MX RT1050 EVKB eval board running Mbed OS 6. I'm trying to set LPUART3 to 460800 baud. However this fails. I can set the baud to anything below that speed. For example, 230400 works great.

Mbed OS 6 calls it's own function serial_baud() which in turn calls an NXP DRIVER function called
LPUART_SetBaudRate() with a serial clock rate of  24000000 that is defined in fsl_lpuart.c.

LPUART_SetBaudRate() returns kStatus_LPUART_BaudrateNotSupport on baud rate 460800.

If I change the serial clock setup so that the serial clock rate is 80000000 by doing the following:

void serial_setup_clock(void)
{
    /* Configure UART divider to default */
    //CLOCK_SetMux(kCLOCK_UartMux, 1); /* Set UART source to OSC 24M */
    CLOCK_SetMux(kCLOCK_UartMux, 0);
    CLOCK_SetDiv(kCLOCK_UartDiv, 0); /* Set UART divider to 1 */
}

then LPUART_SetBaudRate()succeeds. However, this only allows me to properly receive serial data at 460800 baud, but I can't send data at that rate.

Notice in the above code Mbed OS is calling an NXP fsl_clock_config.c function 
CLOCKSetMux(kCLOCK_UartMux, 0) which gives a uart clock rate of 80000000.

Any help on this would be greatly appreciated.
This is being done for a commercial product. If I need to buy a support contract I will, just let me know how to do so.

I've attached fsl_lpuart.c.

[Alexis_A]

Hello @jrnTransAct,

Thanks for sharing your solution.

Best Regards,

Alexis Andalon

[jrnTransAct]

It appears that Mbed OS had specifically changed the LPUART clock source from what NXP had used in their driver. 

With an 80MHz clock I can still use 115200 and 460800. It's unclear to me why the Mbed OS folks wouldn't use the default set up by NXP.