MK81 LPUART fail after boot from external qspi flash

[Vladimir_Zitoli]

Dear all,

I am currently developing an application that should be executed from an external QSPI flash. As a starting point, I used the demo project "hello_world_qspi", and followed the procedure described in Paragraph 4 of the document KBLQSPIUG. I also modified the peripheral initializations to suit my setup, specifically using LPUART3 and a GPIO for LED blinking.

The goal of the application is to send a "Hello World" message over the LPUART3 interface at 115200 bps. Although I configured the peripherals using the MCUXpresso Config Tool, I encountered the following issues:

1. The LPUART3 baud rate is not set to 115200 as expected, but instead defaults to 921600. I verified that the microcontroller is correctly executing code from the external QSPI flash.

2. When I attempt to change the LPUART clock source using the function CLOCK_SetLpuartClock(uint32_t src), the application stops working entirely.

I am unsure what is causing these issues. I have attached both the application code and the qspi_config_block.c file for reference. You'll find also the QSPI FLASH datasheet.

Any insights or suggestions would be greatly appreciated.
Looking forward to your feedback.

Kind regards,
Vladimir Zitoli

[Omar_Anguiano · Accepted solution]

If setting the UART baudrate through the function, it approximates to the closest possible value given the clock arguments, so if an incorrect value is set, then it is needed to modify the clock source parameters.
If changing the clock on uart fails, then the reason could be that the selected clock is not init or you are changing the clock at runtime of the module. I suggest changing it before initializing the UART.

Best regards,
Omar