Bufferedserial skip character when I reduce system clock to 16MHz

Mbed OS
1

Toolchain:
IAR Embeded Workbench ARM
Toolchain version:
9.20.2
MbedOS version:
6.9.0
Target:
nucleo-L476RG

Hi,
I found that bufferedserial skip character after I reduce system clock from 80MHz to 16MHz.
For example, When I send characters like “123456789”, sometimes bufferedserial skip a character like “12356789”.

What I was do to reduce clock is below.

  • Change clock CLOCK_SOURCE setting from USE_PLL_MSI to USE_PLL_HSI in mbed_config.h
  • Configure SetSysClock_PLL_HSI(void) in system_clock.c as below.
    • Change RCC_ClkInitStruct.SYSCLKSource from RCC_SYSCLKSOURCE_PLLCLK to RCC_SYSCLKSOURCE_HSI
    • Change FLASH_LATENCY setting from FLASH_LATENCY_4 to FLASH_LATENCY_0
  • Call SystemCoreClockUpdate() function before setting uart baudrate.

image
image1246×188 115 KB

I found the points things below during I debug this problem.

  • To enter uart interrupt handler is delay because a processing time of LPTIM interrupt handler is long.(around 80us to 90us)
  • The uart interrupt handler execute reading character from RDR and push data to rxbuf, so uart skip a character if to enter uart interrupt handler is delay.
  • LPTIM interrupt handler calls __disable_irq, so uart interrupt handler can’t start process until prosess of finishing LPTIM interrupt handler.
  • hal_critical_section_enter function that calls __disable_irq is weak function.

Can I remove __disable_irq flom the hal_critical_section_enter function?
Could you give me advice to avoid bufferedserial skip character?

Thank you, Soichiro.