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The serial port connection for stm32f4discovery board

Posted by yuanbinzhou on July 8, 2015

Hi!I am new to FreeRTOS,and recently I run FreeRTOS on STM32F4Discovery board,but I found that it is hard to use serial port since there are too many uart pins on this board,so My questions is that how can I successfully connect the "usb to ttl" board to Discovery board(You know that B6/B7,A8/A9 all stands for USART1). IN addition, I change the value of "HSE_VALUE" to 8000000 since the frequency of external crystal is 8MHz.

Another questions is that whether the tickless idle mode is suitable for STM32F4discovery board. Any demos afford?


The serial port connection for stm32f4discovery board

Posted by rtel on July 8, 2015

[Most of your question is not related to FreeRTOS, so would be better posted to an STM32 forum]

The default tickless idle mode can be used on any Cortex-M3/4/7 part, but the power saving it can achieve is limited by two things:

1) The SysTick clock is only 24-bits, and runs very quickly - and therefore overflows often. That limits the maximum tickless period that can be achieved.

2) You cannot enter a very low power state because the really low power modes with stop the SysTick.

Therefore for optimal power saving you will need to create a target specific implementation, such as the one found on the following link:

http://www.freertos.org/STM32L-discovery-low-power-tickless-RTOS-demo.html


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