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Arm Mbed OS is a platform operating system designed for the internet of things
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Serial corruption on STM32L4 at 115200 baud #67

Open multiplemonomials opened 1 year ago

multiplemonomials commented 1 year ago

It seems like the STM32L4 is experiencing quite serious corruption on its UART transmissions when run at 115200 baud. This is enough to make a few test cases out of each run fail due to missed control messages. Need to look into what's causing this

multiplemonomials commented 1 year ago

I think this might be an oscillator problem on my dev board. Adding 

        "STM32L452xE": {
            "target.clock_source": "USE_PLL_HSI"
        }

to mbed_app.json seems to fix it. Additionally, I bought a new logic analyzer that is capable of taking long-duration captures, and managed to zoom in on the bytes where an issue is happening: image image The 'p' byte is supposed to be a '0', but an additional 4us have been added into the logic low in the first half of the byte. This shifts the MSBits over by one, making it the wrong character. I did not find anything in the code, datasheet, or errata explaining this -- it's like the UART bit clock just stopped for a few microseconds. So, I suspect that maybe there's something up with the crystal oscillator that's causing its clock to slow down or stop for a few microseconds intermittently.

JojoS62 commented 1 year ago

have you checked the frequency of the oscillator? You can output the clock on gpio pin, check system_clock.c in the target files for DEBUG_MCO or HAL_RCC_MCOConfig.