SMT32F767 HSI Clock Calibration

TKana.1 · ‎2024-08-05

Hi,

I am having uart baudrate problems while HSI clock as uart source clock. No problem with PCLK as source with the same uart.

In Cube IDE (V1.16.0) and F7 software package (V.17.2), I get different values for HSI_CALIBRATION:

Ide gets as 0x10 while register (RCC_CR) has 0x68 as HSI_CALIBRATION. The register also has 0x10 for HSI Trim value, which made me confused:

Any pointers which value to use for calibration?

Thanks,

Tim

FBL · ‎2024-08-06

Hi @TKana.1

You can measure the output frequency using an oscilloscope or logic analyze with MCO. Then, you can compare this frequency with the expected HSI frequency to determine if any trimming is needed.

After any reset, trim value is set to 16. Increasing this value by 0x01, increase the period of the oscillator by approximately 0.3% on STM32. AN5067 should explain the calibration principles.

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TKana.1 · ‎2024-08-06

Meant self adjust. On every power up or periodic

Tim

AScha.3 · ‎2024-08-06

Oo...you could set lptim1 on HSI clock and generate a signal ITRx or INT with this, that you measure with any other timer, thats on HSE/PLL clocked .

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