Generate Software Interrupt (SI) with STM32F· Discovery board with HAL drivers
likely you timer isnto configure corretcly
it is common to get the auto reloade or prescalewrong due to divider ( timer input clock is 2x the ahb clk)
25HZ 40ms
also they are a few +/- 1 to consider in the prescaler and ARR valeu that can make huge diffrence in final timer freq
i recomend you read http://www.st.com/web/en/resource/technical/document/application_note/DM00042534.pdf
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