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Sub seconds in stm32 f205vet6

Associate II

what is sub seconds ,it is not present in stm32f205vet6 series but mostly on every controller it is present what is the exact use of it how will it make difference

Lead II

Sub seconds is the units of time under 1 second. You can configure any timer to calculate time in seconds or even sub-seconds and generate an interrupt at the end of count.

Best regards.


what makes it different from milliseconds

Pavel A.
Evangelist III

Subseconds is the fractional part. The most significant bit is 1/2 sec, next bit 1/4 s. etc.

Perhaps provide some context, you jump into this assuming we understand your situation or issue.

The Cortex-M3 provides a SysTick which is usually configured for 1000 Hz or 1ms interrupts. These are then typically used to count or mark time for delays, time outs or background tasks.

For 1us granularity it is recommended not to use interrupts, but a free running TIM at 1 MHz whose count you can read and diff. TIM2 and TIM5 should be 32-bit in this context.

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I guess this is about the missing RTC_SSR register in 'F2 RTC.

That register is the exposed counter of synchronous divider, which follows the asynchronous prescaler; these two dividers divide down the 32.768kHz input clock from LSE to the 1 second clock which then advances the rest of RTC (i.e. RTC_TR and RTC_DR).

In other words, it's needed if you for whatever reason want to measure time periods shorter than 1s (or more precisely than with 1s granularity), using RTC. This is a relatively rare requirement. Unless in very-low-power applications, such task can be accomplished using any of the Timers, or the SysTick.