能不能用外部32768计算得到内部IRC的准确频率

tianp***

cdp*** 发表于 2024-8-20 05:53
如果已知外部频率,可以参考频率计做法,对外部晶振或其分频做计数,倒推内部时钟误差. ...

在只有单片机的情况下，无法做到内部IRC运行，又对外部RTC分频再引回单片机进行采样

tianp***

还是希望能够找到如C8051F411的捕获外部时钟的类似功能，
这个能很容易在一个计数周期内准确知道内部频率，
且与测量时段保持的足够近

jm***

tianp*** 发表于 2024-8-20 14:39
用RTC的分频中断是个好主意，但无奈这个是个软件方案，非硬件方案，可能也是该款单片机目前最好的方案 ...

Yes, it is a hybrid HW/SW solution.
The SW overhead is modest, just 32 times a second it captures the 2 timer registers and exits.
The SW jitter on the interrupt should be well below the IRC oscillator drift/jitter and if you want to preserve long term drift,  you can read and add the timer values and never clear them.

I still hope to find a similar function like C8051F411 to capture the external clock, which can easily know the internal frequency accurately within a counting cycle and keep it close enough to the measurement period.

yes, STC are not great at cross domain capture, (or indeed much capture at all) so a pure hardware capture is not supported.

tianp***

jm*** 发表于 2024-8-20 15:06
Yes, it is a hybrid HW/SW solution.
The SW overhead is modest, just 32 times a second it captures  ...

这里面最本质的其实就是STC缺少一个RTC的可编程时钟输出，
无论是内部打线还是外部输出，
有了这个硬件上可以做的事情就多了很多。

神***

用 PWM/PCA 功能测量外部 32768 时钟是标准功能

jm***

神*** 发表于 2024-8-20 22:45
用 PWM/PCA 功能测量外部 32768 时钟是标准功能

Do you have diagrams and examples for this ?

jm***

tianp*** 发表于 2024-8-20 15:18
这里面最本质的其实就是STC缺少一个RTC的可编程时钟输出，
无论是内部打线还是外部输出，
有了这个硬件上 ...

You can get 32.768 crystal   X32K/2*N onto a pin, on parts with T11, via T11CLKO

tianp***

jm*** 发表于 2024-8-21 04:30
You can get 32.768 crystal   X32K/2*N onto a pin, on parts with T11, via T11CLKO

{:5_332:}，发现了，最新的8H2K支持T11定时器，这样就可以完美解决