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7 years ago.
Max value of timer
Hello,
on this link
https://docs.mbed.com/docs/mbed-os-api-reference/en/latest/APIs/tasks/Timer/
is mentioned, that max value of timer is 2^31-1 microseconds. There is also information that timer uses 32-bit int. Now I'm a little bit confused. Why is it 2^31 - 1, when 32 bits are capable of encode 2^32 values? I think max value should be 2^32 - 1 (counting from zero).
Thanks
2 Answers
7 years ago.
Timers return signed values, which is why you lose 1-bit to the sign bit. The reason why it is signed is that it makes it easier to subtract different timer values. While not 100% sure, I believe if you store them in a 32-bit unsigned integer you will get 2^32 range. Tickers however are definitely limited to 2^31 seconds in the future, because they also use signed calculations internally. This is done because they could have occurred in the past (for example if you set up a ticker every 1ms, but then you block with another interrupt for 5ms. Then there are multiple ticker occurrences that happened in the past which need to be handled immediately).
7 years ago.
The "32-bit int" is not "32-bit unsigned int" but "32-bit signed int".
Please refer to https://developer.mbed.org/handbook/C-Data-Types .