time enhancements - reset epoch, wrapped millis#4935
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* At soft reset, always reset the monotonic epoch. This means that a "fresh" session will not have the accuracy problems that result when `time.monotonic()` becomes a large float and the precision decreases * A new function `reset_monotonic_epoch` in supervisor can reset the epoch to now; Careful use within a program can prevent `time.monotonic()` from losing "too much" accuracy. * A new function `ticks_ms` in supervisor returns the _possibly wrapped_ time since the epoch. The wrapping number is chosen for the reasons given in adafruit#3410: math on these values can be performed in Python without the need to create long integer values (and thus avoids allocations and can work on platforms without longs) It could be argued whether `ticks_ms` should have its epoch reset with the others. I chose not to do so, because programs should be written so that they function properly when `ticks_ms` wraps
… 1 minute of 'boot' .. this will "encourage" software authors to ensure their code works over the wraparound, making it easy (and mandatory) to test. Otherwise, problems might only be seen after 150 hours.
dhalbert
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Jun 27, 2021
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This is a simple set of additions and is elegant. Just one doc typo.
dhalbert
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Jun 27, 2021
| STATIC mp_obj_t supervisor_ticks_ms(void) { | ||
| uint64_t ticks_ms = common_hal_time_monotonic_ms(); | ||
| return mp_obj_new_int(ticks_ms % (1 << 29)); | ||
| return mp_obj_new_int((ticks_ms + 0x1fff7777) % (1 << 29)); |
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I think it would be good to explain this in a comment. It seems like a pretty random number.
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This filled up a couple of m0 builds (non-adafruit products). I turned off rotaryio to let them fit. |
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we may want to decide whether resetting "monotonic" or providing a wrapping ticks_ms is a better use of limited flash, rather than trying to do both. |
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At soft reset, always reset the monotonic epoch. This means that a "fresh" session will not have the accuracy problems that result when
time.monotonic()becomes a large float and the precision decreasesA new function
reset_monotonic_epochin supervisor can reset the epoch to now; Careful use within a program can preventtime.monotonic()from losing "too much" accuracy.A new function
ticks_msin supervisor returns the possibly wrapped time since the epoch. The wrapping number is chosen for the reasons given in RFC: routines for handling wrapped tick counts #3410: math on these values can be performed in Python without the need to create long integer values (and thus avoids allocations and can work on platforms without longs)It could be argued whether
ticks_msshould have its epoch reset with the others. I chose not to do so, because programs should be written so that they function properly whenticks_mswraps