supervisor.ticks_ms() causes crash

[thirdagemoz]

CircuitPython version

adafruit-circuitpython-adafruit_kb2040-en_US-8.2.10.uf2
adafruit-circuitpython-adafruit_kb2040-en_US-9.1.0.uf2

libs:
adafruit-circuitpython-bundle-8.x-mpy-20240716/
adafruit-circuitpython-bundle-9.x-mpy-20240709/

Code/REPL

import board
import usb_hid
import neopixel

import supervisor
from adafruit_hid.keyboard import Keyboard
from adafruit_hid.keyboard_layout_us import KeyboardLayoutUS

US_SAMPLE_TIME = 500
kbd = Keyboard(usb_hid.devices)
kbd_stream = KeyboardLayoutUS(kbd)

pixel = neopixel.NeoPixel(board.NEOPIXEL, 1)
pixel.brightness = 0.3


# Main loop, check if toe-stud pressed, also constantly measure
# ultrasound distance to foot
cycle = 0
tick_msecs = 0
while True:
    curr_msecs = supervisor.ticks_ms()
    if curr_msecs - tick_msecs > US_SAMPLE_TIME:
        if cycle == 0:
            cycle = 1
            pixel.fill(255)
        else:
            cycle = 0
            pixel.fill(0)

            sense_str = "AAA"
            kbd_stream.write(sense_str)
        tick_msecs = curr_msecs

Behavior

Dies after 1 minute, 5 seconds. No LED flashing or USB keyboard output. Replacing the supervisor.ticks_ms() function with a time.sleep() function runs without fail. I ran on several KB2040, and connected to the USB ports of two different linux machines and a Mac Studio, all fail in exactly the same way. Doing a gc.collect on each loop iteration has no affect. Log file shows only the USB connection occurrence. Adding debug statements points to the while loop failing to restart an iteration, but adding statements after the while loop do not run--it completely locks up. Reset successfully reruns but then fails again after 1 minute and 5 seconds. Erasing the filesystem and restoring the uf2 and libraries and code.py does not fix the problem. Fail exists in both version 8 and 9.

Description

No response

Additional information

No response

[jepler]

To compare two ticks_ms values, you should not use <. Instead, when working with ticks values, use ticks_less, ticks_diff and ticks_add. An implementation suitable to cut&paste is show in the documentation, or you can use the adafruit_ticks library.

The starting point of ticks_ms was chosen so that it would "wrap around" soon after boot, so that users would encounter the problem promptly instead of several days after power-on.

There is more information in the documentation: https://docs.circuitpython.org/en/9.0.x/shared-bindings/supervisor/index.html#supervisor.ticks_ms. Excerpted:

supervisor.ticks_ms() → int
Return the time in milliseconds since an unspecified reference point, wrapping after 2**29ms.

The value is initialized so that the first overflow occurs about 65 seconds after power-on, making it feasible to check that your program works properly around an overflow.

The wrap value was chosen so that it is always possible to add or subtract two ticks_ms values without overflow on a board without long ints (or without allocating any long integer objects, on boards with long ints).

…Addition, subtraction, and comparison of ticks values can be done with routines like the following:

_TICKS_PERIOD = const(1<<29)
_TICKS_MAX = const(_TICKS_PERIOD-1)
_TICKS_HALFPERIOD = const(_TICKS_PERIOD//2)

def ticks_add(ticks, delta):
    "Add a delta to a base number of ticks, performing wraparound at 2**29ms."
    return (ticks + delta) % _TICKS_PERIOD

def ticks_diff(ticks1, ticks2):
    "Compute the signed difference between two ticks values, assuming that they are within 2**28 ticks"
    diff = (ticks1 - ticks2) & _TICKS_MAX
    diff = ((diff + _TICKS_HALFPERIOD) & _TICKS_MAX) - _TICKS_HALFPERIOD
    return diff

def ticks_less(ticks1, ticks2):
    "Return true iff ticks1 is less than ticks2, assuming that they are within 2**28 ticks"
    return ticks_diff(ticks1, ticks2) < 0