ADXL377 datalogging using Adafruit Feather M0 Express (almost 8 seconds of data with sample rate between 100 and 120Hz, 4 between 200Hz and 210Hz)

boot.py

import storage
storage.remount("/", readonly=True) # to enable the code to save data to the flash this needs to be False

# After the system is reset with the above line set to False, it will not allow to update 
# anything using the virtual USB drive. Therefore it's necessary to connect using the serial USB (minicom),
# enter the REPL (contr+c to cancel code.py if it's running and any key) and paste the line below:
# import os; os.remove("/boot.py"); fs=open("/boot.py", "w"); fs.write("import storage\nstorage.remount(\"/\", readonly=True)"); fs.close()

#
# Usage
#
# The system will blink 3 times (1s each) and it will turn on the red led and start recording. After recording
# it will save the data inside "/data/acc_xxx.bin" with the names incrementing automatically (or it will create
# the first file 001, but the data directory MUST exist).
# The virtual USB drive only updates after ejecting and resetting the uC. After that, just copy and past the files.
# Data is recorded directly using struct.pack('<Qlll'...) so you just need to keep reading until the end of the file:
#
# values = []
# with open(filename, 'rb') as fp:
#     while True:
#         data = fp.read(20) # Qlll => 20 bytes
#         if (not data) or (len(data)<20):
#             break
#         values.append(struct.unpack('<Qlll',data))
# values = np.array(values)
#

code.py

from time import monotonic_ns, sleep

from board import A1, A2, A3, D13
from digitalio import DigitalInOut, Direction
from analogio import AnalogIn

from struct import pack_into

import micropython as mp

from gc import collect, disable, mem_free

from os import listdir

collect()

DCT = mp.const(6) # in seconds

CDBS = mp.const(6) # in seconds

BF = mp.const(910)

DS = mp.const(20)

DD = mp.const("/data/")

# Built in red LED
led = DigitalInOut(D13)
led.direction = Direction.OUTPUT

for i in range(CDBS):
    led.value = not led.value
    sleep(1)


# ADXL377 should be connected to these pins:
x = AnalogIn(A1)
y = AnalogIn(A2)
z = AnalogIn(A3)

fl = listdir(DD)
if fl:
    fl = fl[-1][:-4]
    nf = DD + fl[:-3] + "{:03d}.bin".format(int(fl[-3:])+1)
    del fl
else:
    nf = mp.const(DD+"acc_001.bin")

try:
    disable()
    collect()
    tmp = bytearray(DS*BF)
    tmp_view = memoryview(tmp)
    collect()
    r = range(BF)
    with open(nf, "xb", buffering=0) as fp:
        led.value = True
        total_time_us = int(DCT*1E9 + monotonic_ns())
        collect()
        curr_time = monotonic_ns()
        collect()
        while curr_time < total_time_us:
            collect()
            for i in r:
                curr_time = monotonic_ns()
                collect()
                pack_into('<Qlll',tmp_view,i*DS,curr_time,x.value,y.value,z.value)
                collect()
            fp.write(tmp_view)

finally:
    led.value = False

code2.py

# 
# It goes from 214 to 230Hz and saves ~4s
#

from time import monotonic_ns, sleep

from board import A1, A2, A3, D13
from digitalio import DigitalInOut, Direction
from analogio import AnalogIn

from struct import pack_into

import micropython as mp

from gc import collect, disable, mem_free

from os import listdir

collect()

DCT = mp.const(4) # in seconds

CDBS = mp.const(6) # in seconds

BF = mp.const(900)

DS = mp.const(20)

DD = mp.const("/data/")

# Built in red LED
led = DigitalInOut(D13)
led.direction = Direction.OUTPUT

for i in range(CDBS):
    led.value = not led.value
    sleep(1)


# ADXL377 should be connected to these pins:
x = AnalogIn(A1)
y = AnalogIn(A2)
z = AnalogIn(A3)

fl = listdir(DD)
if fl:
    fl = fl[-1][:-4]
    nf = DD + fl[:-3] + "{:03d}.bin".format(int(fl[-3:])+1)
    del fl
else:
    nf = mp.const(DD+"acc_001.bin")

try:
    disable()
    collect()
    tmp = bytearray(DS*BF)
    tmp_view = memoryview(tmp)
    collect()
    r = range(BF)
    collect()
    with open(nf, "xb", buffering=0) as fp:
        led.value = True
        total_time_us = int(DCT*1E9 + monotonic_ns())
        collect()
        curr_time = monotonic_ns()
        collect()
        while curr_time < total_time_us:
            collect()
            for i in r:
                pack_into('<Qlll',tmp_view,i*DS,monotonic_ns(),x.value,y.value,z.value)
                collect()
            fp.write(tmp_view)
            curr_time = monotonic_ns()

finally:
    led.value = False