Accessing little file storage data over BLE

RE: Accessing little file storage data over BLE

Einar Thorsrud — Sun, 20 Nov 2022 11:20:22 GMT

Hi Mike,

I am no littlefs expert, but if I understand the question correctly, then yes, you can append as well as update or overwrite (parts of) files, or a combination of that. (This is conceptually seen from the littlefs APIs though, so when you close the file and it is actually written to flash, it will be re-written to a new physical location).

RE: Accessing little file storage data over BLE

Mike Austin (LPI) — Thu, 17 Nov 2022 04:18:16 GMT

Hi Einar,

Thanks - turns out my App developer was doing something wrong. We've got this part of it working now.

A question for you on using lfs - we are trying to log data into the file storage so that we have a record of events. Our hardware spends most of its time in SYSTEM_OFF mode. When triggered by a GPIO, it will wake up, record date/time and event type and event value, write this to file storage, then go back into deep sleep.

I'm still building all this functionality, but what I wanted to know is whether its possible to append new data to the existing data within my file on littlefs, or do I need to read in the contents of the file into a local struct, update the data, then write the whole lot back to the file before going back into deep sleep?

Cheers,

Mike

RE: Accessing little file storage data over BLE

Einar Thorsrud — Thu, 10 Nov 2022 15:15:22 GMT

Hi Mike,

MGMT_ERR_ENOENT is what you would get if you try to open a file that does not exist, so the path or mount point seems to be wrong.

If you don't make progress, I suggest experimenting a bit with the SMP Server Sample. That support a number of different backends, including Bluetooth and serial. For instance, by taking that sample from nRF Connect SDK SDK 2.1.2 and building with two additional configuration files (overlay-fs.conf and overlay-serial.conf) I got a working sample that makes it easy to demonstrate. Here I am both writing and reading back a file using mcumgr (serial here for simplicity, but the transport should not matter):

$ echo "Test test" > test.txt
$ mcumgr -c acm0 fs upload test.txt /lfs1/test.txt
10
Done
$ mcumgr -c acm0 fs download /lfs1/test.txt test_readback.txt
0
10
Done
$ cat test_readback.txt 
Test test

PS: The first time you use a COM port with MCUmgr with a serial port you need to configure it. For my setup this was right, but you may need to do something differently:

mcumgr conn add acm0 type="serial" connstring="dev=/dev/ttyACM0,baud=115200,mtu=512"

Einar