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USB Mass Storage Mode

Overview​

INAV (after 2.3.0) offers USB MSC (mass storage device class) SD card and internal flash access, meaning you can mount the FC (SD card / internal flash) as an OS file system via USB to read BB logs (and delete them from an SD card).

When MSC mode is used with internal flash there are a few differences compared to SD card as it's a virtual file system:

  • The file system is read-only. In order to delete logs it is necessary to erase the flash as usual (configurator, CLI or other tool).
  • The logs are presented as a single, consolidated file (inav_all.bbl) as well as individual logs (inav_001.bbl etc.).
  • Other informative files (e.g. readme.txt) may also exist in the virtual file system.

Usage​

To put the FC in MSC mode:

  • Enter the CLI
  • Enter the CLI command msc ; the FC will reboot
  • Close the CLI tool (cliterm, configurator etc.)
  • Wait for the device to be recognised as USB storage device by the operating system (may take some time, 10-15 seconds perhaps).
  • Copy files off the MSC mounted FC (sd card) (cp, file manager)
  • Dismount / eject the FC (sd card) card using the standard OS method
  • Power-cycle the FC to exit MSC mode.

Performance​

Internal flash is quite fast.

For an SD card, reading is quite slow, typically c. 340kBs, for example:

####################
## Using MSC mode ##
####################
# FC is automounted to /run/media/jrh/BBOX-QUAD by the OS
$ rsync -P /run/media/jrh/BBOX-QUAD/LOGS/LOG00035.TXT /tmp/msclogs/
LOG00035.TXT
     55,856,827 100%  339.15kB/s    0:02:40 (xfr#1, to-chk=0/1)
#########################
## Using a card-reader ##
#########################
# SD Card is automounted to /run/media/jrh/BBOX-QUAD by the OS
$ rsync -P /run/media/jrh/BBOX-QUAD/LOGS/LOG00035.TXT /tmp/sdclogs/
LOG00035.TXT
     55,856,827 100%   19.26MB/s    0:00:02 (xfr#1, to-chk=0/1)

i.e c. 2.5 seconds for the card reader, 2 minutes 40 seconds for MSC (60 times slower). However, if the card is relatively inaccessible, this is a reasonable trade-off

Comparison and Integrity​

The same file (LOG00035.TXT, c 55MB) is copied by MSC to /tmp/msclogs and directly (SD Card Reader) to /tmp/sdclogs.

$ cmp /tmp/{msc,sdc}logs/LOG00035.TXT
# no differences reported ...
$ md5sum /tmp/{msc,sdc}logs/LOG00035.TXT
7cd259777ba4f29ecbde2f76882b1840  /tmp/msclogs/LOG00035.TXT
7cd259777ba4f29ecbde2f76882b1840  /tmp/sdclogs/LOG00035.TXT

You should also be able to run blackbox utilities (e.g. the INAV specific blackbox_decode) without errors on the files, e.g.

$ blackbox_decode --stdout --merge-gps > /dev/null /tmp/msclogs/LOG00035.TXT
Log 1 of 1, start 36:00.888, end 62:00.851, duration 25:59.963

Statistics
Looptime           1006 avg            9.2 std dev (0.9%)
I frames   48405  104.6 bytes avg  5062215 bytes total
P frames  726064   69.2 bytes avg 50246994 bytes total
H frames     380   10.0 bytes avg     3800 bytes total
G frames   15674   21.4 bytes avg   334701 bytes total
S frames    6198   33.0 bytes avg   204534 bytes total
Frames    774469   71.4 bytes avg 55309209 bytes total
Data rate  496Hz  35806 bytes/s     358100 baud

3 frames failed to decode, rendering 4 loop iterations unreadable. 4 iterations are missing in total (4ms, 0.00%)
774472 loop iterations weren't logged because of your blackbox_rate settings (779980ms, 50.00%)

Developer Notes​

Providing MSC is automatically enabled for all F4 and up targets that support ONBOARDFLASH and /or SDCARD.