enable FF_USE_FASTSEEK

[michael-betz]

This might be more of an esp-idf feature request, but Arduino is also affected as the pre-compiled esp-idf libraries are used and there is no easy way to modify them.

Without FF_USE_FASTSEEK, seeking backwards or forwards on a FAT32 FS takes hundreds of ms.

This shows up, for example, when streaming animations from a SD card and frames need to be shown in a non-sequential way.

Enabling FF_USE_FASTSEEK costs ~64 words of memory per open file and reduces seek time by a factor of ~100.

I tested this by overriding the ff.c file with my patched version:
michael-betz/espirgbani_pio@2c957e3

See also:
http://www.elm-chan.org/fsw/ff/doc/lseek.html

[michael-betz]

Here is a benchmark project:
https://github.com/yetifrisstlama/fast_seek_test

Needs platform.io and an ESP32 with SD card connected.

------------------------
 without FAST_SEEK
------------------------
[I][main.cpp:34] setup(): Creating 200 MB file: /sd/test.dat ...
[I][main.cpp:58] setup(): fseek( 104857750) dt: 128002 us, read 4096
[I][main.cpp:58] setup(): fseek( 104857751) dt: 128022 us, read 4096
[I][main.cpp:58] setup(): fseek( 104857752) dt: 128044 us, read 4096
[I][main.cpp:58] setup(): fseek( 104857753) dt: 128061 us, read 4096
[I][main.cpp:58] setup(): fseek( 104857754) dt: 128012 us, read 4096
[I][main.cpp:58] setup(): fseek( 104857755) dt: 127987 us, read 4096
[I][main.cpp:58] setup(): fseek( 104857756) dt: 128001 us, read 4096

------------------------
 with FAST_SEEK enabled
------------------------
(comment last line in platform.ini)
[I][main.cpp:34] setup(): Creating 200 MB file: /sd/test.dat ...
[V][ff.c:3736] f_open(): FAST_SEEK enabled
[I][main.cpp:58] setup(): fseek( 104857750) dt:   1143 us, read 4096
[I][main.cpp:58] setup(): fseek( 104857751) dt:    692 us, read 4096
[I][main.cpp:58] setup(): fseek( 104857752) dt:    684 us, read 4096
[I][main.cpp:58] setup(): fseek( 104857753) dt:    681 us, read 4096
[I][main.cpp:58] setup(): fseek( 104857754) dt:    679 us, read 4096
[I][main.cpp:58] setup(): fseek( 104857755) dt:    682 us, read 4096
[I][main.cpp:58] setup(): fseek( 104857756) dt:    681 us, read 4096

[PrintEngineering]

This sort of thing should get more attention. I was looking for answers to something else, but I was happy to stop and read this along the way.

[lbernstone]

This is an upstream issue. If someone opens the issue at https://github.com/espressif/esp-idf/issues, it can be added. It's not fixable here.

[stale]

[STALE_SET] This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 14 days if no further activity occurs. Thank you for your contributions.

[stale]

[STALE_DEL] This stale issue has been automatically closed. Thank you for your contributions.