FatFSUSB - how to improve speed?

[qqqlab]

I tried this FatFSUSB example to read/write the FAT partition of the Pico flash memory via USB.

It works fine, but I only get around 60 kbyte/sec read/write speeds.

AFAIK Pico uses the USB 1.1 12mbps interface, so theoretically 1500 kbyte/sec should be possible.

Is there a way to improve the speed?

FatFSUSB example:

https://github.com/earlephilhower/arduino-pico/blob/master/libraries/FatFSUSB/examples/Listfiles-USB/Listfiles-USB.ino

Example for a SDCARD connected to a Pico:

https://github.com/qqqlab/qqqlab-RP2040-Toolbox/tree/main/examples/SDCARD-as-USB-memory-stick

[earlephilhower]

You have a couple easy knobs to try. Not sure it's physically possible to get close to 12/8=1.5MB/s with a normal bulk transfer as opposed to ISOC, but you probably can bump it up.

First, make sure you are using 4K sectors. The 512b FTL is more compatible, but there's a lot of indirection needed to make it work. Modern OSes should be able to handle 4K sectors with FAT.

Next, you will want to increase the TinyUSB preallocated MSD buffer size.

arduino-pico/include/tusb_config.h

Line 82 in c5a1255

#define CFG_TUD_MSC_EP_BUFSIZE (64)

(I think 512b maybe the max allowed) . Then rebuild libpico using tools/libpico/makelibpico.sh or the CI action libpico builder in your own private fork of the repo.

You may also be able to use Adafruit_TinyUSB to set the larger buffer, but I've never really looked into it so can't give much guidance.

Beyond that, we really don't have much code in the repo proper in the USB MSD read/write path. Everything is through TinyUSB MSD callbacks, see https://github.com/earlephilhower/arduino-pico/blob/master/libraries/FatFSUSB/src/FatFSUSB.cpp

[qqqlab]

Thanks Earle for your prompt feedback!

I tried to increase the USBD_MSC_EPSIZE buffer size in FatFSUSB.cpp, but it won't compile with that. Did not try to increase CFG_TUD_MSC_EP_BUFSIZE, but it make sense that using a 512 byte vs 64 byte buffer would improve things...

I had more success when I switched to the TinyUSB stack and used the Adafruit TinyUSB "msc_sdfat" example.

Transfer rates are now around 600 kbyte/sec

See also:

Test program: https://github.com/qqqlab/qqqlab-RP2040-Toolbox/tree/main/examples/TinyUSB_msc_sdfat
TinyUSB example: https://github.com/adafruit/Adafruit_TinyUSB_Arduino/tree/master/examples/MassStorage/msc_sdfat
Related discussion: #1505