Accompanying Video

ESP32-S3 SD Card Performance Tests - USBMSC and Direct From ESP32

The ESP32-S3 can act as a Mass Storage Class device (USBMSC). This allows us to connect and SD Card to the ESP32 and then access it from a PC.

SD Card Performance Directly Connected to PC

This is just a baseline to see what the SD Card is actually capable of when connected directly to the SD Card reader of my Mac Book Pro.

	Average Speed (B/s)	Average Speed (Mbytes/s)
Write	27,297,357	26.03
Read	94,395,970	90.02

ESP32 <-> SD Card Performance

This test write 100MB of raw sectors to the SD Card and then reads it back. Enable this mode ny uncommenting the line in main.cpp

// #define SD_CARD_SPEED_TEST

All values are in MBytes/s

Operation	1Bit SPI 20 MHz	4Bit SDIO 40 MHz
Write	1.01	2.34
Read	1.67	8.39

USB <-> ESP32 <-> SD Card: Using USBMSC

There are three different configurations in this repo. The basic Arduino code uses the SD class to connect to the SD Card using SPI. This only exposes methods for writing/reading one sector at a time which has a considerable amount of overhead. Using IDF code we can write/read multiple sectors at once. And if we move writing to the SD Card to a background task we can get even better performance - but this comes at the cost of no error handling...

You can switch between these different modes by changing the class used for the SDCard

#ifdef USE_SDIO
  card = new SDCardLazyWrite(Serial, "/sd", SD_CARD_CLK, SD_CARD_CMD, SD_CARD_DAT0, SD_CARD_DAT1, SD_CARD_DAT2, SD_CARD_DAT3);
#else
  card = new SDCardLazyWrite(Serial, "/sd", SD_CARD_MISO, SD_CARD_MOSI, SD_CARD_CLK, SD_CARD_CS);
#endif

You can use the following classes: SDCardLazyWrite, SDCardMultiWrite, SDCardArduino - NOTE - SDCardArduino cannot be used in SDIO mode as the readRAW and writeRAW functions don't exist on the SDMMC class.

Arduino SD Card Code - Single Sector Writing

Type	SPI 20MHz	4Bit SDIO 40 MHz
Write Speed	0.278	NA
Read Speed	0.507	NA

IDF SD Card Code - Multi Sector Writing

Type	SPI 20MHz	4Bit SDIO 40 MHz
Write Speed	0.481	0.66
Read Speed	0.671	1.00

IDF SD Card Code - Multi Sector Lazy Writing

Type	SPI 20MHz	4Bit SDIO 40 MHz
Write Speed	0.915	0.92
Read Speed	0.672	1.00

Summary

Getting up to almost 1MByte/s on both reading and writing is pretty impressive but it probably the best that can be done given the limitations of USB1.1 full speed mode.