A simple example of using embedded-sdmmc-rs to write data to an SD card on ESP32 with Rust and Embassy.
- Initializes Micro SD card with automatic retries
- Creates a random CSV filename in the format of "ABC12345.CSV"
- Writes the CSV header "Timestamp,Counter,Value"
- Writes the timestamp and latest counter value to the file every second
- Flushes data every 10 counts to ensure the filesystem's directory entry is updated for this file
- ESP32 development board
- SD card module connected via SPI:
- CS: GPIO18
- SCK: GPIO19
- MISO: GPIO21
- MOSI: GPIO23
There are lots of options for SD card modules. Here are some that we've tested with:
| Link | Image |
|---|---|
| Amazon - HiLetgo 5pcs Micro SD Reader Adapter SPI |  |
| Digi-Key - DFRobot Micro SD Connectivity Evaluation Expansion Board |  |
-
Complete the pre-requisite installations to setup the ESP32 toolchain
-
Build and run to your ESP32
. $HOME/export-esp.sh # Run each time you open a new terminal cargo check # Verify compilation cargo build # Build for target cargo run -r # Use espflash to run on your ESP32
Expand to see Debug output
ets Jul 29 2019 12:21:46
rst:0x1 (POWERON_RESET),boot:0x13 (SPI_FAST_FLASH_BOOT)
configsip: 0, SPIWP:0xee
clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
mode:DIO, clock div:2
load:0x3fff0030,len:6276
load:0x40078000,len:15748
load:0x40080400,len:4
ho 8 tail 4 room 4
load:0x40080404,len:3860
entry 0x4008063c
I (31) boot: ESP-IDF v5.4.1-426-g3ad36321ea 2nd stage bootloader
I (31) boot: compile time Apr 24 2025 15:52:44
I (31) boot: Multicore bootloader
I (34) boot: chip revision: v3.1
I (37) boot.esp32: SPI Speed : 40MHz
I (40) boot.esp32: SPI Mode : DIO
I (44) boot.esp32: SPI Flash Size : 4MB
I (48) boot: Enabling RNG early entropy source...
I (52) boot: Partition Table:
I (55) boot: ## Label Usage Type ST Offset Length
I (61) boot: 0 nvs WiFi data 01 02 00009000 00006000
I (67) boot: 1 phy_init RF data 01 01 0000f000 00001000
I (74) boot: 2 factory factory app 00 00 00010000 003f0000
I (81) boot: End of partition table
I (84) esp_image: segment 0: paddr=00010020 vaddr=3f400020 size=020e0h ( 8416) map
I (94) esp_image: segment 1: paddr=00012108 vaddr=3ffb0000 size=004dch ( 1244) load
I (99) esp_image: segment 2: paddr=000125ec vaddr=40080000 size=01184h ( 4484) load
I (108) esp_image: segment 3: paddr=00013778 vaddr=00000000 size=0c8a0h ( 51360)
I (131) esp_image: segment 4: paddr=00020020 vaddr=400d0020 size=0b274h ( 45684) map
I (147) boot: Loaded app from partition at offset 0x10000
I (147) boot: Disabling RNG early entropy source...
==============================
ESP32 SD Card Counter Example
==============================
Generated filename: R2TBDGCM.CSV
Setting up SPI bus for SD card...
SPI bus configured
Initializing SD Card...
SD Card ready - size: 238 GB
Volume 0 opened
Root directory opened
CSV file 'R2TBDGCM.CSV' created
CSV header written
Starting counter loop...
Counter: 1
Counter: 2
Counter: 3
Counter: 4
Counter: 5
Expand to see R2TBDGCM.CSV file we captured
Timestamp,Counter,Value
234,count,1
1240,count,2
2245,count,3
3250,count,4
4256,count,5
5261,count,6
6266,count,7
7272,count,8
8278,count,9
9284,count,10
10308,count,11
11317,count,12
12323,count,13
13332,count,14
14336,count,15
15340,count,16
16344,count,17
17348,count,18
18352,count,19
19356,count,20
20375,count,21
21384,count,22
22389,count,23
23394,count,24
24400,count,25
25405,count,26
26410,count,27
27416,count,28
We recommend using a tool like Rufus to format the SD card.
| Step | Screenshot |
|---|---|
| 1. Download and install Rufus from https://rufus.ie/ |  |
| 2. Open Rufus and fill out the fields as shown. Ensure you've backed up the data on the SD card before formatting. |    |
| 3. Eject the SD card from your computer |  |
Contributions are welcome! Whether it's bug fixes, feature additions, or documentation improvements, we appreciate your help in making this project better. For major changes or new features, please open an issue first to discuss what you would like to change.