What is eMMC (Embedded MultiMediaCard) memory ?

What is eMMC ?

eMMC stand for Embedded Multi Media Card) memory , eMMC is a type of non-volatile flash storage which used in embedded systems. eMMC is combination of NAND flash memory and a flash memory controller in a single package, so both NAND and flash memory in single bundle eMMC provide simple and very cost-effective storage solution in embedded domain .

List of 6 Key Features of eMMC Memory in embedded domain:

• Power Efficiency: eMMC memory consumes less power, that’s makes it ideal for battery-powered devices.
• Embedded Storage: eMMC memory is on board solution its not like removable SD cards form device, eMMC is soldered directly onto the PCB, that’s makes part of PCB itself
• Managed Flash Memory: It includes an integrated controller that manages wear leveling, bad block management, and error correction, reducing the complexity for the host system.
• Standardized Interface: eMMC follows JEDEC (Joint Electron Device Engineering Council) standards such as eMMC 5.1, eMMC ensure compatibility across devices.
• Capacity: eMMC come under typically ranges from 4GB to 128GB, but in some higher-end models it reaching 256GB or more then that.
• Performance: Basically its slower than SSD but comparatively more faster than traditional SD cards, with speeds goes up to 400 MB/s in eMMC 5.1 version

Applications of eMMC in Embedded Systems:

• Used in Smartphones and tablets
• Used in Industrial and automotive embedded systems
• Used in IoT devices
• Used in Medical equipment
• Used in Consumer electronics such as smart TVs

Comparison with Other Storage Technologies:

Feature	eMMC	SSD	SD Card
Speed	Moderate	High	Low
Interface	Parallel	PCIe and SATA	Serial
Removability	No	No for most of the Case	Yes
Cost	Low	Higher	Low
Power Usage	Low	Moderate	Low

Limitations of eMMC:

• eMMC is bit Slower than SSD
• eMMC is not designed for high-end performance applications.
• eMMC having limited lifespan as compared to enterprise level different storage solutions.

Practically Example

Let Do Practically Example by Interfacing eMMC with STM32F407VG for understanding in depth : Interfacing eMMC with STM32F407VG requires understanding way to communicate with the memory using the SDIO also called Secure Digital Input Output interface or SPI also called Serial Peripheral Interface

Steps to Interface eMMC with STM32F407VG

1. Hardware Connections

• The STM32F407VG has an SDIO (Secure Digital Input Output) peripheral, which can be used to communicate with eMMC.
• eMMC uses an 8-bit parallel interface, but STM32 SDIO supports only a 4-bit mode.
• Use level shifters if needed, as eMMC typically operates at 1.8V or 3.3V, while STM32F407VG GPIOs are 3.3V.

SDIO Pin Mapping for STM32F407VG

eMMC Pin	SDIO Pin on STM32F407VG	Alternate Function
CMD	SDIO_CMD (PA6)	AF12
CLK	SDIO_CK (PC12)	AF12
DAT0	SDIO_D0 (PC8)	AF12
DAT1	SDIO_D1 (PC9)	AF12
DAT2	SDIO_D2 (PC10)	AF12
DAT3	SDIO_D3 (PC11)	AF12
VCC	3.3V or 1.8V	Power
VSS (GND)	GND	Power

2. Software Development

To communicate with eMMC, you need to configure SDIO and use a file system like FATFS (if using a file system) or send raw commands.

2.1 Enable SDIO in STM32CubeMX

1. Open STM32CubeMX.
2. Select STM32F407VG.
3. Enable SDIO in 4-bit wide bus mode.
4. Configure the clock to 48 MHz.
5. Enable DMA for SDIO for better performance.

2.2 Implement eMMC Initialization in STM32CubeIDE

1. Initialize SDIO Peripheral

#include "stm32f4xx_hal.h"
SD_HandleTypeDef hsd;

void MX_SDIO_SD_Init(void) {
    hsd.Instance = SDIO;
    hsd.Init.ClockEdge = SDIO_CLOCK_EDGE_RISING;
    hsd.Init.ClockBypass = SDIO_CLOCK_BYPASS_DISABLE;
    hsd.Init.ClockPowerSave = SDIO_CLOCK_POWER_SAVE_DISABLE;
    hsd.Init.BusWide = SDIO_BUS_WIDE_4B;
    hsd.Init.HardwareFlowControl = SDIO_HARDWARE_FLOW_CONTROL_DISABLE;
    hsd.Init.ClockDiv = 2;  // Adjust for eMMC speed

    if (HAL_SD_Init(&hsd) != HAL_OK) {
        Error_Handler();
    }
}

2. Mount the FATFS File System

#include "fatfs.h"

FATFS fs;  // File system object
FIL file;  // File object

void mount_emmc(void) {
    if (f_mount(&fs, "", 1) == FR_OK) {
        printf("eMMC mounted successfully!\n");
    } else {
        printf("Failed to mount eMMC.\n");
    }
}

3. Read and Write to eMMC

void write_file(void) {
    if (f_open(&file, "test.txt", FA_WRITE | FA_CREATE_ALWAYS) == FR_OK) {
        f_write(&file, "Hello eMMC!", 11, NULL);
        f_close(&file);
    }
}

void read_file(void) {
    char buffer[20];
    if (f_open(&file, "test.txt", FA_READ) == FR_OK) {
        f_read(&file, buffer, sizeof(buffer), NULL);
        f_close(&file);
        printf("Read Data: %s\n", buffer);
    }
}

3. Debugging and Testing

• Check SDIO clock using an oscilloscope.
• Use printf() debugging via UART.
• Ensure proper pull-up resistors on CMD and DAT lines.

Alternative Approach: Using SPI (Slower)

If SDIO is unavailable, you can use SPI (Single-bit mode). This is not recommended due to slow speed.

Pin of eMMC	Pin of STM32 SPI
CLK	SPI_SCK (PA5)
CMD (MOSI)	SPI_MOSI (PA7)
DAT0 (MISO)	SPI_MISO (PA6)
DAT3 (CS)	GPIO (e.g., PB6)

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Frequently Asked Questions (FAQ) on I²C Communication

1. What is I²C and how does it work? I²C (Inter-Integrated Circuit) is a serial communication protocol that enables multiple devices to communicate over a shared two-wire interface. It follows a master-slave architecture, where the master initiates communication, and slaves respond based on their unique addresses. citeturn0search0

2. What are the roles of SDA and SCL in I²C communication?

• SDA (Serial Data Line): Transfers data between devices.
• SCL (Serial Clock Line): Provides synchronization for data transmission.

Both lines are open-drain and require pull-up resistors for proper operation. citeturn0search0

3. What are the standard speeds of I²C communication? I²C supports different speed modes:

• Standard Mode (SM): 100 kbps
• Fast Mode (FM): 400 kbps
• Fast Mode Plus (FM+): 1 Mbps
• High-Speed Mode (HS): 3.4 Mbps
• Ultra-Fast Mode (UF): 5 Mbps

4. How many devices can be connected to a single I²C bus? I²C supports up to 127 devices (7-bit addressing) or 1024 devices (10-bit addressing). The actual number depends on bus capacitance and pull-up resistor values.

5. What is the difference between I²C and SPI?

Feature	I²C	SPI
Wires Needed	2 (SDA, SCL)	4 (MISO, MOSI, SCLK, SS)
Speed	Up to 3.4 Mbps	Up to 100 Mbps
Multi-Master Support	Yes	No
Complexity	Low	Higher

6. Why are pull-up resistors needed in I²C? Since I²C uses open-drain logic, pull-up resistors are required to keep the SDA and SCL lines HIGH when no device is actively pulling them LOW. citeturn0search0

7. What are ACK and NACK in I²C?

• ACK (Acknowledge): Slave pulls SDA LOW to confirm data reception.
• NACK (Not Acknowledge): Slave releases SDA HIGH, indicating an issue.

8. What is clock stretching in I²C? Clock stretching allows a slave device to hold SCL LOW to delay communication when it is not ready to process data. citeturn0search0

9. What happens if two devices on the I²C bus share the same address? This can cause bus conflicts. Solutions include:

• Using address-selectable devices
• Implementing an I²C multiplexer (e.g., PCA9548A)

10. How is bus arbitration handled in I²C? When multiple masters transmit at the same time, the master detecting a LOW while expecting HIGH loses arbitration and stops transmitting. citeturn0search0

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