When building custom firmware (Yocto, Buildroot), decoding the CID helps identify which eMMC chip is present on the target board, ensuring the correct device tree and driver settings.
Most CID decoders are either small software utilities or web-based scripts. They work by taking a 32-character hexadecimal string and using bitwise shifts and masks to isolate the specific bits assigned to each field. For example, to find the , a decoder looks at bits [15:8] of the register, where 4 bits represent the month and 4 bits represent the year (offset from 2010 or 1997 depending on the specification version). Conclusion
su cat /sys/block/mmcblk0/device/cid
Ensures that batches of IoT devices use the exact components specified in the Bill of Materials (BOM). Implementation Requirements
Helps technicians identify if a specific eMMC revision is prone to known bugs (e.g., "eMMC sudden death") and requires a firmware update.
When decoding a CID, the first two characters (the first byte) indicate the manufacturer. Below are common hex identifiers found during decoding: Manufacturer 0x02 SanDisk / Western Digital 0x11 Toshiba / Kioxia 0x13 0x15 0x45 0x70 0x90 0xfe
: Assigned by JEDEC (e.g., 0x15 for Samsung, 0x13 for Micron). Device/BGA
1501004D34474255015A1AC0E80100 Byte‑wise (MSB first):
The is a read-only 16-byte (128-bit) configuration memory space populated by the semiconductor manufacturer during production. It acts as a digital birth certificate for the chip, verifying its origin, authenticity, and physical properties. Structure of a 128-Bit eMMC CID Register
The CID is a 16-byte (128-bit) unique identifier hardcoded into the eMMC's internal register. Unlike standard storage data, the CID is generally read-only and serves as the "fingerprint" of the chip. It contains technical metadata required for device authentication, firmware debugging, and hardware identification. Key Fields in the CID Structure
For privacy or batch processing, write a simple Python decoder.
The month and year the chip left the factory. Why Use an eMMC CID Decoder?
Every eMMC device contains a , a 16-byte (128-bit) read-only register that is programmed during the manufacturing process. Unlike the user data stored on the chip, the CID is permanent and unique to that specific hardware unit. It serves as the "fingerprint" of the storage device, essential for system bootloaders, kernels, and forensic analysts to identify the exact hardware they are interacting with. Anatomy of an eMMC CID