OTP User Guide

[中文]

Overview

OTP (One-Time Programmable Memory) is a type of non-volatile memory that can be written only once but read multiple times. It is widely used to store immutable data such as security configurations, unique identifiers, and factory calibration parameters.

Typical Features

Feature

Description

Write Once

Each bit is permanently locked after being written; cannot be erased or rewritten

Non-volatile

Data is retained after power-off

Bit-wise Programmable

Supports bit-wise programming; some chips support byte-wise programming

High Security

Suitable for storing encryption keys, chip ID, MAC address, and other sensitive information

Controlled Access

Can configure read-only regions, write protection, or access restrictions

OTP Characteristics

In the BK7258 chip, OTP is divided into two regions: OTP1 and OTP2. OTP1 is reserved for internal use by the company, containing Device ID, MAC address, Public key, and other reserved information. Only the OTP2 region is available for customer use, with an address range of [0x4B010600—-0x4B010C00], providing 1.5KB of space.

OTP2 Usage Layout

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OTP2 Side

OTP2 is a readable and programmable region. Addresses 0x000~0x2FF are divided into 767 small partitions. The address range is [0x4B010000—-0x4B010C00]. Each partition’s permissions can be modified by changing the LOCK OTP2 CELL: Read/Write -> Read-Only -> No Access.

Important

The first 1.5KB of the address space [0x4B010000—-0x4B010600] is reserved for BEKEN internal use and is not available to customers. The customer-accessible region is [0x4B010600—-0x4B010C00], providing 1.5KB of usable space.

Usage Notes

  • Data cannot be changed after writing; verify data carefully before writing.

  • It is recommended to use “emulation burn mode” for software verification first.

  • Writing operations typically require a certain delay (about 5-10ms programming time).

Using the OTP Driver

How to Add Custom Partition Information in OTP2

    1. To add a specific partition to OTP2 (taking BK7258 as an example), simply add a line in ap/middleware/boards/bk7258/csv/otp2.csv with columns [id, name, size, offset, end, privilege, security]. See example at the end of this document.

    1. The SDK tools will automatically generate the corresponding header files during compilation; no manual editing is required. The generated header is located at ../_build/_otp.c.

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    1. After configuring as above, you can use CLI commands for testing. Related test code can be found at ap/components/bk_cli/cli_otp.c (example command: otp_ahb read item size).

Note

Before writing to a region of OTP2, it is recommended to first read it to confirm whether it has already been used (default OTP value is 0).

Structure Array otp_ahb_map Configuration

    1. The otp_ahb_map structure is defined in ap/middleware/driver/otp/otp_driver.h.

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Note

  • name: The item_id of the access region; this ID is used to access the region later. The d_size field specifies the allocated size in bytes.

  • allocated_size: The allocated size in bytes.

  • offset: The offset relative to the base address.

  • privilege: The access permission of the region.

    1. The otp2_id_t enum stores the name fields; it is automatically generated at ../_build/_otp.h.

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Note

  • Example: configuring OTP_CUSTOMER_KEY2.

  • First, add a new id=6 entry in otp2.csv, incrementing the ID sequentially. Define the name field, e.g. OTP_CUSTOMER_KEY2.

  • Then, configure the size (e.g. 256 bytes).

  • The offset is equal to the end of the previous entry (hexadecimal).

  • Set privilege to OTP_READ_WRITE and security to FALSE.

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