As embedded applications become more and more widespread, product security becomes more and more important. On the one hand, it is to protect the hardware design, and on the other hand, it is also for the safety of the product itself to prevent it from being HACKED.
In embedded systems, all codes and system data are stored inside the FLASH chip. The characteristic of FLASH chip is that it can be erased and written multiple times, and the data will not be lost when power is turned off. In order to protect the data in FLASH, more and more FLASH manufacturers provide a special register inside FLASH: the OTP register. OTP=ONE TIME PROGRAMDABLE, which means that this register can only be programmed once, and it can no longer be modified after programming. The 0TP register is very similar to the FLASH data area. 1 can be rewritten as 0, but 0 can never be written as 1. If there is a 32-bit OTP register, the value produced is OxFFFFFFFF. If the user writes the value of the OTP register through programming After it is OxFFFFFFFE, the OTP register can no longer be rewritten to 0xFFFFFFFF; of course, the value of this OTP register can also be rewritten to 0xFFFFFFFD or others.
In order to provide protection for the 0TP register, this type of FLASH chip generally also provides a LOCK register. The LOCK register is also ONE TIME PROGRAMMABLE. Each bit of the LOCK register corresponds to an OTP register. If the bit (BIT) of the LOCK register corresponding to the OTP register is written from 1 to 0, it means that the locked OTP register cannot be written anymore. Even if the current value of OTP is 0XFFFFFFFF, its value will never be changed. can be rewritten.
Through the OTP register and LOCK register, users can save some specific information in 0TP, such as software version number, hardware version number, secret key and other information. At the same time, there will be another OTP register inside this type of FLASH chip. This register has been programmed by the manufacturer when it is produced, written with a specific serial number, and locked. If necessary, FLASH manufacturers can also write specific serial numbers according to customer needs. In this way, each chip will have a different ID number to avoid being copied.
In addition to FLASH chips, many CPU manufacturers also provide similar OTP registers inside the CPU for users to use, which is conducive to the development of safer applications. Like some larger manufacturers, such as TI, FREESCALE, etc., they often do not disclose the data sheets of certain chips. If you want to obtain their data sheets, you must place a large order and sign a certain confidentiality agreement.
OTP itself does not provide absolutely secure applications. However, the provision of 0TP helps developers develop and deploy more secure applications and protect their own and customers’ interests. Many large manufacturers, such as NOKIA, MOTOROAL, SAMSUNG and SONYERRICSON, need to develop some mobile phones that can only be used in their own networks according to the requirements of customers (operators). Many software and hardware protections are based on OTP.
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