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stm32microcontroller

OTP size for STM32F746XX

I found a strange mismatch in the reference manual for the OTP memory size: Accordingly to the manual (RM0385, page 78) the start-address of the OTP memory begins at 0x1FF0 F000 and ends at address: 0x1FF0 F41F (in AXIM mode) and is declared as a memory area with the size of 1024 bytes:

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But if I calculate 0x1FF0F41F - 0x1FF0F000 + 1 I get a total of 1056 bytes OTP memory?!

Same addresses are set in the latest CMSIS header V1.17.0 (https://raw.githubusercontent.com/STMicroelectronics/STM32CubeF7/master/Drivers/CMSIS/Device/ST/STM32F7xx/Include/stm32f746xx.h):

  • #define FLASH_OTP_BASE 0x1FF0F000UL
  • #define FLASH_OTP_END 0x1FF0F41FUL

Is this a typo in the manual or is my calculation wrong?

Solution

  • I don't think it's a typo, and your calculation is correct. My explanation is as follows:

    Chapter 3.6 of the same Reference Manual shows the organization of the one-time programmable (OTP) part of the OTP area, and explains:

    The OTP area is divided into 16 OTP data blocks of 64 bytes and one lock OTP block of 16 bytes. The OTP data and lock blocks cannot be erased. The lock block contains 16 bytes LOCKBi (0 ≤ i ≤ 15) to lock the corresponding OTP data block (blocks 0 to 15). (...)

    So it consists of 1024 data bytes and 16 lock bytes. I guess the lock bytes are implemented as special "registers" and are not considered part of the sector. It's more a matter of definition and does not really matter that much. There probably is a 1024-byte sector to write the (one-time programmable) data to, but the address range is slightly larger because the lock bits have to be addressed as well.