Electronic – Run code once in lifetime of an embedded C program

cembeddedmicrocontroller

How can I make a code snippet run only once in the lifetime of a program? It can be turned off and turned on many times. The only option to run the code snippet again must be flashing the board again.

The code is a Calibration Section which I don't want to run again. If I use EEPROM or Flash we will be setting a Flag to true or False. So When we first read that memory location what would be the random value in that memory area?

What is the best method to implement this in embedded C?

Best Answer

Your microcontroller might have some EEPROM, OTP memory, user fuse bits, where you can set a flag.

There is no "best method in embedded C", writing nonvolatile memory is different in every microcontroller.

edit:

FLASH

Flash memory contents are erased while programming the device. After programming, all bytes that weren't written contain 0xFF. Consult the datasheet to find an area that can be safely programmed from within the running firmware.

EEPROM

Although it's not guaranteed in the datasheets, all EEPROMs I've seen so far contained 0xFF:s when shipped from the factory (except ones preprogrammed with an unique MAC address, but that's explicitly documented). Some programming devices/software are able to erase or program EEPROM contents too. Some can be write protected, permanently or reversibly.

OTP

One Time Programmable memory always contains well defined initial values, documented in the datasheet.

It's always a good idea to include a good checksum like CRC32 with the data written, to protect against data corruption caused by defective parts, transmission errors, cosmic rays, whatever.

Related Solutions

Electronic – Automating linker file change

In don't know your linker, but the gcc linker can PROVIDE a label, which address can be used in the code. This feature is commonly used to inform the startupcode about the start and end of the DATA and BSS segments, so the BSS can be cleared and the DATA (in RAM) can be intialized from is copy in ROM.

Fragment from an (LPC1343) linkerscript I use:

.text :
{
    . = ALIGN(4);
    __text_start = .;
    PROVIDE(__text_start = __text_start);

            // all text segments are listed here

    . = ALIGN(4);
    __text_end = .;
    PROVIDE(__text_end = __text_end);
} > rom

The label __text_end will be at the address beyond the text. It can be used in the code for the CRC calculation.

Two remarks:

You say you check the code segment. Do you check the DATA segment (initialised global values) too?
If this task was put onto me I would consider to arrange things that the unused flash locations are filled with a known value, and arrange the checksumn over the total flash.

PIC24E writing address and increment for ICSP programming

You'd start at 0x0, because the stuff there (IVT, etc) are part of what you want to upload. PIC addressing is always confusing because of their insistence on weird architectures with 14 or 24 bit words, but I believe the destination address would increment by 0x100 for 128 instructions -- this is supported by the comment in 5.2.9 of the programming spec, "The destination address should be a multiple of 0x100", as well as the flow chart shown in figure 3-4.

Best Answer

Related Solutions

Electronic – Automating linker file change

PIC24E writing address and increment for ICSP programming

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