Saving password data to flash

future · Joined: 14 May 2004 Posts: 330

Hi,

I am starting to implement a security scheme to a previous project and thinking about a 4 or 6 digit password to unlock functions.

The internal eeprom is already full, so some bytes of flash will be used.

What method you advise me to use? #org and write flash, label_adress, other way?

I am not willing to write all possibilities and try them as I am used to do because I don't have much time.

Thank you.

Ttelmah · Guest

The normal method is to use #ROM, which does most of the work for you. So if (for instance), you have something like:

ckielstra · Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands

I've found the #ROM statement in the 16-bit parts (PIC18) to be a bit confusing. You have the following options:

// Example to set words:
#ROM 0xF00000 = {1, 2, 3, 4, 5}

// Example to set bytes:
#ROM int8 0xF00000 = {1, 2, 3, 4, 5}

// Example to set a string of bytes:
#ROM 0xF00010 = {"12345"}

future · Joined: 14 May 2004 Posts: 330

Great! The solution looks simple.

But, how should I do to let the compiler choose an empty address?

The last 100 words of flash is being used by the tiny bootloader and the first 10k bytes by the firmware.

Something like the first page after the end of the firmware may be fine.

If this address is at the start of the page, the erase before write will be handled by the compiler, one thing less to worry.