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    <p>Im not sure why you need to have the capability to write to flash in your bootloader. Our bootloader does, because it can update the application program via serial port. So we eliminate the potential for inadvertent writes by ensuring that the loader does not contain any of the code that writes to flash. That code is downloaded is a header in the same package that contains the image to be written. The onboard image has the checksum of the programming algo stored, and verifies it before running it. </p> <p>If you are writing things that are generated internally, then I would look at hardware related interlocks. Only allow writes if you have previously set a particular discrete output pin to ON. To answer the problem of "what if the IP jumps past the checks"? you can do it in 2 parts. First set some critical variables for the algorithm. (the address to write to for example- keep that initialized to invalid memory, and only set it correctly in a separate call made before the write. Then have the write function check your HW interlock. Do one of the enable steps in an interrupt, or in response to a timer, something that is unlikely to be hit in the correct sequence if you have a rogue IP. </p> <p>If your IP can really jump anywhere , it may be impossible to prevent an inadvertent write. The best you can hope for is that you ensure the only path to get there also sets up everything else needed for a successful write. </p>
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    1. POAvoiding accidental firmware overwrite
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      1. VTUpMod
    1. COI'm doing the same thing (update via UART). There is write code in application and in bootloader. So they can cross-update each other, and I also store some configuration in flash. I don't know what uC you have, but the one I have cannot execute code from RAM, so uploading a code for writing is not an option. Actually I am using similar procedure as you described with HW interlock. This is what I tried to explain when I set the question... looks like I did a bad job :)
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      1. USStefan
    2. CO@Stefan: be careful with updating your bootloader from your application. What happens on power loss between the erase and write? Oops, your bootloader is gone and you've bricked your device. One a Freescale HCS08 project, the bootloader actually sets CPU registers to protect it from being overwritten, and it's impossible for the application to write to those pages in the flash. Be safe.
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      1. UStomlogic
    3. CO@tomlogic: I have 2 write codes - in aplication and in bootloader - and they can cross update each other. uC by default wakes into application code. If I fail to update the bootloader I still wake into application and can retry. And the bootloader uses a trick. It writes the application code from the highest page to the lowest. Before it writes the first (which is actually the highest) page, it writes 'jump to bootloader' into the page 0. Now the only concern is that it should not fail to write the very last page (page 0). So chances are extremely small to end up with non-recoverable flash.
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