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I bought a SainSmart Arduino Mega 2560. I uploaded a small sketch to it, and it uploaded fine. When I upload a larger sketch though, I get this error:

verification error, first mismatch at byte 0x3895
         0xdf != 0x44

So obviously there's nothing wrong with my bootloader because I can upload smaller files. Why is this happening?

user3042719
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2 Answers2

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If your sketch contains !!! in it, that can cause some versions of the bootloader to drop into interactive mode, eg.

Serial.println ("Rocket firing!!!");

Also there can be problems with 0xFF bytes in your code causing the bootloader to incorrectly assume that that page of memory was erased, when it was not.

I have a bootloader-uploader sketch at: Atmega bootloader programmer

You need a second board to use it (eg. a Uno) - the bootloader for the Mega2560 is a reasonably up-to-date one. I haven't actually tested it with the Sainsmart version of the Mega, but I presume that internally that part is the same.

Nick Gammon
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I believe I have finally understood this error today, and would like someone to verify or refute.

In "avrdude.conf" there is defined for each processor and for each memory type a minimum duration and a maximum duration that the programmer will repeat trying to write each byte. These have values of "min_write_delay = 4500" and "max_write_delay = 4500" (no idea what the units are).

After increasing the max_write_delay to "max_write_delay = 16000" (arbitrary increase but keeping it less than a 16 bit signed integer to avoid buffer overflow risks), for all memory types (but I would presume that only "flash" memory needs the parameter to be altered) my Arduino takes an extra 30 seconds to program, but no more verification errors.

user23265
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