[avrdude-dev] [bug #30061] stk500 skips writing blocks of 0xff, even if the part/page wasn't erased

[anonymous]

URL:
  <http://savannah.nongnu.org/bugs/?30061>

                 Summary: stk500 skips writing blocks of 0xff, even if the
part/page wasn't erased
                 Project: AVR Downloader/UploaDEr
            Submitted by: None
            Submitted on: Mon 07 Jun 2010 03:36:06 AM UTC
                Category: None
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: None
                  Status: None
                 Privacy: Public
             Assigned to: None
         Originator Name: Adam Wolf
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any

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Details:

I noticed that when writing many blocks of 0xff to an atmega328p (with
auto-erase off), sometimes a big stretch didn't actually write, and the values
were preserved from the last program.

I noticed if I changed even one bit in the area to a 0, the block would
actually write.

I tracked it down-- in stk500_paged_write in stk500.c, there's a check for
stk500_is_page_empty.  If the whole page consists of 0xFF, the page isn't
written.

To me, to do this correctly, you'd have to take into account if the page was
actually set to all 0xff.  I tested it by commenting out the entire 

    /* Only skip on empty page if programming flash. */
    if (flash) {
      if (stk500_is_page_empty(addr, block_size, m->buf)) {
          continue;
      }
    }


section.

Making this change fixed my issue.

Is this intended behavior, and just part of what disabling auto-erase means?

I was thinking a more optimal fix might be to skip writing blank pages if you
know the page has been erased, but I wasn't quite sure of how you folks would
want that implemented.




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