Option to disable -e for bossac?

[fionawhim]

I’m using bobbin with an Adafruit PyPortal, and every time I flash I get a "SAM-BA operation failed" error.

I compared how bobbin calls bossac with how the Arduino IDE does it, and bobbin has an -e flag for erasing that Arduino doesn’t have.

When I remove the -e from bobbin, I can flash the PyPortal without issue.

Should this be an option that’s available? Would we want to default to still erasing but be able to set "--no-erase" or "erase = false" somewhere?

With some guidance on how you’d like it configured I could make the PR.

[jcsoo]

I haven't tried this recently, but I think the "-e" option makes the load process faster since it can do a bulk erase first rather than on a block-by-block basis? And maybe the PyPortal firmware simply doesn't support the bulk erase command?

I think for now a "--no-erase" option and "erase=false" loader option would make sense, keeping the behavior the same for existing users. A PR would be welcome!