Auto-reset fix for Uno and Mega 2650

[giseburt]

This is a modification of the usbserial code for the 8u2 chip. The intent is to make auto-reset only work when programming, and remain backwards compatible with the software.

I added a check for an about 1 second delay between DTR toggles before the reset line is switched. This allows connection and reconnection from OS X and (untested) Linux without a reset.

Also optimized for size, since this check pushed the size over 4K. It might be a little faster as well.

I've also included HEX files for both UNO and Mega 2650, but I haven't tested the UNO files. (I don't have an UNO, sorry.) I did NOT include the combined HEX file that have the DFU programmer in them.

[damellis]

I'd like to keep the current behavior of the 8U2 firmware in this respect. That is, it should merely pass through the DTR state changes made by the operating system. I know the auto-reset on serial connection is annoying in some cases, but it's useful in others and also the established behavior.

[giseburt]

I tried very hard to remove only the unwanted resets, leaving the
established behavior that is expected. That was the real goal.

If someone wants to force a reset they still can with two DTR toggles
one second apart.

I believe that most projects are not expecting or wanting the whole
device to reset upon establishing a serial connection. They simply
have to deal with it now or physically alter the board to permanenty
remove that.

Thank you for listening,
-Rob

PS: I wrote a blog post that explains motivations:
http://www.tinkerin.gs/2011/03/arduino-auto-reset-software-fix.html

On Mar 29, 2011, at 9:15 AM, damellis
[email protected]
wrote:

I'd like to keep the current behavior of the 8U2 firmware in this respect. That is, it should merely pass through the DTR state changes made by the operating system. I know the auto-reset on serial connection is annoying in some cases, but it's useful in others and also the established behavior.

Reply to this email directly or view it on GitHub:
#22 (comment)

[andyross]

Could we get more discussion about this? Are there alternatives you'd consider? Is giseburt's "knocking" algorithm not acceptable for getting a reset done from the host?

While I accept that the reset behavior is there for legacy compatibility, I honestly consider it a bug. Plugging or unpluging a data cable really shouldn't be resetting the unit by design.

[NicoHood]

You wont break older board i think, but the really use of this is minimal. There are so many boards out there delivered with the old firmware, i think this wont help much. You still can do this for your board if you like to via DFU. Thats my opinion.