Just use the datasheet, ch 16: Supply Controller.
This is a fine tunable beast of a Reset Controller. Question is: what is causing the behavior?
Could anyone with the problem scope clock generation, 3,3V vs. core voltage?
My Problem is only remotely related, sorry, following story:
I had, on some poor chinese saintsmard red due, the problem that no Reset would occur when uploading, so I had to press reset button at just the right time. Since I want to do Arduino and robotics with kids, and they will (hopefully) be using matlab/simulink target library (Matlab Coder is underlying technology, free in student version for Arduino, NXT/EV3 Lego Mindstorms, and Raspberry Pi) to let Matlab do the programming, this is not the way to go
I measured the reset signal that the ATmega16u2 gives out on Pin18 via R18 to master_reset.
This Resistor is given with a value of 1kOhm for the schematics from arduino.cc .
I found some residues of the soldering process between ISP headers on backside to via of Reset line. Perhaps this was enough to make the thing refuse to reset?
Now I attach a foto of my scope picture of the double reset into boot loader.
I will try to capture one with the new 1k Ohm resistor soldered on top of the old (10k) one.
I used my old Weller WECP-20 soldering station, freshly repaired, with the pointiest tip I could find.
Still I wish I could steady my hand with some glue or tape
Soldering paste was of help, but I always fear I spill it around, and it would creep under the ICs etc…
I put some pL with a needle tip on the contacts of the old resistor, then held the new one in place and heated up with soldering iron tip. Gave it one more tiniy bit of soldering paste, heated again…
Best thing would be heat radiation just for such a tiny spot. But well.
Then I measured the outcome directly on Pin22 of 16U2 to the Pin Header RESET.
This is ok for me