[avrdude-dev] [bug #53839] ATtiny and Programmer running after download done

[Michael Sadaway]

Follow-up Comment #3, bug #53839 (project avrdude):

There are still applications in which chips are programmed separately outside
the devices in which they are eventually installed. After all, some AVR chips
are still sold in DIPs to facilitate this.

However, even if you discount this case and even if you are O.K. with letting
the newly programmed chip run immediately after programming it, there is still
johnbarr's "bug #2" to consider.

For chips with a limited number of pins, i.e., the ATtiny84 and 85, the same
pins used for programming the chips are often also used as I/O pins in the
application.

We have noticed that if the code downloaded to the chip runs and outputs
signals to either the MISO or MOSI pin, AVRDUDE apparently responds by
generating signals on the SCK pin.

If the SCK pin is used as an input pin in the application, this can have
undesirable effects.

In johnbarr's case, the SCK pin is also used as an input from a switch, and
the SCK signals generated by AVRDUDE after the chip is programmed activate the
switch input and cause his code to modify EEPROM.

In another application, the unwanted SCK signals could have a different
undesirable effect.

It would be better if AVRDUDE didn't send any signals to a chip once it has
been programmed.


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