With all of the fuss and bother involved in swapping jumpers and rebooting, I had forgotten that one of the first things that I accomplished by following the Gertduino setup instructions (both the instructions in the Gertduino manual and on the Friends of the Unicorn site) was to install the Arduino IDE. The key to doing that is following the link to a more complete set of instructions at https://projects.drogon.net/raspberry-pi/gertboard/arduino-ide-installation-isp/
There is another page of helpful tips on actually using the Arduino IDE once it has been installed (it's written for the Gertboard, but using the Gertduino should be similar) at https://projects.drogon.net/raspberry-pi/gertboard/using-the-arduino-ide/
I'm pretty sure that I followed those instructions to the letter, yet I'm not quite sure where to find the IDE. But upon issuing the startx command to bring up the Pi's desktop and mousing over the menu icon at the lower left of the screen, I noticed that a new "Electronics" category had been added to the menu, and the lone menu choice in that category is "Arduino IDE". Sure enough, clicking on that menu (and waiting like forever) brings up a familiar green IDE window.
By default, the bottom right corner of the IDE says Arduino Uno on COM1. Neither the Uno part nor the COM1 part of the default setting is correct, but that should be easy enough to change.
On the menu, I select: Tools -> Board -> Gertuino with ATmega328 (GPIO)
Yes, the menu actually says "Gertuino" instead of "Gertduino", but I can't complain too much, because after all it's free, and I understand what it's trying to say even if it hasn't quite gotten it right.
So now the bottom right corner of the IDE says Gertuino with ATmega328 (GPIO) on COM1. That's progress, although the COM1 part is still wrong. But when in doubt, continue following the instructions.
Back to the menu. I select: Tools -> Programmer -> Raspberry Pi GPIO
The status message at the bottom of the IDE still says "COM1", but when I go back to the tools/programmer menu I see that "Raspberry Pi GPIO" is selected, so I'm willing to give it the benefit of the doubt.
The "Hello World" of the Arduino world is the venerable Blink example program (this is a different 'Blink' than the sequential LED blinker that I previously loaded into the Gertduino on the command line via the .hex file). If it works, then I should be good to go.
You know the routine: File -> Examples -> 01.Basics -> Blink
The source code loads into a new IDE window as expected. Let me see if I can compile it.
It's slow, but it works. Now to upload the program to the Gertduino. Instead of clicking on the Upload button I'm going to use: File -> Upload Using Programmer
The IDE appears to go through another compile (just as when using the normal Upload button), and this time the compile step runs pretty quickly. And, although it's missing the Uno's usual feedback of blinking Rx and Tx LEDs as the program is uploaded, LED D5 is now blinking on and off. In fact, much to my relief, it's turning on for a second and then off for a second. Up to this point I was still not sure whether my ATmega328P was running at 1 MHz or at 16 MHz, but my guess is that since the delay() call in the Blink program is working properly, the clock speed must be right. Is there any other way to confirm that? I'll have to give it some thought.
But at the moment there's something else that needs some attention. Prior to uploading the Blink example program the Gertduino was happily running the other Blink LED sequencer, and while I now have one of the LEDs (D5) blinking on and off instead of each LED blinking on and off in sequence, one of the other LEDs is stuck 'on' (D9). My guess is that D9 happened to be the last one that was set on by the earlier Blink program at the time when the new Blink was uploaded and launched. That behavior is certainly unexpected. When I first installed the Gertduino board onto the Pi, all of the LEDs were lit up (also unexpectedly). Now, other than the LED that my program is blinking and the one that is stuck on, the rest of the LEDs are off.
I would have expected that the ATmega328P would be automatically reset after uploading the code from the IDE, just as is done with the normal Arduino bootloader, which should have reset all of the microcontroller's output ports to their default, high-impedance state.
I'm going to press the Gertduino's reset button to see what happens. Hmmm. No change in the behavior of the LEDs. It's times like these when a Gertduino schematic would come in handy, but alas it's still among the missing.
But, as they say, Google is your friend. A quick search leads me to a version of the Gertduino manual that actually contains the previously AWOL schematic in Appendix A:
Now, that's what I call progress.