Here’s a second use of yesterday’s ISP plug: pre-loading ATmega’s with a fixed sketch and bootloader.

This uses a very nice trick from the Arduino Boot-Cloner: store the code to be sent to the target MPU as PROGMEM data inside the ISP sketch itself!

I’ve adapted that Boot Cloner so that it takes its data from a separate C include file, added a couple of other features, and speeded the whole thing up a bit.

The result is called “isp_prepare” (code here).

Here’s what you’ll see on the USB serial port when starting it up:

The list reports the files which have been integrated into this sketch at build time, using this C code at the top of isp_prepare.pde:

Here is the contents of that include file, with most of the data bytes omitted:

The data consists of “sections” of code, to be programmed into the target ATmega using ISP. In this case there are two sections, a RF12demo sketch starting at address zero, and a bootloader in high memory.

Here’s is isp_prepare in action:

So the steps to load RF12demo onto a JeeNode with a fresh ATmega are as follows:

• upload this isp_prepare.pde sketch to a “master” JeeNode
• insert the ISP plug described yesterday,
• connect the target JeeNode to this master JeeNode via ISP
• enter G to start programming and wait for it to complete
• done: disconnect, now the target JeeNode is ready to run with RF12demo on it

I’ve also included a “data_blink.h” header file, if you want to preload the ATmega with the standard Arduino blinking LED demo. Just change the include in isp_prepare and upload the sketch again.

I can now use this setup for initializing all the ATmega’s here at Jee Labs, since it means I no longer have to start up the Arduino IDE or use avrdude.

Convenience!