Add support for the JTAGICE3 programmer

This adds the configuration needed to support JTAGICE3. Note that
burning a bootloader doesn't work yet, due to bugs in avrdude. Uploading
sketches works as expected.

Author: matthijskooijman

hardware/arduino/avr/programmers.txt

@@ -75,3 +75,31 @@ stk500.protocol=stk500
 stk500.program.protocol=stk500
 stk500.program.tool=avrdude
 stk500.program.extra_params=-P{serial.port}
+
+# Note that until https://savannah.nongnu.org/bugs/?21954 and
+# https://savannah.nongnu.org/bugs/?42267 are fixed, burning a
+# bootloader does not work.
+# As a workaround, you can add -V to disable verification and modify
+# boards.txt to set all unused lock bits to 1 instead of 0.
+jtag3isp.name=Atmel JTAGICE3 (ISP mode)
+jtag3isp.communication=usb
+jtag3isp.protocol=jtag3isp
+jtag3isp.program.protocol=jtag3isp
+jtag3isp.program.tool=avrdude
+# Set a bitclock of 1us (the fastest supported value). This works for
+# microcontrollers running at 4Mhz and above.
+jtag3isp.program.extra_params=-B1
+
+# Note that until https://savannah.nongnu.org/bugs/?21954 is fixed,
+# burning a bootloader does not work.
+# As a workaround, you can modify boards.txt to set all unused lock bits
+# to 1 instead of 0.
+jtag3.name=Atmel JTAGICE3 (JTAG mode)
+jtag3.communication=usb
+jtag3.protocol=jtag3
+jtag3.program.protocol=jtag3
+jtag3.program.tool=avrdude
+# Set a bitclock of 0.1us (the fastest supported value). This should
+# work regardless of the crystal used, since JTAG doesn't use the MCU
+# clock but dictates its own clock.
+jtag3.program.extra_params=-B0.1