Allow avrdude to erase the chip before programming during ispload

We currently pass the -D (do not erase) option to avrdude
unconditionally in order to work around an Arduino Mega bootloader bug.
However, this has the side-effect of breaking the ispload target for all
non-XMEGA chips, since a write operation on these chips essentially ANDs
the new program with the existing memory contents. If the memory is not
first erased to contain only 0xff, the resulting image is garbage. This
patch makes it so we pass -D when we're using the Arduino bootloader but
don't pass it when we're using ISP directly.

Arduino.mk

@@ -1209,10 +1209,8 @@ endif
 # Default avrdude options
 # -V Do not verify
 # -q - suppress progress output
-# -D - Disable auto erase for flash memory
-# (-D is needed for Mega boards. See https://github.com/sudar/Arduino-Makefile/issues/114#issuecomment-25011005)
 ifndef AVRDUDE_OPTS
-    AVRDUDE_OPTS = -q -V -D
+    AVRDUDE_OPTS = -q -V
 endif
 
 AVRDUDE_COM_OPTS = $(AVRDUDE_OPTS) -p $(MCU)
@@ -1220,7 +1218,9 @@ ifdef AVRDUDE_CONF
     AVRDUDE_COM_OPTS += -C $(AVRDUDE_CONF)
 endif
 
-AVRDUDE_ARD_OPTS = -c $(AVRDUDE_ARD_PROGRAMMER) -b $(AVRDUDE_ARD_BAUDRATE) -P
+# -D - Disable auto erase for flash memory
+# (-D is needed for Mega boards. See https://github.com/sudar/Arduino-Makefile/issues/114#issuecomment-25011005)
+AVRDUDE_ARD_OPTS = -D -c $(AVRDUDE_ARD_PROGRAMMER) -b $(AVRDUDE_ARD_BAUDRATE) -P
 ifeq ($(CURRENT_OS), WINDOWS)
     # get_monitor_port checks to see if the monitor port exists, assuming it is
     # a file. In Windows, avrdude needs the port in the format 'com1' which is

HISTORY.md

@@ -32,6 +32,7 @@ I tried to give credit whenever possible. If I have missed anyone, kindly add it
 - Fix: Add "avrispmkii" to the list of isp that don't have a port. (Issue #279). (https://github.com/sej7278)
 - Fix: Make CXX compile .cpp files instead of CC. (Issue #285). (https://github.com/sej7278)
 - Fix: Changed IDE download URL *again* for Travis-CI. (https://github.com/sej7278)
+- Fix: Allow avrdude to erase the chip before programming during ispload (https://github.com/tchebb)
 
 ### 1.3.4 (2014-07-12)
 - Tweak: Allow spaces in "Serial.begin (....)". (Issue #190) (https://github.com/pdav)

arduino-mk-vars.md

@@ -1195,7 +1195,7 @@ AVRDUDE_ISP_BAUDRATE = 19200
 
 Options to pass to `avrdude`.
 
-Defaults to `-q -V -D` (quiet, don't verify, don't auto-erase). User values are not *ANDed* to the defaults, you have to set each option you require.
+Defaults to `-q -V` (quiet, don't verify). User values are not *ANDed* to the defaults, you have to set each option you require.
 
 **Example:**