see adafruit#37

Author: ladyada

boards.txt

@@ -14,6 +14,7 @@
 # License along with this library; if not, write to the Free Software
 # Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 
+menu.cache=Cache
 
 adafruit_feather_m0.name=Adafruit Feather M0
 adafruit_feather_m0.vid.0=0x239A
@@ -301,6 +302,11 @@ adafruit_metro_m4.build.pid=0x8020
 adafruit_metro_m4.bootloader.tool=openocd
 adafruit_metro_m4.bootloader.file=metroM4/bootloader.bin
 adafruit_metro_m4.compiler.arm.cmsis.ldflags="-L{build.variant.path}" -larm_cortexM4lf_math -mfloat-abi=hard -mfpu=fpv4-sp-d16
+adafruit_metro_m4.menu.cache.on=Enabled
+adafruit_metro_m4.menu.cache.on.build.cache_flags=-DENABLE_CACHE
+adafruit_metro_m4.menu.cache.off=Disabled
+adafruit_metro_m4.menu.cache.off.build.cache_flags=
+
 
 # Adafruit Feather M4 (SAMD51)
 # ------------------------------

cores/arduino/startup.c

@@ -224,7 +224,6 @@ void SystemInit( void )
   * Set up main clock
   */
 
-
 	GCLK->GENCTRL[GENERIC_CLOCK_GENERATOR_MAIN].reg = GCLK_GENCTRL_SRC(MAIN_CLOCK_SOURCE) |
 					GCLK_GENCTRL_IDC |
 					//GCLK_GENCTRL_OE |
@@ -241,6 +240,14 @@ void SystemInit( void )
   /* Use the LDO regulator by default */
   SUPC->VREG.bit.SEL = 0; 
 
+
+  /* If desired, enable cache! */
+#if defined(ENABLE_CACHE)
+  __disable_irq();
+  CMCC->CTRL.reg = 1;
+  __enable_irq();
+#endif
+
 //*************** END SAMD51 *************************//
 
 #else

platform.txt

@@ -54,6 +54,7 @@ compiler.readelf.cmd=arm-none-eabi-readelf
 
 # this can be overriden in boards.txt
 build.extra_flags=
+build.cache_flags=
 
 # These can be overridden in platform.local.txt
 compiler.c.extra_flags=
@@ -79,13 +80,13 @@ build.usb_manufacturer="Unknown"
 # ----------------
 
 ## Compile c files
-recipe.c.o.pattern="{compiler.path}{compiler.c.cmd}" {compiler.c.flags} -DF_CPU={build.f_cpu} -DARDUINO={runtime.ide.version} -DARDUINO_{build.board} -DARDUINO_ARCH_{build.arch} {compiler.c.extra_flags} {build.extra_flags} {compiler.arm.cmsis.c.flags} {includes} "{source_file}" -o "{object_file}"
+recipe.c.o.pattern="{compiler.path}{compiler.c.cmd}" {compiler.c.flags} -DF_CPU={build.f_cpu} -DARDUINO={runtime.ide.version} -DARDUINO_{build.board} -DARDUINO_ARCH_{build.arch} {compiler.c.extra_flags} {build.extra_flags} {build.cache_flags} {compiler.arm.cmsis.c.flags} {includes} "{source_file}" -o "{object_file}"
 
 ## Compile c++ files
-recipe.cpp.o.pattern="{compiler.path}{compiler.cpp.cmd}" {compiler.cpp.flags} -DF_CPU={build.f_cpu} -DARDUINO={runtime.ide.version} -DARDUINO_{build.board} -DARDUINO_ARCH_{build.arch} {compiler.cpp.extra_flags} {build.extra_flags} {compiler.arm.cmsis.c.flags} {includes} "{source_file}" -o "{object_file}"
+recipe.cpp.o.pattern="{compiler.path}{compiler.cpp.cmd}" {compiler.cpp.flags} -DF_CPU={build.f_cpu} -DARDUINO={runtime.ide.version} -DARDUINO_{build.board} -DARDUINO_ARCH_{build.arch} {compiler.cpp.extra_flags} {build.extra_flags} {build.cache_flags} {compiler.arm.cmsis.c.flags} {includes} "{source_file}" -o "{object_file}"
 
 ## Compile S files
-recipe.S.o.pattern="{compiler.path}{compiler.S.cmd}" {compiler.S.flags} -DF_CPU={build.f_cpu} -DARDUINO={runtime.ide.version} -DARDUINO_{build.board} -DARDUINO_ARCH_{build.arch} {compiler.S.extra_flags} {build.extra_flags} {compiler.arm.cmsis.c.flags} {includes} "{source_file}" -o "{object_file}"
+recipe.S.o.pattern="{compiler.path}{compiler.S.cmd}" {compiler.S.flags} -DF_CPU={build.f_cpu} -DARDUINO={runtime.ide.version} -DARDUINO_{build.board} -DARDUINO_ARCH_{build.arch} {compiler.S.extra_flags} {build.extra_flags} {build.cache_flags} {compiler.arm.cmsis.c.flags} {includes} "{source_file}" -o "{object_file}"
 
 ## Create archives
 # archive_file_path is needed for backwards compatibility with IDE 1.6.5 or older, IDE 1.6.6 or newer overrides this value