fix samd21 race condition with setup packet

reproduced with Adafruit_TinyUSB_ArduinoCore port commit 11d669b4d2a40eb2fc5e51b2a9707a6de9d42363 and SAMD BSP 1.6.1

examples/make.mk

@@ -46,31 +46,32 @@ SRC_C += $(subst $(TOP)/,,$(wildcard $(TOP)/hw/bsp/$(BOARD)/*.c))
 
 # Compiler Flags
 CFLAGS += \
-	-fdata-sections \
-	-ffunction-sections \
-	-fsingle-precision-constant \
-	-fno-strict-aliasing \
-	-Wdouble-promotion \
-	-Wstrict-prototypes \
-	-Wall \
-	-Wextra \
-	-Werror \
-	-Wfatal-errors \
-	-Werror-implicit-function-declaration \
-	-Wfloat-equal \
-	-Wundef \
-	-Wshadow \
-	-Wwrite-strings \
-	-Wsign-compare \
-	-Wmissing-format-attribute \
-	-Wunreachable-code \
-	-Wcast-align
-	
+  -ggdb \
+  -fdata-sections \
+  -ffunction-sections \
+  -fsingle-precision-constant \
+  -fno-strict-aliasing \
+  -Wdouble-promotion \
+  -Wstrict-prototypes \
+  -Wall \
+  -Wextra \
+  -Werror \
+  -Wfatal-errors \
+  -Werror-implicit-function-declaration \
+  -Wfloat-equal \
+  -Wundef \
+  -Wshadow \
+  -Wwrite-strings \
+  -Wsign-compare \
+  -Wmissing-format-attribute \
+  -Wunreachable-code \
+  -Wcast-align
+
 # Debugging/Optimization
 ifeq ($(DEBUG), 1)
-  CFLAGS += -Og -ggdb
+  CFLAGS += -Og
 else
-	CFLAGS += -Os
+  CFLAGS += -Os
 endif
 
 # Log level is mapped to TUSB DEBUG option
@@ -80,14 +81,11 @@ endif
 
 # Logger: default is uart, can be set to rtt or swo
 ifeq ($(LOGGER),rtt)
-	RTT_SRC = lib/SEGGER_RTT
-	
-	CFLAGS += -DLOGGER_RTT -DSEGGER_RTT_MODE_DEFAULT=SEGGER_RTT_MODE_BLOCK_IF_FIFO_FULL
+  RTT_SRC = lib/SEGGER_RTT
+  CFLAGS += -DLOGGER_RTT -DSEGGER_RTT_MODE_DEFAULT=SEGGER_RTT_MODE_BLOCK_IF_FIFO_FULL
   INC   += $(TOP)/$(RTT_SRC)/RTT
   SRC_C += $(RTT_SRC)/RTT/SEGGER_RTT_printf.c
   SRC_C += $(RTT_SRC)/RTT/SEGGER_RTT.c
-  
 else ifeq ($(LOGGER),swo)
-	CFLAGS += -DLOGGER_SWO
-
+  CFLAGS += -DLOGGER_SWO
 endif

hw/bsp/feather_m0_express/board.mk

@@ -41,5 +41,11 @@ FREERTOS_PORT = ARM_CM0
 JLINK_DEVICE = ATSAMD21G18
 JLINK_IF = swd
 
-# flash using jlink
-flash: flash-jlink
+# flash using bossac at least version 1.8
+# can be found in arduino15/packages/arduino/tools/bossac/
+# Add it to your PATH or change BOSSAC variable to match your installation
+BOSSAC = bossac
+
+flash: $(BUILD)/$(BOARD)-firmware.bin
+	@:$(call check_defined, SERIAL, example: SERIAL=/dev/ttyACM0)
+	$(BOSSAC) --port=$(SERIAL) -U -i --offset=0x2000 -e -w $^ -R

hw/bsp/feather_m4_express/board.mk

@@ -44,5 +44,11 @@ FREERTOS_PORT = ARM_CM4F
 JLINK_DEVICE = ATSAMD51J19
 JLINK_IF = swd
 
-# flash using jlink
-flash: flash-jlink
+# flash using bossac at least version 1.8
+# can be found in arduino15/packages/arduino/tools/bossac/
+# Add it to your PATH or change BOSSAC variable to match your installation
+BOSSAC = bossac
+
+flash: $(BUILD)/$(BOARD)-firmware.bin
+	@:$(call check_defined, SERIAL, example: SERIAL=/dev/ttyACM0)
+	$(BOSSAC) --port=$(SERIAL) -U -i --offset=0x4000 -e -w $^ -R

hw/bsp/itsybitsy_m0/board.mk

@@ -41,5 +41,11 @@ FREERTOS_PORT = ARM_CM0
 JLINK_DEVICE = ATSAMD21G18
 JLINK_IF = swd
 
-# flash using jlink
-flash: flash-jlink
+# flash using bossac at least version 1.8
+# can be found in arduino15/packages/arduino/tools/bossac/
+# Add it to your PATH or change BOSSAC variable to match your installation
+BOSSAC = bossac
+
+flash: $(BUILD)/$(BOARD)-firmware.bin
+	@:$(call check_defined, SERIAL, example: SERIAL=/dev/ttyACM0)
+	$(BOSSAC) --port=$(SERIAL) -U -i --offset=0x2000 -e -w $^ -R

hw/bsp/itsybitsy_m4/board.mk

@@ -44,5 +44,11 @@ FREERTOS_PORT = ARM_CM4F
 JLINK_DEVICE = ATSAMD51J19
 JLINK_IF = swd
 
-# flash using jlink
-flash: flash-jlink
+# flash using bossac at least version 1.8
+# can be found in arduino15/packages/arduino/tools/bossac/
+# Add it to your PATH or change BOSSAC variable to match your installation
+BOSSAC = bossac
+
+flash: $(BUILD)/$(BOARD)-firmware.bin
+	@:$(call check_defined, SERIAL, example: SERIAL=/dev/ttyACM0)
+	$(BOSSAC) --port=$(SERIAL) -U -i --offset=0x4000 -e -w $^ -R

hw/bsp/metro_m0_express/board.mk

@@ -41,5 +41,11 @@ FREERTOS_PORT = ARM_CM0
 JLINK_DEVICE = ATSAMD21G18
 JLINK_IF = swd
 
-# flash using jlink
-flash: flash-jlink
+# flash using bossac at least version 1.8
+# can be found in arduino15/packages/arduino/tools/bossac/
+# Add it to your PATH or change BOSSAC variable to match your installation
+BOSSAC = bossac
+
+flash: $(BUILD)/$(BOARD)-firmware.bin
+	@:$(call check_defined, SERIAL, example: SERIAL=/dev/ttyACM0)
+	$(BOSSAC) --port=$(SERIAL) -U -i --offset=0x2000 -e -w $^ -R

hw/bsp/metro_m4_express/board.mk

@@ -44,5 +44,11 @@ FREERTOS_PORT = ARM_CM4F
 JLINK_DEVICE = ATSAMD51J19
 JLINK_IF = swd
 
-# flash using jlink
-flash: flash-jlink
+# flash using bossac at least version 1.8
+# can be found in arduino15/packages/arduino/tools/bossac/
+# Add it to your PATH or change BOSSAC variable to match your installation
+BOSSAC = bossac
+
+flash: $(BUILD)/$(BOARD)-firmware.bin
+	@:$(call check_defined, SERIAL, example: SERIAL=/dev/ttyACM0)
+	$(BOSSAC) --port=$(SERIAL) -U -i --offset=0x4000 -e -w $^ -R

src/portable/microchip/samd/dcd_samd.c

@@ -43,6 +43,8 @@ static inline void prepare_setup(void)
 {
   // Only make sure the EP0 OUT buffer is ready
   sram_registers[0][0].ADDR.reg = (uint32_t) _setup_packet;
+  sram_registers[0][0].PCKSIZE.bit.MULTI_PACKET_SIZE = sizeof(_setup_packet);
+  sram_registers[0][0].PCKSIZE.bit.BYTE_COUNT = 0;
 }
 
 // Setup the control endpoint 0.