fix samd21 race condition with setup packet

reproduced with Adafruit_TinyUSB_ArduinoCore port commit 11d669b4d2a40eb2fc5e51b2a9707a6de9d42363 and SAMD BSP 1.6.1

examples/make.mk

@@ -46,6 +46,7 @@ SRC_C += $(subst $(TOP)/,,$(wildcard $(TOP)/hw/bsp/$(BOARD)/*.c))
 
 # Compiler Flags
 CFLAGS += \
+  -ggdb \
   -fdata-sections \
   -ffunction-sections \
   -fsingle-precision-constant \
@@ -68,7 +69,7 @@ CFLAGS += \
 
 # Debugging/Optimization
 ifeq ($(DEBUG), 1)
-  CFLAGS += -Og -ggdb
+  CFLAGS += -Og
 else
   CFLAGS += -Os
 endif
@@ -81,13 +82,10 @@ endif
 # Logger: default is uart, can be set to rtt or swo
 ifeq ($(LOGGER),rtt)
   RTT_SRC = lib/SEGGER_RTT
-	
   CFLAGS += -DLOGGER_RTT -DSEGGER_RTT_MODE_DEFAULT=SEGGER_RTT_MODE_BLOCK_IF_FIFO_FULL
   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
-
 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.