Add flash target for UF2 bootloaders (#16525)

docs/flashing.md

@@ -347,3 +347,14 @@ Flashing sequence:
 2. Wait for the OS to detect the device
 3. Copy the .uf2 file to the new USB disk
 4. Wait for the keyboard to become available
+
+or
+
+CLI Flashing sequence:
+
+1. Enter the bootloader using any of the following methods:
+    * Tap the `RESET` keycode
+    * Double-tap the `nRST` button on the PCB.
+2. Wait for the OS to detect the device
+3. Flash via QMK CLI eg. `qmk flash --keyboard handwired/onekey/blackpill_f411_tinyuf2 --keymap default`
+4. Wait for the keyboard to become available

platforms/chibios/flash.mk

@@ -40,6 +40,18 @@ endef
 dfu-util: $(BUILD_DIR)/$(TARGET).bin cpfirmware sizeafter
 	$(call EXEC_DFU_UTIL)
 
+define EXEC_UF2_UTIL_DEPLOY
+	if ! $(UF2CONV) --deploy $(BUILD_DIR)/$(TARGET).uf2 2>/dev/null; then \
+		printf "$(MSG_BOOTLOADER_NOT_FOUND_QUICK_RETRY)" ;\
+		sleep $(BOOTLOADER_RETRY_TIME) ;\
+		while ! $(UF2CONV) --deploy $(BUILD_DIR)/$(TARGET).uf2  2>/dev/null; do \
+			printf "." ;\
+			sleep $(BOOTLOADER_RETRY_TIME) ;\
+		done ;\
+		printf "\n" ;\
+	fi
+endef
+
 # TODO: Remove once ARM has a way to configure EECONFIG_HANDEDNESS
 #       within the emulated eeprom via dfu-util or another tool
 ifneq (,$(filter $(MAKECMDGOALS),dfu-util-split-left))
@@ -90,6 +102,8 @@ ifneq ($(strip $(PROGRAM_CMD)),)
 	$(UNSYNC_OUTPUT_CMD) && $(PROGRAM_CMD)
 else ifeq ($(strip $(BOOTLOADER)),kiibohd)
 	$(UNSYNC_OUTPUT_CMD) && $(call EXEC_DFU_UTIL)
+else ifeq ($(strip $(BOOTLOADER)),tinyuf2)
+	$(UNSYNC_OUTPUT_CMD) && $(call EXEC_UF2_UTIL_DEPLOY)
 else ifeq ($(strip $(MCU_FAMILY)),KINETIS)
 	$(UNSYNC_OUTPUT_CMD) && $(call EXEC_TEENSY)
 else ifeq ($(strip $(MCU_FAMILY)),MIMXRT1062)

util/uf2conv.py

@@ -267,7 +267,7 @@ def load_families():
 def main():
     global appstartaddr, familyid
     def error(msg):
-        print(msg)
+        print(msg, file=sys.stderr)
         sys.exit(1)
     parser = argparse.ArgumentParser(description='Convert to UF2 or flash directly.')
     parser.add_argument('input', metavar='INPUT', type=str, nargs='?',