Add SKR Mini E3 V3.0.1 _xfer Environment

Similar to SKR Mini E3 V3's _xfer environment.

ini/stm32f4.ini

@@ -745,6 +745,20 @@ build_flags                 = ${stm32_variant.build_flags}
 upload_protocol             = stlink
 debug_tool                  = stlink
 
+#
+# BigTreeTech SKR Mini E3 V3.0.1 (STM32F401RCT6 ARM Cortex-M0+)
+# Custom upload to SD via Marlin with Binary Protocol
+# Requires Marlin with BINARY_FILE_TRANSFER already installed on the target board.
+# If CUSTOM_FIRMWARE_UPLOAD is also installed, Marlin will reboot the board to install the firmware.
+# Currently CUSTOM_FIRMWARE_UPLOAD must also be enabled to use 'xfer' build envs.
+#
+[env:STM32F401RC_btt_xfer]
+extends         = env:STM32F401RC_btt
+build_flags     = ${env:STM32F401RC_btt.build_flags} -DXFER_BUILD
+extra_scripts   = ${env:STM32F401RC_btt.extra_scripts}
+                  pre:buildroot/share/scripts/upload.py
+upload_protocol = custom
+
 #
 # MKS SKIPR v1.0 all-in-one board (STM32F407VE)
 #