diff --git a/bootloader/build_multi_image.sh b/bootloader/build_multi_image.sh
index db1943a918de7e67d9d30a4c5bf89d4bcdf16f3e..94a3b46b12b2ead338da2d14794ff19cc4c08278 100755
--- a/bootloader/build_multi_image.sh
+++ b/bootloader/build_multi_image.sh
@@ -1,14 +1,13 @@
 #!/bin/sh
 set -e
 
-echo "build multi image" $1 $2 $3 $4
 PYTHON="$1"
 BIN1="$2"
 BIN2="$3"
 BINOUT="$4"
 
-dd if=/dev/zero ibs=1k count=448 | tr "\000" "\377" > "$BINOUT"
-dd if="$BIN1" of="$BINOUT" conv=notrunc
-dd if="$BIN2" of="$BINOUT" conv=notrunc oflag=append
+dd if=/dev/zero ibs=1k count=448 2>/dev/null | tr "\000" "\377" > "$BINOUT"
+dd if="$BIN1" of="$BINOUT" conv=notrunc 2>/dev/null
+dd if="$BIN2" of="$BINOUT" conv=notrunc oflag=append 2>/dev/null
 
 "$PYTHON" "$(dirname "$0")/crc_patch.py" "$BINOUT"
diff --git a/bootloader/crc_patch.py b/bootloader/crc_patch.py
index 21eeb57a5d1894bbdb4bcfc3bb0dbb889478de61..59ec6befb14a5dc625139e8042363ce2ac86f3ed 100755
--- a/bootloader/crc_patch.py
+++ b/bootloader/crc_patch.py
@@ -2,16 +2,19 @@
 import sys
 import crc16
 
-crc = 0
 
-data = open(sys.argv[1], 'rb').read()
-crc = crc16.crc16xmodem(data)
-print(crc)
+def main():
+    data = open(sys.argv[1], 'rb').read()
+    crc = crc16.crc16xmodem(data)
+    # print(crc)
 
-padded = data + bytes([crc >> 8, crc & 0xFF])
+    padded = data + bytes([crc >> 8, crc & 0xFF])
 
-crc = 0
-crc = crc16.crc16xmodem(padded)
-print(crc)
+    crc = crc16.crc16xmodem(padded)
+    # print(crc)
 
-open(sys.argv[1], 'wb').write(padded)
+    open(sys.argv[1], 'wb').write(padded)
+
+
+if __name__ == "__main__":
+    main()