readme updated

misc0110 · misc0110 · commit 5368024ab912 · 2015-12-01T19:03:25.000+01:00
diff --git a/README.md b/README.md
@@ -1,4 +1,38 @@
 Universal Header Decoder
 =================
 
+This tool takes one or more description of a binary header and decodes the header of a given file.
 
+# Usage
+
+`python3 ./hdec.py <file-to-decode> <type> <header description> [<header 2 description> ...]`
+
+# Header
+
+Header files consist of a line-by-line description of each header field. Each line has the form
+```
+Name: Size in bits
+```
+or 
+```
+Name: Size in bits: display type
+```
+
++ **Name** is displayed as field name
++ **Size in bits** determines the field size in bits. 
+    It can also be a mathematical expression and can use previously parsed fields (referenced by their name)
++ **display type** (optional) defines how the value should be displayed. 
+    It is a comma separated list with the following possible types: *int*, *hex*, *str*, *bin*, *intE* (int with changed endianness). 
+    The default is *int, hex, bin* if this field is not given.
+
+# Example
+
+## IPv6 Packets
+
+`python3 ./hdec.py sample/ipv6_icmpv6 hex header/IPv6 header/ICMPv6`
+`python3 ./hdec.py sample/ipv6_udp hex header/IPv6 header/UDP`
+`python3 ./hdec.py sample/6lowpan_iphc hex header/IPHC`
+
+## Bitmap
+
+`python3 ./hdec.py sample/bitmap.bmp raw header/BMP`
