basic block XML

<?xml version="1.0"?>
<block>
    <name>Stream CRC</name>
    <key>stream_crc</key>
    <category>PCTC</category>
    <import>import stream_crc</import>
    <make>stream_crc.stream_crc($packet_len, $len_tag_key)</make>
    <param>
        <name>Packet Length</name>
        <key>packet_len</key>
        <type>int</type>
    </param>
    <param>
        <name>Length Tag Key</name>
        <key>len_tag_key</key>
        <value>"packet_len"</value>
        <type>string</type>
    </param>
    <sink>
        <name>in</name>
        <type>byte</type>
    </sink>
    <source>
        <name>out</name>
        <type>byte</type>
    </source>
</block>