Sunday, March 1, 2009

Streaming operators --- System verilog

In VERA/NTB we have vera_pack & vera_unpack methods to pack a class object to bit stream or unpack a bit stream to a class object. System verilog does not have a pack or unpack methods the replacement for this methods are the Streaming operators << , >>. These operaters have the same functionality as the pack/unpack methods. We frequently see the usage of pack and unpack methods while extending the RVM/VMM classes like rvm_data/vmm_data.

Following is an example on the usage of Streaming operators

byte stream[$]; // byte stream

class Packet
rand int header;
rand int len;
rand byte payload[];
int crc;
constraint G { len > 1; payload.size == len ; }
function void post_randomize; crc = payload.sum; endfunction

send: begin // Create random packer and transmit
byte q[$];
Packet p = new;
q = {<< byte{p.header, p.len, p.payload, p.crc}}; // pack
stream = {stream, q}; // append to stream

receive: begin // Receive packet, unpack, and remove
byte q[$];
Packet p = new;
{<< byte{ p.header, p.len, p.payload with [0 +: p.len], p.crc }} = stream;
stream = stream[ $bits(p) / 8 : $ ]; // remove packet

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