Friday, March 20, 2009

Coverage convergence technology (CCT)

CCT automates the process of going between coverage goals and determining what constraints to modify, then modifying the constraint to achive the functional coverage goal. CCT also has a provision to automatically generate functional coverage groups from the VERA/NTB/System verilog code based on the constraints specified.

The automatically generated functional coverage code can be used as the starting point for writing the functional coverage model and can be integrated with the DV enviroment. CCT also allows parallel test runs with each test run targetting different coverage points without having any overlap between them. parallel test runs without overlapping random values is achived by providing the tool with a bias file which is generated by the tool based on the functional coverage data base.

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