Question

I would like to know what the keyword try is used for in Specman and especially its usage in the code snippet given below:

try {
    unpack(packing.low,lob,pkt);
} else{
    message(LOW, “Uh-oh!”){print lob using HEX;};
    message(LOW,”bad unpack!!!”);
};

Answer 1

try and else are Specman’s exception handling constructs. If an error is created in the try block, then the else block is immediately executed instead of the rest of the try block and the error is suppressed with no printout.

In this case, if lob has more bits than pkt has “physical fields”, then the unpack will generate an error. If that happens, the Specman runtime will jump to the else block and print out the lob data structure instead of printing the original unpack error. Look in the docs with regards to what “physical fields” are and how they are used. They are a strange construct that specifically interacts with the behavior of Specman’s %, pack, and unpack constructs. Physical fields of pkt will be declared with the % modifier preceding the “physical fields” of pkt.